GNU Linux-libre 6.1.90-gnu

[releases.git] / fs / btrfs / scrub.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2011, 2012 STRATO.  All rights reserved.
 */

#include <linux/blkdev.h>
#include <linux/ratelimit.h>
#include <linux/sched/mm.h>
#include <crypto/hash.h>
#include "ctree.h"
#include "discard.h"
#include "volumes.h"
#include "disk-io.h"
#include "ordered-data.h"
#include "transaction.h"
#include "backref.h"
#include "extent_io.h"
#include "dev-replace.h"
#include "check-integrity.h"
#include "rcu-string.h"
#include "raid56.h"
#include "block-group.h"
#include "zoned.h"

/*
 * This is only the first step towards a full-features scrub. It reads all
 * extent and super block and verifies the checksums. In case a bad checksum
 * is found or the extent cannot be read, good data will be written back if
 * any can be found.
 *
 * Future enhancements:
 *  - In case an unrepairable extent is encountered, track which files are
 *    affected and report them
 *  - track and record media errors, throw out bad devices
 *  - add a mode to also read unallocated space
 */

struct scrub_block;
struct scrub_ctx;

/*
 * The following three values only influence the performance.
 *
 * The last one configures the number of parallel and outstanding I/O
 * operations. The first one configures an upper limit for the number
 * of (dynamically allocated) pages that are added to a bio.
 */
#define SCRUB_SECTORS_PER_BIO   32      /* 128KiB per bio for 4KiB pages */
#define SCRUB_BIOS_PER_SCTX     64      /* 8MiB per device in flight for 4KiB pages */

/*
 * The following value times PAGE_SIZE needs to be large enough to match the
 * largest node/leaf/sector size that shall be supported.
 */
#define SCRUB_MAX_SECTORS_PER_BLOCK     (BTRFS_MAX_METADATA_BLOCKSIZE / SZ_4K)

#define SCRUB_MAX_PAGES                 (DIV_ROUND_UP(BTRFS_MAX_METADATA_BLOCKSIZE, PAGE_SIZE))

struct scrub_recover {
        refcount_t              refs;
        struct btrfs_io_context *bioc;
        u64                     map_length;
};

struct scrub_sector {
        struct scrub_block      *sblock;
        struct list_head        list;
        u64                     flags;  /* extent flags */
        u64                     generation;
        /* Offset in bytes to @sblock. */
        u32                     offset;
        atomic_t                refs;
        unsigned int            have_csum:1;
        unsigned int            io_error:1;
        u8                      csum[BTRFS_CSUM_SIZE];

        struct scrub_recover    *recover;
};

struct scrub_bio {
        int                     index;
        struct scrub_ctx        *sctx;
        struct btrfs_device     *dev;
        struct bio              *bio;
        blk_status_t            status;
        u64                     logical;
        u64                     physical;
        struct scrub_sector     *sectors[SCRUB_SECTORS_PER_BIO];
        int                     sector_count;
        int                     next_free;
        struct work_struct      work;
};

struct scrub_block {
        /*
         * Each page will have its page::private used to record the logical
         * bytenr.
         */
        struct page             *pages[SCRUB_MAX_PAGES];
        struct scrub_sector     *sectors[SCRUB_MAX_SECTORS_PER_BLOCK];
        struct btrfs_device     *dev;
        /* Logical bytenr of the sblock */
        u64                     logical;
        u64                     physical;
        u64                     physical_for_dev_replace;
        /* Length of sblock in bytes */
        u32                     len;
        int                     sector_count;
        int                     mirror_num;

        atomic_t                outstanding_sectors;
        refcount_t              refs; /* free mem on transition to zero */
        struct scrub_ctx        *sctx;
        struct scrub_parity     *sparity;
        struct {
                unsigned int    header_error:1;
                unsigned int    checksum_error:1;
                unsigned int    no_io_error_seen:1;
                unsigned int    generation_error:1; /* also sets header_error */

                /* The following is for the data used to check parity */
                /* It is for the data with checksum */
                unsigned int    data_corrected:1;
        };
        struct work_struct      work;
};

/* Used for the chunks with parity stripe such RAID5/6 */
struct scrub_parity {
        struct scrub_ctx        *sctx;

        struct btrfs_device     *scrub_dev;

        u64                     logic_start;

        u64                     logic_end;

        int                     nsectors;

        u32                     stripe_len;

        refcount_t              refs;

        struct list_head        sectors_list;

        /* Work of parity check and repair */
        struct work_struct      work;

        /* Mark the parity blocks which have data */
        unsigned long           dbitmap;

        /*
         * Mark the parity blocks which have data, but errors happen when
         * read data or check data
         */
        unsigned long           ebitmap;
};

struct scrub_ctx {
        struct scrub_bio        *bios[SCRUB_BIOS_PER_SCTX];
        struct btrfs_fs_info    *fs_info;
        int                     first_free;
        int                     curr;
        atomic_t                bios_in_flight;
        atomic_t                workers_pending;
        spinlock_t              list_lock;
        wait_queue_head_t       list_wait;
        struct list_head        csum_list;
        atomic_t                cancel_req;
        int                     readonly;
        int                     sectors_per_bio;

        /* State of IO submission throttling affecting the associated device */
        ktime_t                 throttle_deadline;
        u64                     throttle_sent;

        int                     is_dev_replace;
        u64                     write_pointer;

        struct scrub_bio        *wr_curr_bio;
        struct mutex            wr_lock;
        struct btrfs_device     *wr_tgtdev;
        bool                    flush_all_writes;

        /*
         * statistics
         */
        struct btrfs_scrub_progress stat;
        spinlock_t              stat_lock;

        /*
         * Use a ref counter to avoid use-after-free issues. Scrub workers
         * decrement bios_in_flight and workers_pending and then do a wakeup
         * on the list_wait wait queue. We must ensure the main scrub task
         * doesn't free the scrub context before or while the workers are
         * doing the wakeup() call.
         */
        refcount_t              refs;
};

struct scrub_warning {
        struct btrfs_path       *path;
        u64                     extent_item_size;
        const char              *errstr;
        u64                     physical;
        u64                     logical;
        struct btrfs_device     *dev;
};

struct full_stripe_lock {
        struct rb_node node;
        u64 logical;
        u64 refs;
        struct mutex mutex;
};

#ifndef CONFIG_64BIT
/* This structure is for archtectures whose (void *) is smaller than u64 */
struct scrub_page_private {
        u64 logical;
};
#endif

static int attach_scrub_page_private(struct page *page, u64 logical)
{
#ifdef CONFIG_64BIT
        attach_page_private(page, (void *)logical);
        return 0;
#else
        struct scrub_page_private *spp;

        spp = kmalloc(sizeof(*spp), GFP_KERNEL);
        if (!spp)
                return -ENOMEM;
        spp->logical = logical;
        attach_page_private(page, (void *)spp);
        return 0;
#endif
}

static void detach_scrub_page_private(struct page *page)
{
#ifdef CONFIG_64BIT
        detach_page_private(page);
        return;
#else
        struct scrub_page_private *spp;

        spp = detach_page_private(page);
        kfree(spp);
        return;
#endif
}

static struct scrub_block *alloc_scrub_block(struct scrub_ctx *sctx,
                                             struct btrfs_device *dev,
                                             u64 logical, u64 physical,
                                             u64 physical_for_dev_replace,
                                             int mirror_num)
{
        struct scrub_block *sblock;

        sblock = kzalloc(sizeof(*sblock), GFP_KERNEL);
        if (!sblock)
                return NULL;
        refcount_set(&sblock->refs, 1);
        sblock->sctx = sctx;
        sblock->logical = logical;
        sblock->physical = physical;
        sblock->physical_for_dev_replace = physical_for_dev_replace;
        sblock->dev = dev;
        sblock->mirror_num = mirror_num;
        sblock->no_io_error_seen = 1;
        /*
         * Scrub_block::pages will be allocated at alloc_scrub_sector() when
         * the corresponding page is not allocated.
         */
        return sblock;
}

/*
 * Allocate a new scrub sector and attach it to @sblock.
 *
 * Will also allocate new pages for @sblock if needed.
 */
static struct scrub_sector *alloc_scrub_sector(struct scrub_block *sblock,
                                               u64 logical, gfp_t gfp)
{
        const pgoff_t page_index = (logical - sblock->logical) >> PAGE_SHIFT;
        struct scrub_sector *ssector;

        /* We must never have scrub_block exceed U32_MAX in size. */
        ASSERT(logical - sblock->logical < U32_MAX);

        ssector = kzalloc(sizeof(*ssector), gfp);
        if (!ssector)
                return NULL;

        /* Allocate a new page if the slot is not allocated */
        if (!sblock->pages[page_index]) {
                int ret;

                sblock->pages[page_index] = alloc_page(gfp);
                if (!sblock->pages[page_index]) {
                        kfree(ssector);
                        return NULL;
                }
                ret = attach_scrub_page_private(sblock->pages[page_index],
                                sblock->logical + (page_index << PAGE_SHIFT));
                if (ret < 0) {
                        kfree(ssector);
                        __free_page(sblock->pages[page_index]);
                        sblock->pages[page_index] = NULL;
                        return NULL;
                }
        }

        atomic_set(&ssector->refs, 1);
        ssector->sblock = sblock;
        /* The sector to be added should not be used */
        ASSERT(sblock->sectors[sblock->sector_count] == NULL);
        ssector->offset = logical - sblock->logical;

        /* The sector count must be smaller than the limit */
        ASSERT(sblock->sector_count < SCRUB_MAX_SECTORS_PER_BLOCK);

        sblock->sectors[sblock->sector_count] = ssector;
        sblock->sector_count++;
        sblock->len += sblock->sctx->fs_info->sectorsize;

        return ssector;
}

static struct page *scrub_sector_get_page(struct scrub_sector *ssector)
{
        struct scrub_block *sblock = ssector->sblock;
        pgoff_t index;
        /*
         * When calling this function, ssector must be alreaday attached to the
         * parent sblock.
         */
        ASSERT(sblock);

        /* The range should be inside the sblock range */
        ASSERT(ssector->offset < sblock->len);

        index = ssector->offset >> PAGE_SHIFT;
        ASSERT(index < SCRUB_MAX_PAGES);
        ASSERT(sblock->pages[index]);
        ASSERT(PagePrivate(sblock->pages[index]));
        return sblock->pages[index];
}

static unsigned int scrub_sector_get_page_offset(struct scrub_sector *ssector)
{
        struct scrub_block *sblock = ssector->sblock;

        /*
         * When calling this function, ssector must be already attached to the
         * parent sblock.
         */
        ASSERT(sblock);

        /* The range should be inside the sblock range */
        ASSERT(ssector->offset < sblock->len);

        return offset_in_page(ssector->offset);
}

static char *scrub_sector_get_kaddr(struct scrub_sector *ssector)
{
        return page_address(scrub_sector_get_page(ssector)) +
               scrub_sector_get_page_offset(ssector);
}

static int bio_add_scrub_sector(struct bio *bio, struct scrub_sector *ssector,
                                unsigned int len)
{
        return bio_add_page(bio, scrub_sector_get_page(ssector), len,
                            scrub_sector_get_page_offset(ssector));
}

static int scrub_setup_recheck_block(struct scrub_block *original_sblock,
                                     struct scrub_block *sblocks_for_recheck[]);
static void scrub_recheck_block(struct btrfs_fs_info *fs_info,
                                struct scrub_block *sblock,
                                int retry_failed_mirror);
static void scrub_recheck_block_checksum(struct scrub_block *sblock);
static int scrub_repair_block_from_good_copy(struct scrub_block *sblock_bad,
                                             struct scrub_block *sblock_good);
static int scrub_repair_sector_from_good_copy(struct scrub_block *sblock_bad,
                                            struct scrub_block *sblock_good,
                                            int sector_num, int force_write);
static void scrub_write_block_to_dev_replace(struct scrub_block *sblock);
static int scrub_write_sector_to_dev_replace(struct scrub_block *sblock,
                                             int sector_num);
static int scrub_checksum_data(struct scrub_block *sblock);
static int scrub_checksum_tree_block(struct scrub_block *sblock);
static int scrub_checksum_super(struct scrub_block *sblock);
static void scrub_block_put(struct scrub_block *sblock);
static void scrub_sector_get(struct scrub_sector *sector);
static void scrub_sector_put(struct scrub_sector *sector);
static void scrub_parity_get(struct scrub_parity *sparity);
static void scrub_parity_put(struct scrub_parity *sparity);
static int scrub_sectors(struct scrub_ctx *sctx, u64 logical, u32 len,
                         u64 physical, struct btrfs_device *dev, u64 flags,
                         u64 gen, int mirror_num, u8 *csum,
                         u64 physical_for_dev_replace);
static void scrub_bio_end_io(struct bio *bio);
static void scrub_bio_end_io_worker(struct work_struct *work);
static void scrub_block_complete(struct scrub_block *sblock);
static void scrub_find_good_copy(struct btrfs_fs_info *fs_info,
                                 u64 extent_logical, u32 extent_len,
                                 u64 *extent_physical,
                                 struct btrfs_device **extent_dev,
                                 int *extent_mirror_num);
static int scrub_add_sector_to_wr_bio(struct scrub_ctx *sctx,
                                      struct scrub_sector *sector);
static void scrub_wr_submit(struct scrub_ctx *sctx);
static void scrub_wr_bio_end_io(struct bio *bio);
static void scrub_wr_bio_end_io_worker(struct work_struct *work);
static void scrub_put_ctx(struct scrub_ctx *sctx);

static inline int scrub_is_page_on_raid56(struct scrub_sector *sector)
{
        return sector->recover &&
               (sector->recover->bioc->map_type & BTRFS_BLOCK_GROUP_RAID56_MASK);
}

static void scrub_pending_bio_inc(struct scrub_ctx *sctx)
{
        refcount_inc(&sctx->refs);
        atomic_inc(&sctx->bios_in_flight);
}

static void scrub_pending_bio_dec(struct scrub_ctx *sctx)
{
        atomic_dec(&sctx->bios_in_flight);
        wake_up(&sctx->list_wait);
        scrub_put_ctx(sctx);
}

static void __scrub_blocked_if_needed(struct btrfs_fs_info *fs_info)
{
        while (atomic_read(&fs_info->scrub_pause_req)) {
                mutex_unlock(&fs_info->scrub_lock);
                wait_event(fs_info->scrub_pause_wait,
                   atomic_read(&fs_info->scrub_pause_req) == 0);
                mutex_lock(&fs_info->scrub_lock);
        }
}

static void scrub_pause_on(struct btrfs_fs_info *fs_info)
{
        atomic_inc(&fs_info->scrubs_paused);
        wake_up(&fs_info->scrub_pause_wait);
}

static void scrub_pause_off(struct btrfs_fs_info *fs_info)
{
        mutex_lock(&fs_info->scrub_lock);
        __scrub_blocked_if_needed(fs_info);
        atomic_dec(&fs_info->scrubs_paused);
        mutex_unlock(&fs_info->scrub_lock);

        wake_up(&fs_info->scrub_pause_wait);
}

static void scrub_blocked_if_needed(struct btrfs_fs_info *fs_info)
{
        scrub_pause_on(fs_info);
        scrub_pause_off(fs_info);
}

/*
 * Insert new full stripe lock into full stripe locks tree
 *
 * Return pointer to existing or newly inserted full_stripe_lock structure if
 * everything works well.
 * Return ERR_PTR(-ENOMEM) if we failed to allocate memory
 *
 * NOTE: caller must hold full_stripe_locks_root->lock before calling this
 * function
 */
static struct full_stripe_lock *insert_full_stripe_lock(
                struct btrfs_full_stripe_locks_tree *locks_root,
                u64 fstripe_logical)
{
        struct rb_node **p;
        struct rb_node *parent = NULL;
        struct full_stripe_lock *entry;
        struct full_stripe_lock *ret;

        lockdep_assert_held(&locks_root->lock);

        p = &locks_root->root.rb_node;
        while (*p) {
                parent = *p;
                entry = rb_entry(parent, struct full_stripe_lock, node);
                if (fstripe_logical < entry->logical) {
                        p = &(*p)->rb_left;
                } else if (fstripe_logical > entry->logical) {
                        p = &(*p)->rb_right;
                } else {
                        entry->refs++;
                        return entry;
                }
        }

        /*
         * Insert new lock.
         */
        ret = kmalloc(sizeof(*ret), GFP_KERNEL);
        if (!ret)
                return ERR_PTR(-ENOMEM);
        ret->logical = fstripe_logical;
        ret->refs = 1;
        mutex_init(&ret->mutex);

        rb_link_node(&ret->node, parent, p);
        rb_insert_color(&ret->node, &locks_root->root);
        return ret;
}

/*
 * Search for a full stripe lock of a block group
 *
 * Return pointer to existing full stripe lock if found
 * Return NULL if not found
 */
static struct full_stripe_lock *search_full_stripe_lock(
                struct btrfs_full_stripe_locks_tree *locks_root,
                u64 fstripe_logical)
{
        struct rb_node *node;
        struct full_stripe_lock *entry;

        lockdep_assert_held(&locks_root->lock);

        node = locks_root->root.rb_node;
        while (node) {
                entry = rb_entry(node, struct full_stripe_lock, node);
                if (fstripe_logical < entry->logical)
                        node = node->rb_left;
                else if (fstripe_logical > entry->logical)
                        node = node->rb_right;
                else
                        return entry;
        }
        return NULL;
}

/*
 * Helper to get full stripe logical from a normal bytenr.
 *
 * Caller must ensure @cache is a RAID56 block group.
 */
static u64 get_full_stripe_logical(struct btrfs_block_group *cache, u64 bytenr)
{
        u64 ret;

        /*
         * Due to chunk item size limit, full stripe length should not be
         * larger than U32_MAX. Just a sanity check here.
         */
        WARN_ON_ONCE(cache->full_stripe_len >= U32_MAX);

        /*
         * round_down() can only handle power of 2, while RAID56 full
         * stripe length can be 64KiB * n, so we need to manually round down.
         */
        ret = div64_u64(bytenr - cache->start, cache->full_stripe_len) *
                        cache->full_stripe_len + cache->start;
        return ret;
}

/*
 * Lock a full stripe to avoid concurrency of recovery and read
 *
 * It's only used for profiles with parities (RAID5/6), for other profiles it
 * does nothing.
 *
 * Return 0 if we locked full stripe covering @bytenr, with a mutex held.
 * So caller must call unlock_full_stripe() at the same context.
 *
 * Return <0 if encounters error.
 */
static int lock_full_stripe(struct btrfs_fs_info *fs_info, u64 bytenr,
                            bool *locked_ret)
{
        struct btrfs_block_group *bg_cache;
        struct btrfs_full_stripe_locks_tree *locks_root;
        struct full_stripe_lock *existing;
        u64 fstripe_start;
        int ret = 0;

        *locked_ret = false;
        bg_cache = btrfs_lookup_block_group(fs_info, bytenr);
        if (!bg_cache) {
                ASSERT(0);
                return -ENOENT;
        }

        /* Profiles not based on parity don't need full stripe lock */
        if (!(bg_cache->flags & BTRFS_BLOCK_GROUP_RAID56_MASK))
                goto out;
        locks_root = &bg_cache->full_stripe_locks_root;

        fstripe_start = get_full_stripe_logical(bg_cache, bytenr);

        /* Now insert the full stripe lock */
        mutex_lock(&locks_root->lock);
        existing = insert_full_stripe_lock(locks_root, fstripe_start);
        mutex_unlock(&locks_root->lock);
        if (IS_ERR(existing)) {
                ret = PTR_ERR(existing);
                goto out;
        }
        mutex_lock(&existing->mutex);
        *locked_ret = true;
out:
        btrfs_put_block_group(bg_cache);
        return ret;
}

/*
 * Unlock a full stripe.
 *
 * NOTE: Caller must ensure it's the same context calling corresponding
 * lock_full_stripe().
 *
 * Return 0 if we unlock full stripe without problem.
 * Return <0 for error
 */
static int unlock_full_stripe(struct btrfs_fs_info *fs_info, u64 bytenr,
                              bool locked)
{
        struct btrfs_block_group *bg_cache;
        struct btrfs_full_stripe_locks_tree *locks_root;
        struct full_stripe_lock *fstripe_lock;
        u64 fstripe_start;
        bool freeit = false;
        int ret = 0;

        /* If we didn't acquire full stripe lock, no need to continue */
        if (!locked)
                return 0;

        bg_cache = btrfs_lookup_block_group(fs_info, bytenr);
        if (!bg_cache) {
                ASSERT(0);
                return -ENOENT;
        }
        if (!(bg_cache->flags & BTRFS_BLOCK_GROUP_RAID56_MASK))
                goto out;

        locks_root = &bg_cache->full_stripe_locks_root;
        fstripe_start = get_full_stripe_logical(bg_cache, bytenr);

        mutex_lock(&locks_root->lock);
        fstripe_lock = search_full_stripe_lock(locks_root, fstripe_start);
        /* Unpaired unlock_full_stripe() detected */
        if (!fstripe_lock) {
                WARN_ON(1);
                ret = -ENOENT;
                mutex_unlock(&locks_root->lock);
                goto out;
        }

        if (fstripe_lock->refs == 0) {
                WARN_ON(1);
                btrfs_warn(fs_info, "full stripe lock at %llu refcount underflow",
                        fstripe_lock->logical);
        } else {
                fstripe_lock->refs--;
        }

        if (fstripe_lock->refs == 0) {
                rb_erase(&fstripe_lock->node, &locks_root->root);
                freeit = true;
        }
        mutex_unlock(&locks_root->lock);

        mutex_unlock(&fstripe_lock->mutex);
        if (freeit)
                kfree(fstripe_lock);
out:
        btrfs_put_block_group(bg_cache);
        return ret;
}

static void scrub_free_csums(struct scrub_ctx *sctx)
{
        while (!list_empty(&sctx->csum_list)) {
                struct btrfs_ordered_sum *sum;
                sum = list_first_entry(&sctx->csum_list,
                                       struct btrfs_ordered_sum, list);
                list_del(&sum->list);
                kfree(sum);
        }
}

static noinline_for_stack void scrub_free_ctx(struct scrub_ctx *sctx)
{
        int i;

        if (!sctx)
                return;

        /* this can happen when scrub is cancelled */
        if (sctx->curr != -1) {
                struct scrub_bio *sbio = sctx->bios[sctx->curr];

                for (i = 0; i < sbio->sector_count; i++)
                        scrub_block_put(sbio->sectors[i]->sblock);
                bio_put(sbio->bio);
        }

        for (i = 0; i < SCRUB_BIOS_PER_SCTX; ++i) {
                struct scrub_bio *sbio = sctx->bios[i];

                if (!sbio)
                        break;
                kfree(sbio);
        }

        kfree(sctx->wr_curr_bio);
        scrub_free_csums(sctx);
        kfree(sctx);
}

static void scrub_put_ctx(struct scrub_ctx *sctx)
{
        if (refcount_dec_and_test(&sctx->refs))
                scrub_free_ctx(sctx);
}

static noinline_for_stack struct scrub_ctx *scrub_setup_ctx(
                struct btrfs_fs_info *fs_info, int is_dev_replace)
{
        struct scrub_ctx *sctx;
        int             i;

        sctx = kzalloc(sizeof(*sctx), GFP_KERNEL);
        if (!sctx)
                goto nomem;
        refcount_set(&sctx->refs, 1);
        sctx->is_dev_replace = is_dev_replace;
        sctx->sectors_per_bio = SCRUB_SECTORS_PER_BIO;
        sctx->curr = -1;
        sctx->fs_info = fs_info;
        INIT_LIST_HEAD(&sctx->csum_list);
        for (i = 0; i < SCRUB_BIOS_PER_SCTX; ++i) {
                struct scrub_bio *sbio;

                sbio = kzalloc(sizeof(*sbio), GFP_KERNEL);
                if (!sbio)
                        goto nomem;
                sctx->bios[i] = sbio;

                sbio->index = i;
                sbio->sctx = sctx;
                sbio->sector_count = 0;
                INIT_WORK(&sbio->work, scrub_bio_end_io_worker);

                if (i != SCRUB_BIOS_PER_SCTX - 1)
                        sctx->bios[i]->next_free = i + 1;
                else
                        sctx->bios[i]->next_free = -1;
        }
        sctx->first_free = 0;
        atomic_set(&sctx->bios_in_flight, 0);
        atomic_set(&sctx->workers_pending, 0);
        atomic_set(&sctx->cancel_req, 0);

        spin_lock_init(&sctx->list_lock);
        spin_lock_init(&sctx->stat_lock);
        init_waitqueue_head(&sctx->list_wait);
        sctx->throttle_deadline = 0;

        WARN_ON(sctx->wr_curr_bio != NULL);
        mutex_init(&sctx->wr_lock);
        sctx->wr_curr_bio = NULL;
        if (is_dev_replace) {
                WARN_ON(!fs_info->dev_replace.tgtdev);
                sctx->wr_tgtdev = fs_info->dev_replace.tgtdev;
                sctx->flush_all_writes = false;
        }

        return sctx;

nomem:
        scrub_free_ctx(sctx);
        return ERR_PTR(-ENOMEM);
}

static int scrub_print_warning_inode(u64 inum, u64 offset, u64 root,
                                     void *warn_ctx)
{
        u32 nlink;
        int ret;
        int i;
        unsigned nofs_flag;
        struct extent_buffer *eb;
        struct btrfs_inode_item *inode_item;
        struct scrub_warning *swarn = warn_ctx;
        struct btrfs_fs_info *fs_info = swarn->dev->fs_info;
        struct inode_fs_paths *ipath = NULL;
        struct btrfs_root *local_root;
        struct btrfs_key key;

        local_root = btrfs_get_fs_root(fs_info, root, true);
        if (IS_ERR(local_root)) {
                ret = PTR_ERR(local_root);
                goto err;
        }

        /*
         * this makes the path point to (inum INODE_ITEM ioff)
         */
        key.objectid = inum;
        key.type = BTRFS_INODE_ITEM_KEY;
        key.offset = 0;

        ret = btrfs_search_slot(NULL, local_root, &key, swarn->path, 0, 0);
        if (ret) {
                btrfs_put_root(local_root);
                btrfs_release_path(swarn->path);
                goto err;
        }

        eb = swarn->path->nodes[0];
        inode_item = btrfs_item_ptr(eb, swarn->path->slots[0],
                                        struct btrfs_inode_item);
        nlink = btrfs_inode_nlink(eb, inode_item);
        btrfs_release_path(swarn->path);

        /*
         * init_path might indirectly call vmalloc, or use GFP_KERNEL. Scrub
         * uses GFP_NOFS in this context, so we keep it consistent but it does
         * not seem to be strictly necessary.
         */
        nofs_flag = memalloc_nofs_save();
        ipath = init_ipath(4096, local_root, swarn->path);
        memalloc_nofs_restore(nofs_flag);
        if (IS_ERR(ipath)) {
                btrfs_put_root(local_root);
                ret = PTR_ERR(ipath);
                ipath = NULL;
                goto err;
        }
        ret = paths_from_inode(inum, ipath);

        if (ret < 0)
                goto err;

        /*
         * we deliberately ignore the bit ipath might have been too small to
         * hold all of the paths here
         */
        for (i = 0; i < ipath->fspath->elem_cnt; ++i)
                btrfs_warn_in_rcu(fs_info,
"%s at logical %llu on dev %s, physical %llu, root %llu, inode %llu, offset %llu, length %u, links %u (path: %s)",
                                  swarn->errstr, swarn->logical,
                                  rcu_str_deref(swarn->dev->name),
                                  swarn->physical,
                                  root, inum, offset,
                                  fs_info->sectorsize, nlink,
                                  (char *)(unsigned long)ipath->fspath->val[i]);

        btrfs_put_root(local_root);
        free_ipath(ipath);
        return 0;

err:
        btrfs_warn_in_rcu(fs_info,
                          "%s at logical %llu on dev %s, physical %llu, root %llu, inode %llu, offset %llu: path resolving failed with ret=%d",
                          swarn->errstr, swarn->logical,
                          rcu_str_deref(swarn->dev->name),
                          swarn->physical,
                          root, inum, offset, ret);

        free_ipath(ipath);
        return 0;
}

static void scrub_print_warning(const char *errstr, struct scrub_block *sblock)
{
        struct btrfs_device *dev;
        struct btrfs_fs_info *fs_info;
        struct btrfs_path *path;
        struct btrfs_key found_key;
        struct extent_buffer *eb;
        struct btrfs_extent_item *ei;
        struct scrub_warning swarn;
        unsigned long ptr = 0;
        u64 extent_item_pos;
        u64 flags = 0;
        u64 ref_root;
        u32 item_size;
        u8 ref_level = 0;
        int ret;

        WARN_ON(sblock->sector_count < 1);
        dev = sblock->dev;
        fs_info = sblock->sctx->fs_info;

        /* Super block error, no need to search extent tree. */
        if (sblock->sectors[0]->flags & BTRFS_EXTENT_FLAG_SUPER) {
                btrfs_warn_in_rcu(fs_info, "%s on device %s, physical %llu",
                        errstr, rcu_str_deref(dev->name),
                        sblock->physical);
                return;
        }
        path = btrfs_alloc_path();
        if (!path)
                return;

        swarn.physical = sblock->physical;
        swarn.logical = sblock->logical;
        swarn.errstr = errstr;
        swarn.dev = NULL;

        ret = extent_from_logical(fs_info, swarn.logical, path, &found_key,
                                  &flags);
        if (ret < 0)
                goto out;

        extent_item_pos = swarn.logical - found_key.objectid;
        swarn.extent_item_size = found_key.offset;

        eb = path->nodes[0];
        ei = btrfs_item_ptr(eb, path->slots[0], struct btrfs_extent_item);
        item_size = btrfs_item_size(eb, path->slots[0]);

        if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
                do {
                        ret = tree_backref_for_extent(&ptr, eb, &found_key, ei,
                                                      item_size, &ref_root,
                                                      &ref_level);
                        btrfs_warn_in_rcu(fs_info,
"%s at logical %llu on dev %s, physical %llu: metadata %s (level %d) in tree %llu",
                                errstr, swarn.logical,
                                rcu_str_deref(dev->name),
                                swarn.physical,
                                ref_level ? "node" : "leaf",
                                ret < 0 ? -1 : ref_level,
                                ret < 0 ? -1 : ref_root);
                } while (ret != 1);
                btrfs_release_path(path);
        } else {
                btrfs_release_path(path);
                swarn.path = path;
                swarn.dev = dev;
                iterate_extent_inodes(fs_info, found_key.objectid,
                                        extent_item_pos, 1,
                                        scrub_print_warning_inode, &swarn, false);
        }

out:
        btrfs_free_path(path);
}

static inline void scrub_get_recover(struct scrub_recover *recover)
{
        refcount_inc(&recover->refs);
}

static inline void scrub_put_recover(struct btrfs_fs_info *fs_info,
                                     struct scrub_recover *recover)
{
        if (refcount_dec_and_test(&recover->refs)) {
                btrfs_bio_counter_dec(fs_info);
                btrfs_put_bioc(recover->bioc);
                kfree(recover);
        }
}

/*
 * scrub_handle_errored_block gets called when either verification of the
 * sectors failed or the bio failed to read, e.g. with EIO. In the latter
 * case, this function handles all sectors in the bio, even though only one
 * may be bad.
 * The goal of this function is to repair the errored block by using the
 * contents of one of the mirrors.
 */
static int scrub_handle_errored_block(struct scrub_block *sblock_to_check)
{
        struct scrub_ctx *sctx = sblock_to_check->sctx;
        struct btrfs_device *dev = sblock_to_check->dev;
        struct btrfs_fs_info *fs_info;
        u64 logical;
        unsigned int failed_mirror_index;
        unsigned int is_metadata;
        unsigned int have_csum;
        /* One scrub_block for each mirror */
        struct scrub_block *sblocks_for_recheck[BTRFS_MAX_MIRRORS] = { 0 };
        struct scrub_block *sblock_bad;
        int ret;
        int mirror_index;
        int sector_num;
        int success;
        bool full_stripe_locked;
        unsigned int nofs_flag;
        static DEFINE_RATELIMIT_STATE(rs, DEFAULT_RATELIMIT_INTERVAL,
                                      DEFAULT_RATELIMIT_BURST);

        BUG_ON(sblock_to_check->sector_count < 1);
        fs_info = sctx->fs_info;
        if (sblock_to_check->sectors[0]->flags & BTRFS_EXTENT_FLAG_SUPER) {
                /*
                 * If we find an error in a super block, we just report it.
                 * They will get written with the next transaction commit
                 * anyway
                 */
                scrub_print_warning("super block error", sblock_to_check);
                spin_lock(&sctx->stat_lock);
                ++sctx->stat.super_errors;
                spin_unlock(&sctx->stat_lock);
                btrfs_dev_stat_inc_and_print(dev, BTRFS_DEV_STAT_CORRUPTION_ERRS);
                return 0;
        }
        logical = sblock_to_check->logical;
        ASSERT(sblock_to_check->mirror_num);
        failed_mirror_index = sblock_to_check->mirror_num - 1;
        is_metadata = !(sblock_to_check->sectors[0]->flags &
                        BTRFS_EXTENT_FLAG_DATA);
        have_csum = sblock_to_check->sectors[0]->have_csum;

        if (!sctx->is_dev_replace && btrfs_repair_one_zone(fs_info, logical))
                return 0;

        /*
         * We must use GFP_NOFS because the scrub task might be waiting for a
         * worker task executing this function and in turn a transaction commit
         * might be waiting the scrub task to pause (which needs to wait for all
         * the worker tasks to complete before pausing).
         * We do allocations in the workers through insert_full_stripe_lock()
         * and scrub_add_sector_to_wr_bio(), which happens down the call chain of
         * this function.
         */
        nofs_flag = memalloc_nofs_save();
        /*
         * For RAID5/6, race can happen for a different device scrub thread.
         * For data corruption, Parity and Data threads will both try
         * to recovery the data.
         * Race can lead to doubly added csum error, or even unrecoverable
         * error.
         */
        ret = lock_full_stripe(fs_info, logical, &full_stripe_locked);
        if (ret < 0) {
                memalloc_nofs_restore(nofs_flag);
                spin_lock(&sctx->stat_lock);
                if (ret == -ENOMEM)
                        sctx->stat.malloc_errors++;
                sctx->stat.read_errors++;
                sctx->stat.uncorrectable_errors++;
                spin_unlock(&sctx->stat_lock);
                return ret;
        }

        /*
         * read all mirrors one after the other. This includes to
         * re-read the extent or metadata block that failed (that was
         * the cause that this fixup code is called) another time,
         * sector by sector this time in order to know which sectors
         * caused I/O errors and which ones are good (for all mirrors).
         * It is the goal to handle the situation when more than one
         * mirror contains I/O errors, but the errors do not
         * overlap, i.e. the data can be repaired by selecting the
         * sectors from those mirrors without I/O error on the
         * particular sectors. One example (with blocks >= 2 * sectorsize)
         * would be that mirror #1 has an I/O error on the first sector,
         * the second sector is good, and mirror #2 has an I/O error on
         * the second sector, but the first sector is good.
         * Then the first sector of the first mirror can be repaired by
         * taking the first sector of the second mirror, and the
         * second sector of the second mirror can be repaired by
         * copying the contents of the 2nd sector of the 1st mirror.
         * One more note: if the sectors of one mirror contain I/O
         * errors, the checksum cannot be verified. In order to get
         * the best data for repairing, the first attempt is to find
         * a mirror without I/O errors and with a validated checksum.
         * Only if this is not possible, the sectors are picked from
         * mirrors with I/O errors without considering the checksum.
         * If the latter is the case, at the end, the checksum of the
         * repaired area is verified in order to correctly maintain
         * the statistics.
         */
        for (mirror_index = 0; mirror_index < BTRFS_MAX_MIRRORS; mirror_index++) {
                /*
                 * Note: the two members refs and outstanding_sectors are not
                 * used in the blocks that are used for the recheck procedure.
                 *
                 * But alloc_scrub_block() will initialize sblock::ref anyway,
                 * so we can use scrub_block_put() to clean them up.
                 *
                 * And here we don't setup the physical/dev for the sblock yet,
                 * they will be correctly initialized in scrub_setup_recheck_block().
                 */
                sblocks_for_recheck[mirror_index] = alloc_scrub_block(sctx, NULL,
                                                        logical, 0, 0, mirror_index);
                if (!sblocks_for_recheck[mirror_index]) {
                        spin_lock(&sctx->stat_lock);
                        sctx->stat.malloc_errors++;
                        sctx->stat.read_errors++;
                        sctx->stat.uncorrectable_errors++;
                        spin_unlock(&sctx->stat_lock);
                        btrfs_dev_stat_inc_and_print(dev, BTRFS_DEV_STAT_READ_ERRS);
                        goto out;
                }
        }

        /* Setup the context, map the logical blocks and alloc the sectors */
        ret = scrub_setup_recheck_block(sblock_to_check, sblocks_for_recheck);
        if (ret) {
                spin_lock(&sctx->stat_lock);
                sctx->stat.read_errors++;
                sctx->stat.uncorrectable_errors++;
                spin_unlock(&sctx->stat_lock);
                btrfs_dev_stat_inc_and_print(dev, BTRFS_DEV_STAT_READ_ERRS);
                goto out;
        }
        BUG_ON(failed_mirror_index >= BTRFS_MAX_MIRRORS);
        sblock_bad = sblocks_for_recheck[failed_mirror_index];

        /* build and submit the bios for the failed mirror, check checksums */
        scrub_recheck_block(fs_info, sblock_bad, 1);

        if (!sblock_bad->header_error && !sblock_bad->checksum_error &&
            sblock_bad->no_io_error_seen) {
                /*
                 * The error disappeared after reading sector by sector, or
                 * the area was part of a huge bio and other parts of the
                 * bio caused I/O errors, or the block layer merged several
                 * read requests into one and the error is caused by a
                 * different bio (usually one of the two latter cases is
                 * the cause)
                 */
                spin_lock(&sctx->stat_lock);
                sctx->stat.unverified_errors++;
                sblock_to_check->data_corrected = 1;
                spin_unlock(&sctx->stat_lock);

                if (sctx->is_dev_replace)
                        scrub_write_block_to_dev_replace(sblock_bad);
                goto out;
        }

        if (!sblock_bad->no_io_error_seen) {
                spin_lock(&sctx->stat_lock);
                sctx->stat.read_errors++;
                spin_unlock(&sctx->stat_lock);
                if (__ratelimit(&rs))
                        scrub_print_warning("i/o error", sblock_to_check);
                btrfs_dev_stat_inc_and_print(dev, BTRFS_DEV_STAT_READ_ERRS);
        } else if (sblock_bad->checksum_error) {
                spin_lock(&sctx->stat_lock);
                sctx->stat.csum_errors++;
                spin_unlock(&sctx->stat_lock);
                if (__ratelimit(&rs))
                        scrub_print_warning("checksum error", sblock_to_check);
                btrfs_dev_stat_inc_and_print(dev,
                                             BTRFS_DEV_STAT_CORRUPTION_ERRS);
        } else if (sblock_bad->header_error) {
                spin_lock(&sctx->stat_lock);
                sctx->stat.verify_errors++;
                spin_unlock(&sctx->stat_lock);
                if (__ratelimit(&rs))
                        scrub_print_warning("checksum/header error",
                                            sblock_to_check);
                if (sblock_bad->generation_error)
                        btrfs_dev_stat_inc_and_print(dev,
                                BTRFS_DEV_STAT_GENERATION_ERRS);
                else
                        btrfs_dev_stat_inc_and_print(dev,
                                BTRFS_DEV_STAT_CORRUPTION_ERRS);
        }

        if (sctx->readonly) {
                ASSERT(!sctx->is_dev_replace);
                goto out;
        }

        /*
         * now build and submit the bios for the other mirrors, check
         * checksums.
         * First try to pick the mirror which is completely without I/O
         * errors and also does not have a checksum error.
         * If one is found, and if a checksum is present, the full block
         * that is known to contain an error is rewritten. Afterwards
         * the block is known to be corrected.
         * If a mirror is found which is completely correct, and no
         * checksum is present, only those sectors are rewritten that had
         * an I/O error in the block to be repaired, since it cannot be
         * determined, which copy of the other sectors is better (and it
         * could happen otherwise that a correct sector would be
         * overwritten by a bad one).
         */
        for (mirror_index = 0; ;mirror_index++) {
                struct scrub_block *sblock_other;

                if (mirror_index == failed_mirror_index)
                        continue;

                /* raid56's mirror can be more than BTRFS_MAX_MIRRORS */
                if (!scrub_is_page_on_raid56(sblock_bad->sectors[0])) {
                        if (mirror_index >= BTRFS_MAX_MIRRORS)
                                break;
                        if (!sblocks_for_recheck[mirror_index]->sector_count)
                                break;

                        sblock_other = sblocks_for_recheck[mirror_index];
                } else {
                        struct scrub_recover *r = sblock_bad->sectors[0]->recover;
                        int max_allowed = r->bioc->num_stripes - r->bioc->num_tgtdevs;

                        if (mirror_index >= max_allowed)
                                break;
                        if (!sblocks_for_recheck[1]->sector_count)
                                break;

                        ASSERT(failed_mirror_index == 0);
                        sblock_other = sblocks_for_recheck[1];
                        sblock_other->mirror_num = 1 + mirror_index;
                }

                /* build and submit the bios, check checksums */
                scrub_recheck_block(fs_info, sblock_other, 0);

                if (!sblock_other->header_error &&
                    !sblock_other->checksum_error &&
                    sblock_other->no_io_error_seen) {
                        if (sctx->is_dev_replace) {
                                scrub_write_block_to_dev_replace(sblock_other);
                                goto corrected_error;
                        } else {
                                ret = scrub_repair_block_from_good_copy(
                                                sblock_bad, sblock_other);
                                if (!ret)
                                        goto corrected_error;
                        }
                }
        }

        if (sblock_bad->no_io_error_seen && !sctx->is_dev_replace)
                goto did_not_correct_error;

        /*
         * In case of I/O errors in the area that is supposed to be
         * repaired, continue by picking good copies of those sectors.
         * Select the good sectors from mirrors to rewrite bad sectors from
         * the area to fix. Afterwards verify the checksum of the block
         * that is supposed to be repaired. This verification step is
         * only done for the purpose of statistic counting and for the
         * final scrub report, whether errors remain.
         * A perfect algorithm could make use of the checksum and try
         * all possible combinations of sectors from the different mirrors
         * until the checksum verification succeeds. For example, when
         * the 2nd sector of mirror #1 faces I/O errors, and the 2nd sector
         * of mirror #2 is readable but the final checksum test fails,
         * then the 2nd sector of mirror #3 could be tried, whether now
         * the final checksum succeeds. But this would be a rare
         * exception and is therefore not implemented. At least it is
         * avoided that the good copy is overwritten.
         * A more useful improvement would be to pick the sectors
         * without I/O error based on sector sizes (512 bytes on legacy
         * disks) instead of on sectorsize. Then maybe 512 byte of one
         * mirror could be repaired by taking 512 byte of a different
         * mirror, even if other 512 byte sectors in the same sectorsize
         * area are unreadable.
         */
        success = 1;
        for (sector_num = 0; sector_num < sblock_bad->sector_count;
             sector_num++) {
                struct scrub_sector *sector_bad = sblock_bad->sectors[sector_num];
                struct scrub_block *sblock_other = NULL;

                /* Skip no-io-error sectors in scrub */
                if (!sector_bad->io_error && !sctx->is_dev_replace)
                        continue;

                if (scrub_is_page_on_raid56(sblock_bad->sectors[0])) {
                        /*
                         * In case of dev replace, if raid56 rebuild process
                         * didn't work out correct data, then copy the content
                         * in sblock_bad to make sure target device is identical
                         * to source device, instead of writing garbage data in
                         * sblock_for_recheck array to target device.
                         */
                        sblock_other = NULL;
                } else if (sector_bad->io_error) {
                        /* Try to find no-io-error sector in mirrors */
                        for (mirror_index = 0;
                             mirror_index < BTRFS_MAX_MIRRORS &&
                             sblocks_for_recheck[mirror_index]->sector_count > 0;
                             mirror_index++) {
                                if (!sblocks_for_recheck[mirror_index]->
                                    sectors[sector_num]->io_error) {
                                        sblock_other = sblocks_for_recheck[mirror_index];
                                        break;
                                }
                        }
                        if (!sblock_other)
                                success = 0;
                }

                if (sctx->is_dev_replace) {
                        /*
                         * Did not find a mirror to fetch the sector from.
                         * scrub_write_sector_to_dev_replace() handles this
                         * case (sector->io_error), by filling the block with
                         * zeros before submitting the write request
                         */
                        if (!sblock_other)
                                sblock_other = sblock_bad;

                        if (scrub_write_sector_to_dev_replace(sblock_other,
                                                              sector_num) != 0) {
                                atomic64_inc(
                                        &fs_info->dev_replace.num_write_errors);
                                success = 0;
                        }
                } else if (sblock_other) {
                        ret = scrub_repair_sector_from_good_copy(sblock_bad,
                                                                 sblock_other,
                                                                 sector_num, 0);
                        if (0 == ret)
                                sector_bad->io_error = 0;
                        else
                                success = 0;
                }
        }

        if (success && !sctx->is_dev_replace) {
                if (is_metadata || have_csum) {
                        /*
                         * need to verify the checksum now that all
                         * sectors on disk are repaired (the write
                         * request for data to be repaired is on its way).
                         * Just be lazy and use scrub_recheck_block()
                         * which re-reads the data before the checksum
                         * is verified, but most likely the data comes out
                         * of the page cache.
                         */
                        scrub_recheck_block(fs_info, sblock_bad, 1);
                        if (!sblock_bad->header_error &&
                            !sblock_bad->checksum_error &&
                            sblock_bad->no_io_error_seen)
                                goto corrected_error;
                        else
                                goto did_not_correct_error;
                } else {
corrected_error:
                        spin_lock(&sctx->stat_lock);
                        sctx->stat.corrected_errors++;
                        sblock_to_check->data_corrected = 1;
                        spin_unlock(&sctx->stat_lock);
                        btrfs_err_rl_in_rcu(fs_info,
                                "fixed up error at logical %llu on dev %s",
                                logical, rcu_str_deref(dev->name));
                }
        } else {
did_not_correct_error:
                spin_lock(&sctx->stat_lock);
                sctx->stat.uncorrectable_errors++;
                spin_unlock(&sctx->stat_lock);
                btrfs_err_rl_in_rcu(fs_info,
                        "unable to fixup (regular) error at logical %llu on dev %s",
                        logical, rcu_str_deref(dev->name));
        }

out:
        for (mirror_index = 0; mirror_index < BTRFS_MAX_MIRRORS; mirror_index++) {
                struct scrub_block *sblock = sblocks_for_recheck[mirror_index];
                struct scrub_recover *recover;
                int sector_index;

                /* Not allocated, continue checking the next mirror */
                if (!sblock)
                        continue;

                for (sector_index = 0; sector_index < sblock->sector_count;
                     sector_index++) {
                        /*
                         * Here we just cleanup the recover, each sector will be
                         * properly cleaned up by later scrub_block_put()
                         */
                        recover = sblock->sectors[sector_index]->recover;
                        if (recover) {
                                scrub_put_recover(fs_info, recover);
                                sblock->sectors[sector_index]->recover = NULL;
                        }
                }
                scrub_block_put(sblock);
        }

        ret = unlock_full_stripe(fs_info, logical, full_stripe_locked);
        memalloc_nofs_restore(nofs_flag);
        if (ret < 0)
                return ret;
        return 0;
}

static inline int scrub_nr_raid_mirrors(struct btrfs_io_context *bioc)
{
        if (bioc->map_type & BTRFS_BLOCK_GROUP_RAID5)
                return 2;
        else if (bioc->map_type & BTRFS_BLOCK_GROUP_RAID6)
                return 3;
        else
                return (int)bioc->num_stripes;
}

static inline void scrub_stripe_index_and_offset(u64 logical, u64 map_type,
                                                 u64 *raid_map,
                                                 int nstripes, int mirror,
                                                 int *stripe_index,
                                                 u64 *stripe_offset)
{
        int i;

        if (map_type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
                /* RAID5/6 */
                for (i = 0; i < nstripes; i++) {
                        if (raid_map[i] == RAID6_Q_STRIPE ||
                            raid_map[i] == RAID5_P_STRIPE)
                                continue;

                        if (logical >= raid_map[i] &&
                            logical < raid_map[i] + BTRFS_STRIPE_LEN)
                                break;
                }

                *stripe_index = i;
                *stripe_offset = logical - raid_map[i];
        } else {
                /* The other RAID type */
                *stripe_index = mirror;
                *stripe_offset = 0;
        }
}

static int scrub_setup_recheck_block(struct scrub_block *original_sblock,
                                     struct scrub_block *sblocks_for_recheck[])
{
        struct scrub_ctx *sctx = original_sblock->sctx;
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        u64 logical = original_sblock->logical;
        u64 length = original_sblock->sector_count << fs_info->sectorsize_bits;
        u64 generation = original_sblock->sectors[0]->generation;
        u64 flags = original_sblock->sectors[0]->flags;
        u64 have_csum = original_sblock->sectors[0]->have_csum;
        struct scrub_recover *recover;
        struct btrfs_io_context *bioc;
        u64 sublen;
        u64 mapped_length;
        u64 stripe_offset;
        int stripe_index;
        int sector_index = 0;
        int mirror_index;
        int nmirrors;
        int ret;

        while (length > 0) {
                sublen = min_t(u64, length, fs_info->sectorsize);
                mapped_length = sublen;
                bioc = NULL;

                /*
                 * With a length of sectorsize, each returned stripe represents
                 * one mirror
                 */
                btrfs_bio_counter_inc_blocked(fs_info);
                ret = btrfs_map_sblock(fs_info, BTRFS_MAP_GET_READ_MIRRORS,
                                       logical, &mapped_length, &bioc);
                if (ret || !bioc || mapped_length < sublen) {
                        btrfs_put_bioc(bioc);
                        btrfs_bio_counter_dec(fs_info);
                        return -EIO;
                }

                recover = kzalloc(sizeof(struct scrub_recover), GFP_NOFS);
                if (!recover) {
                        btrfs_put_bioc(bioc);
                        btrfs_bio_counter_dec(fs_info);
                        return -ENOMEM;
                }

                refcount_set(&recover->refs, 1);
                recover->bioc = bioc;
                recover->map_length = mapped_length;

                ASSERT(sector_index < SCRUB_MAX_SECTORS_PER_BLOCK);

                nmirrors = min(scrub_nr_raid_mirrors(bioc), BTRFS_MAX_MIRRORS);

                for (mirror_index = 0; mirror_index < nmirrors;
                     mirror_index++) {
                        struct scrub_block *sblock;
                        struct scrub_sector *sector;

                        sblock = sblocks_for_recheck[mirror_index];
                        sblock->sctx = sctx;

                        sector = alloc_scrub_sector(sblock, logical, GFP_NOFS);
                        if (!sector) {
                                spin_lock(&sctx->stat_lock);
                                sctx->stat.malloc_errors++;
                                spin_unlock(&sctx->stat_lock);
                                scrub_put_recover(fs_info, recover);
                                return -ENOMEM;
                        }
                        sector->flags = flags;
                        sector->generation = generation;
                        sector->have_csum = have_csum;
                        if (have_csum)
                                memcpy(sector->csum,
                                       original_sblock->sectors[0]->csum,
                                       sctx->fs_info->csum_size);

                        scrub_stripe_index_and_offset(logical,
                                                      bioc->map_type,
                                                      bioc->raid_map,
                                                      bioc->num_stripes -
                                                      bioc->num_tgtdevs,
                                                      mirror_index,
                                                      &stripe_index,
                                                      &stripe_offset);
                        /*
                         * We're at the first sector, also populate @sblock
                         * physical and dev.
                         */
                        if (sector_index == 0) {
                                sblock->physical =
                                        bioc->stripes[stripe_index].physical +
                                        stripe_offset;
                                sblock->dev = bioc->stripes[stripe_index].dev;
                                sblock->physical_for_dev_replace =
                                        original_sblock->physical_for_dev_replace;
                        }

                        BUG_ON(sector_index >= original_sblock->sector_count);
                        scrub_get_recover(recover);
                        sector->recover = recover;
                }
                scrub_put_recover(fs_info, recover);
                length -= sublen;
                logical += sublen;
                sector_index++;
        }

        return 0;
}

static void scrub_bio_wait_endio(struct bio *bio)
{
        complete(bio->bi_private);
}

static int scrub_submit_raid56_bio_wait(struct btrfs_fs_info *fs_info,
                                        struct bio *bio,
                                        struct scrub_sector *sector)
{
        DECLARE_COMPLETION_ONSTACK(done);

        bio->bi_iter.bi_sector = (sector->offset + sector->sblock->logical) >>
                                 SECTOR_SHIFT;
        bio->bi_private = &done;
        bio->bi_end_io = scrub_bio_wait_endio;
        raid56_parity_recover(bio, sector->recover->bioc, sector->sblock->mirror_num);

        wait_for_completion_io(&done);
        return blk_status_to_errno(bio->bi_status);
}

static void scrub_recheck_block_on_raid56(struct btrfs_fs_info *fs_info,
                                          struct scrub_block *sblock)
{
        struct scrub_sector *first_sector = sblock->sectors[0];
        struct bio *bio;
        int i;

        /* All sectors in sblock belong to the same stripe on the same device. */
        ASSERT(sblock->dev);
        if (!sblock->dev->bdev)
                goto out;

        bio = bio_alloc(sblock->dev->bdev, BIO_MAX_VECS, REQ_OP_READ, GFP_NOFS);

        for (i = 0; i < sblock->sector_count; i++) {
                struct scrub_sector *sector = sblock->sectors[i];

                bio_add_scrub_sector(bio, sector, fs_info->sectorsize);
        }

        if (scrub_submit_raid56_bio_wait(fs_info, bio, first_sector)) {
                bio_put(bio);
                goto out;
        }

        bio_put(bio);

        scrub_recheck_block_checksum(sblock);

        return;
out:
        for (i = 0; i < sblock->sector_count; i++)
                sblock->sectors[i]->io_error = 1;

        sblock->no_io_error_seen = 0;
}

/*
 * This function will check the on disk data for checksum errors, header errors
 * and read I/O errors. If any I/O errors happen, the exact sectors which are
 * errored are marked as being bad. The goal is to enable scrub to take those
 * sectors that are not errored from all the mirrors so that the sectors that
 * are errored in the just handled mirror can be repaired.
 */
static void scrub_recheck_block(struct btrfs_fs_info *fs_info,
                                struct scrub_block *sblock,
                                int retry_failed_mirror)
{
        int i;

        sblock->no_io_error_seen = 1;

        /* short cut for raid56 */
        if (!retry_failed_mirror && scrub_is_page_on_raid56(sblock->sectors[0]))
                return scrub_recheck_block_on_raid56(fs_info, sblock);

        for (i = 0; i < sblock->sector_count; i++) {
                struct scrub_sector *sector = sblock->sectors[i];
                struct bio bio;
                struct bio_vec bvec;

                if (sblock->dev->bdev == NULL) {
                        sector->io_error = 1;
                        sblock->no_io_error_seen = 0;
                        continue;
                }

                bio_init(&bio, sblock->dev->bdev, &bvec, 1, REQ_OP_READ);
                bio_add_scrub_sector(&bio, sector, fs_info->sectorsize);
                bio.bi_iter.bi_sector = (sblock->physical + sector->offset) >>
                                        SECTOR_SHIFT;

                btrfsic_check_bio(&bio);
                if (submit_bio_wait(&bio)) {
                        sector->io_error = 1;
                        sblock->no_io_error_seen = 0;
                }

                bio_uninit(&bio);
        }

        if (sblock->no_io_error_seen)
                scrub_recheck_block_checksum(sblock);
}

static inline int scrub_check_fsid(u8 fsid[], struct scrub_sector *sector)
{
        struct btrfs_fs_devices *fs_devices = sector->sblock->dev->fs_devices;
        int ret;

        ret = memcmp(fsid, fs_devices->fsid, BTRFS_FSID_SIZE);
        return !ret;
}

static void scrub_recheck_block_checksum(struct scrub_block *sblock)
{
        sblock->header_error = 0;
        sblock->checksum_error = 0;
        sblock->generation_error = 0;

        if (sblock->sectors[0]->flags & BTRFS_EXTENT_FLAG_DATA)
                scrub_checksum_data(sblock);
        else
                scrub_checksum_tree_block(sblock);
}

static int scrub_repair_block_from_good_copy(struct scrub_block *sblock_bad,
                                             struct scrub_block *sblock_good)
{
        int i;
        int ret = 0;

        for (i = 0; i < sblock_bad->sector_count; i++) {
                int ret_sub;

                ret_sub = scrub_repair_sector_from_good_copy(sblock_bad,
                                                             sblock_good, i, 1);
                if (ret_sub)
                        ret = ret_sub;
        }

        return ret;
}

static int scrub_repair_sector_from_good_copy(struct scrub_block *sblock_bad,
                                              struct scrub_block *sblock_good,
                                              int sector_num, int force_write)
{
        struct scrub_sector *sector_bad = sblock_bad->sectors[sector_num];
        struct scrub_sector *sector_good = sblock_good->sectors[sector_num];
        struct btrfs_fs_info *fs_info = sblock_bad->sctx->fs_info;
        const u32 sectorsize = fs_info->sectorsize;

        if (force_write || sblock_bad->header_error ||
            sblock_bad->checksum_error || sector_bad->io_error) {
                struct bio bio;
                struct bio_vec bvec;
                int ret;

                if (!sblock_bad->dev->bdev) {
                        btrfs_warn_rl(fs_info,
                                "scrub_repair_page_from_good_copy(bdev == NULL) is unexpected");
                        return -EIO;
                }

                bio_init(&bio, sblock_bad->dev->bdev, &bvec, 1, REQ_OP_WRITE);
                bio.bi_iter.bi_sector = (sblock_bad->physical +
                                         sector_bad->offset) >> SECTOR_SHIFT;
                ret = bio_add_scrub_sector(&bio, sector_good, sectorsize);

                btrfsic_check_bio(&bio);
                ret = submit_bio_wait(&bio);
                bio_uninit(&bio);

                if (ret) {
                        btrfs_dev_stat_inc_and_print(sblock_bad->dev,
                                BTRFS_DEV_STAT_WRITE_ERRS);
                        atomic64_inc(&fs_info->dev_replace.num_write_errors);
                        return -EIO;
                }
        }

        return 0;
}

static void scrub_write_block_to_dev_replace(struct scrub_block *sblock)
{
        struct btrfs_fs_info *fs_info = sblock->sctx->fs_info;
        int i;

        /*
         * This block is used for the check of the parity on the source device,
         * so the data needn't be written into the destination device.
         */
        if (sblock->sparity)
                return;

        for (i = 0; i < sblock->sector_count; i++) {
                int ret;

                ret = scrub_write_sector_to_dev_replace(sblock, i);
                if (ret)
                        atomic64_inc(&fs_info->dev_replace.num_write_errors);
        }
}

static int scrub_write_sector_to_dev_replace(struct scrub_block *sblock, int sector_num)
{
        const u32 sectorsize = sblock->sctx->fs_info->sectorsize;
        struct scrub_sector *sector = sblock->sectors[sector_num];

        if (sector->io_error)
                memset(scrub_sector_get_kaddr(sector), 0, sectorsize);

        return scrub_add_sector_to_wr_bio(sblock->sctx, sector);
}

static int fill_writer_pointer_gap(struct scrub_ctx *sctx, u64 physical)
{
        int ret = 0;
        u64 length;

        if (!btrfs_is_zoned(sctx->fs_info))
                return 0;

        if (!btrfs_dev_is_sequential(sctx->wr_tgtdev, physical))
                return 0;

        if (sctx->write_pointer < physical) {
                length = physical - sctx->write_pointer;

                ret = btrfs_zoned_issue_zeroout(sctx->wr_tgtdev,
                                                sctx->write_pointer, length);
                if (!ret)
                        sctx->write_pointer = physical;
        }
        return ret;
}

static void scrub_block_get(struct scrub_block *sblock)
{
        refcount_inc(&sblock->refs);
}

static int scrub_add_sector_to_wr_bio(struct scrub_ctx *sctx,
                                      struct scrub_sector *sector)
{
        struct scrub_block *sblock = sector->sblock;
        struct scrub_bio *sbio;
        int ret;
        const u32 sectorsize = sctx->fs_info->sectorsize;

        mutex_lock(&sctx->wr_lock);
again:
        if (!sctx->wr_curr_bio) {
                sctx->wr_curr_bio = kzalloc(sizeof(*sctx->wr_curr_bio),
                                              GFP_KERNEL);
                if (!sctx->wr_curr_bio) {
                        mutex_unlock(&sctx->wr_lock);
                        return -ENOMEM;
                }
                sctx->wr_curr_bio->sctx = sctx;
                sctx->wr_curr_bio->sector_count = 0;
        }
        sbio = sctx->wr_curr_bio;
        if (sbio->sector_count == 0) {
                ret = fill_writer_pointer_gap(sctx, sector->offset +
                                              sblock->physical_for_dev_replace);
                if (ret) {
                        mutex_unlock(&sctx->wr_lock);
                        return ret;
                }

                sbio->physical = sblock->physical_for_dev_replace + sector->offset;
                sbio->logical = sblock->logical + sector->offset;
                sbio->dev = sctx->wr_tgtdev;
                if (!sbio->bio) {
                        sbio->bio = bio_alloc(sbio->dev->bdev, sctx->sectors_per_bio,
                                              REQ_OP_WRITE, GFP_NOFS);
                }
                sbio->bio->bi_private = sbio;
                sbio->bio->bi_end_io = scrub_wr_bio_end_io;
                sbio->bio->bi_iter.bi_sector = sbio->physical >> 9;
                sbio->status = 0;
        } else if (sbio->physical + sbio->sector_count * sectorsize !=
                   sblock->physical_for_dev_replace + sector->offset ||
                   sbio->logical + sbio->sector_count * sectorsize !=
                   sblock->logical + sector->offset) {
                scrub_wr_submit(sctx);
                goto again;
        }

        ret = bio_add_scrub_sector(sbio->bio, sector, sectorsize);
        if (ret != sectorsize) {
                if (sbio->sector_count < 1) {
                        bio_put(sbio->bio);
                        sbio->bio = NULL;
                        mutex_unlock(&sctx->wr_lock);
                        return -EIO;
                }
                scrub_wr_submit(sctx);
                goto again;
        }

        sbio->sectors[sbio->sector_count] = sector;
        scrub_sector_get(sector);
        /*
         * Since ssector no longer holds a page, but uses sblock::pages, we
         * have to ensure the sblock had not been freed before our write bio
         * finished.
         */
        scrub_block_get(sector->sblock);

        sbio->sector_count++;
        if (sbio->sector_count == sctx->sectors_per_bio)
                scrub_wr_submit(sctx);
        mutex_unlock(&sctx->wr_lock);

        return 0;
}

static void scrub_wr_submit(struct scrub_ctx *sctx)
{
        struct scrub_bio *sbio;

        if (!sctx->wr_curr_bio)
                return;

        sbio = sctx->wr_curr_bio;
        sctx->wr_curr_bio = NULL;
        scrub_pending_bio_inc(sctx);
        /* process all writes in a single worker thread. Then the block layer
         * orders the requests before sending them to the driver which
         * doubled the write performance on spinning disks when measured
         * with Linux 3.5 */
        btrfsic_check_bio(sbio->bio);
        submit_bio(sbio->bio);

        if (btrfs_is_zoned(sctx->fs_info))
                sctx->write_pointer = sbio->physical + sbio->sector_count *
                        sctx->fs_info->sectorsize;
}

static void scrub_wr_bio_end_io(struct bio *bio)
{
        struct scrub_bio *sbio = bio->bi_private;
        struct btrfs_fs_info *fs_info = sbio->dev->fs_info;

        sbio->status = bio->bi_status;
        sbio->bio = bio;

        INIT_WORK(&sbio->work, scrub_wr_bio_end_io_worker);
        queue_work(fs_info->scrub_wr_completion_workers, &sbio->work);
}

static void scrub_wr_bio_end_io_worker(struct work_struct *work)
{
        struct scrub_bio *sbio = container_of(work, struct scrub_bio, work);
        struct scrub_ctx *sctx = sbio->sctx;
        int i;

        ASSERT(sbio->sector_count <= SCRUB_SECTORS_PER_BIO);
        if (sbio->status) {
                struct btrfs_dev_replace *dev_replace =
                        &sbio->sctx->fs_info->dev_replace;

                for (i = 0; i < sbio->sector_count; i++) {
                        struct scrub_sector *sector = sbio->sectors[i];

                        sector->io_error = 1;
                        atomic64_inc(&dev_replace->num_write_errors);
                }
        }

        /*
         * In scrub_add_sector_to_wr_bio() we grab extra ref for sblock, now in
         * endio we should put the sblock.
         */
        for (i = 0; i < sbio->sector_count; i++) {
                scrub_block_put(sbio->sectors[i]->sblock);
                scrub_sector_put(sbio->sectors[i]);
        }

        bio_put(sbio->bio);
        kfree(sbio);
        scrub_pending_bio_dec(sctx);
}

static int scrub_checksum(struct scrub_block *sblock)
{
        u64 flags;
        int ret;

        /*
         * No need to initialize these stats currently,
         * because this function only use return value
         * instead of these stats value.
         *
         * Todo:
         * always use stats
         */
        sblock->header_error = 0;
        sblock->generation_error = 0;
        sblock->checksum_error = 0;

        WARN_ON(sblock->sector_count < 1);
        flags = sblock->sectors[0]->flags;
        ret = 0;
        if (flags & BTRFS_EXTENT_FLAG_DATA)
                ret = scrub_checksum_data(sblock);
        else if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK)
                ret = scrub_checksum_tree_block(sblock);
        else if (flags & BTRFS_EXTENT_FLAG_SUPER)
                ret = scrub_checksum_super(sblock);
        else
                WARN_ON(1);
        if (ret)
                scrub_handle_errored_block(sblock);

        return ret;
}

static int scrub_checksum_data(struct scrub_block *sblock)
{
        struct scrub_ctx *sctx = sblock->sctx;
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
        u8 csum[BTRFS_CSUM_SIZE];
        struct scrub_sector *sector;
        char *kaddr;

        BUG_ON(sblock->sector_count < 1);
        sector = sblock->sectors[0];
        if (!sector->have_csum)
                return 0;

        kaddr = scrub_sector_get_kaddr(sector);

        shash->tfm = fs_info->csum_shash;
        crypto_shash_init(shash);

        crypto_shash_digest(shash, kaddr, fs_info->sectorsize, csum);

        if (memcmp(csum, sector->csum, fs_info->csum_size))
                sblock->checksum_error = 1;
        return sblock->checksum_error;
}

static int scrub_checksum_tree_block(struct scrub_block *sblock)
{
        struct scrub_ctx *sctx = sblock->sctx;
        struct btrfs_header *h;
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
        u8 calculated_csum[BTRFS_CSUM_SIZE];
        u8 on_disk_csum[BTRFS_CSUM_SIZE];
        /*
         * This is done in sectorsize steps even for metadata as there's a
         * constraint for nodesize to be aligned to sectorsize. This will need
         * to change so we don't misuse data and metadata units like that.
         */
        const u32 sectorsize = sctx->fs_info->sectorsize;
        const int num_sectors = fs_info->nodesize >> fs_info->sectorsize_bits;
        int i;
        struct scrub_sector *sector;
        char *kaddr;

        BUG_ON(sblock->sector_count < 1);

        /* Each member in sectors is just one sector */
        ASSERT(sblock->sector_count == num_sectors);

        sector = sblock->sectors[0];
        kaddr = scrub_sector_get_kaddr(sector);
        h = (struct btrfs_header *)kaddr;
        memcpy(on_disk_csum, h->csum, sctx->fs_info->csum_size);

        /*
         * we don't use the getter functions here, as we
         * a) don't have an extent buffer and
         * b) the page is already kmapped
         */
        if (sblock->logical != btrfs_stack_header_bytenr(h)) {
                sblock->header_error = 1;
                btrfs_warn_rl(fs_info,
                "tree block %llu mirror %u has bad bytenr, has %llu want %llu",
                              sblock->logical, sblock->mirror_num,
                              btrfs_stack_header_bytenr(h),
                              sblock->logical);
                goto out;
        }

        if (!scrub_check_fsid(h->fsid, sector)) {
                sblock->header_error = 1;
                btrfs_warn_rl(fs_info,
                "tree block %llu mirror %u has bad fsid, has %pU want %pU",
                              sblock->logical, sblock->mirror_num,
                              h->fsid, sblock->dev->fs_devices->fsid);
                goto out;
        }

        if (memcmp(h->chunk_tree_uuid, fs_info->chunk_tree_uuid, BTRFS_UUID_SIZE)) {
                sblock->header_error = 1;
                btrfs_warn_rl(fs_info,
                "tree block %llu mirror %u has bad chunk tree uuid, has %pU want %pU",
                              sblock->logical, sblock->mirror_num,
                              h->chunk_tree_uuid, fs_info->chunk_tree_uuid);
                goto out;
        }

        shash->tfm = fs_info->csum_shash;
        crypto_shash_init(shash);
        crypto_shash_update(shash, kaddr + BTRFS_CSUM_SIZE,
                            sectorsize - BTRFS_CSUM_SIZE);

        for (i = 1; i < num_sectors; i++) {
                kaddr = scrub_sector_get_kaddr(sblock->sectors[i]);
                crypto_shash_update(shash, kaddr, sectorsize);
        }

        crypto_shash_final(shash, calculated_csum);
        if (memcmp(calculated_csum, on_disk_csum, sctx->fs_info->csum_size)) {
                sblock->checksum_error = 1;
                btrfs_warn_rl(fs_info,
                "tree block %llu mirror %u has bad csum, has " CSUM_FMT " want " CSUM_FMT,
                              sblock->logical, sblock->mirror_num,
                              CSUM_FMT_VALUE(fs_info->csum_size, on_disk_csum),
                              CSUM_FMT_VALUE(fs_info->csum_size, calculated_csum));
                goto out;
        }

        if (sector->generation != btrfs_stack_header_generation(h)) {
                sblock->header_error = 1;
                sblock->generation_error = 1;
                btrfs_warn_rl(fs_info,
                "tree block %llu mirror %u has bad generation, has %llu want %llu",
                              sblock->logical, sblock->mirror_num,
                              btrfs_stack_header_generation(h),
                              sector->generation);
        }

out:
        return sblock->header_error || sblock->checksum_error;
}

static int scrub_checksum_super(struct scrub_block *sblock)
{
        struct btrfs_super_block *s;
        struct scrub_ctx *sctx = sblock->sctx;
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
        u8 calculated_csum[BTRFS_CSUM_SIZE];
        struct scrub_sector *sector;
        char *kaddr;
        int fail_gen = 0;
        int fail_cor = 0;

        BUG_ON(sblock->sector_count < 1);
        sector = sblock->sectors[0];
        kaddr = scrub_sector_get_kaddr(sector);
        s = (struct btrfs_super_block *)kaddr;

        if (sblock->logical != btrfs_super_bytenr(s))
                ++fail_cor;

        if (sector->generation != btrfs_super_generation(s))
                ++fail_gen;

        if (!scrub_check_fsid(s->fsid, sector))
                ++fail_cor;

        shash->tfm = fs_info->csum_shash;
        crypto_shash_init(shash);
        crypto_shash_digest(shash, kaddr + BTRFS_CSUM_SIZE,
                        BTRFS_SUPER_INFO_SIZE - BTRFS_CSUM_SIZE, calculated_csum);

        if (memcmp(calculated_csum, s->csum, sctx->fs_info->csum_size))
                ++fail_cor;

        return fail_cor + fail_gen;
}

static void scrub_block_put(struct scrub_block *sblock)
{
        if (refcount_dec_and_test(&sblock->refs)) {
                int i;

                if (sblock->sparity)
                        scrub_parity_put(sblock->sparity);

                for (i = 0; i < sblock->sector_count; i++)
                        scrub_sector_put(sblock->sectors[i]);
                for (i = 0; i < DIV_ROUND_UP(sblock->len, PAGE_SIZE); i++) {
                        if (sblock->pages[i]) {
                                detach_scrub_page_private(sblock->pages[i]);
                                __free_page(sblock->pages[i]);
                        }
                }
                kfree(sblock);
        }
}

static void scrub_sector_get(struct scrub_sector *sector)
{
        atomic_inc(&sector->refs);
}

static void scrub_sector_put(struct scrub_sector *sector)
{
        if (atomic_dec_and_test(&sector->refs))
                kfree(sector);
}

/*
 * Throttling of IO submission, bandwidth-limit based, the timeslice is 1
 * second.  Limit can be set via /sys/fs/UUID/devinfo/devid/scrub_speed_max.
 */
static void scrub_throttle(struct scrub_ctx *sctx)
{
        const int time_slice = 1000;
        struct scrub_bio *sbio;
        struct btrfs_device *device;
        s64 delta;
        ktime_t now;
        u32 div;
        u64 bwlimit;

        sbio = sctx->bios[sctx->curr];
        device = sbio->dev;
        bwlimit = READ_ONCE(device->scrub_speed_max);
        if (bwlimit == 0)
                return;

        /*
         * Slice is divided into intervals when the IO is submitted, adjust by
         * bwlimit and maximum of 64 intervals.
         */
        div = max_t(u32, 1, (u32)(bwlimit / (16 * 1024 * 1024)));
        div = min_t(u32, 64, div);

        /* Start new epoch, set deadline */
        now = ktime_get();
        if (sctx->throttle_deadline == 0) {
                sctx->throttle_deadline = ktime_add_ms(now, time_slice / div);
                sctx->throttle_sent = 0;
        }

        /* Still in the time to send? */
        if (ktime_before(now, sctx->throttle_deadline)) {
                /* If current bio is within the limit, send it */
                sctx->throttle_sent += sbio->bio->bi_iter.bi_size;
                if (sctx->throttle_sent <= div_u64(bwlimit, div))
                        return;

                /* We're over the limit, sleep until the rest of the slice */
                delta = ktime_ms_delta(sctx->throttle_deadline, now);
        } else {
                /* New request after deadline, start new epoch */
                delta = 0;
        }

        if (delta) {
                long timeout;

                timeout = div_u64(delta * HZ, 1000);
                schedule_timeout_interruptible(timeout);
        }

        /* Next call will start the deadline period */
        sctx->throttle_deadline = 0;
}

static void scrub_submit(struct scrub_ctx *sctx)
{
        struct scrub_bio *sbio;

        if (sctx->curr == -1)
                return;

        scrub_throttle(sctx);

        sbio = sctx->bios[sctx->curr];
        sctx->curr = -1;
        scrub_pending_bio_inc(sctx);
        btrfsic_check_bio(sbio->bio);
        submit_bio(sbio->bio);
}

static int scrub_add_sector_to_rd_bio(struct scrub_ctx *sctx,
                                      struct scrub_sector *sector)
{
        struct scrub_block *sblock = sector->sblock;
        struct scrub_bio *sbio;
        const u32 sectorsize = sctx->fs_info->sectorsize;
        int ret;

again:
        /*
         * grab a fresh bio or wait for one to become available
         */
        while (sctx->curr == -1) {
                spin_lock(&sctx->list_lock);
                sctx->curr = sctx->first_free;
                if (sctx->curr != -1) {
                        sctx->first_free = sctx->bios[sctx->curr]->next_free;
                        sctx->bios[sctx->curr]->next_free = -1;
                        sctx->bios[sctx->curr]->sector_count = 0;
                        spin_unlock(&sctx->list_lock);
                } else {
                        spin_unlock(&sctx->list_lock);
                        wait_event(sctx->list_wait, sctx->first_free != -1);
                }
        }
        sbio = sctx->bios[sctx->curr];
        if (sbio->sector_count == 0) {
                sbio->physical = sblock->physical + sector->offset;
                sbio->logical = sblock->logical + sector->offset;
                sbio->dev = sblock->dev;
                if (!sbio->bio) {
                        sbio->bio = bio_alloc(sbio->dev->bdev, sctx->sectors_per_bio,
                                              REQ_OP_READ, GFP_NOFS);
                }
                sbio->bio->bi_private = sbio;
                sbio->bio->bi_end_io = scrub_bio_end_io;
                sbio->bio->bi_iter.bi_sector = sbio->physical >> 9;
                sbio->status = 0;
        } else if (sbio->physical + sbio->sector_count * sectorsize !=
                   sblock->physical + sector->offset ||
                   sbio->logical + sbio->sector_count * sectorsize !=
                   sblock->logical + sector->offset ||
                   sbio->dev != sblock->dev) {
                scrub_submit(sctx);
                goto again;
        }

        sbio->sectors[sbio->sector_count] = sector;
        ret = bio_add_scrub_sector(sbio->bio, sector, sectorsize);
        if (ret != sectorsize) {
                if (sbio->sector_count < 1) {
                        bio_put(sbio->bio);
                        sbio->bio = NULL;
                        return -EIO;
                }
                scrub_submit(sctx);
                goto again;
        }

        scrub_block_get(sblock); /* one for the page added to the bio */
        atomic_inc(&sblock->outstanding_sectors);
        sbio->sector_count++;
        if (sbio->sector_count == sctx->sectors_per_bio)
                scrub_submit(sctx);

        return 0;
}

static void scrub_missing_raid56_end_io(struct bio *bio)
{
        struct scrub_block *sblock = bio->bi_private;
        struct btrfs_fs_info *fs_info = sblock->sctx->fs_info;

        btrfs_bio_counter_dec(fs_info);
        if (bio->bi_status)
                sblock->no_io_error_seen = 0;

        bio_put(bio);

        queue_work(fs_info->scrub_workers, &sblock->work);
}

static void scrub_missing_raid56_worker(struct work_struct *work)
{
        struct scrub_block *sblock = container_of(work, struct scrub_block, work);
        struct scrub_ctx *sctx = sblock->sctx;
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        u64 logical;
        struct btrfs_device *dev;

        logical = sblock->logical;
        dev = sblock->dev;

        if (sblock->no_io_error_seen)
                scrub_recheck_block_checksum(sblock);

        if (!sblock->no_io_error_seen) {
                spin_lock(&sctx->stat_lock);
                sctx->stat.read_errors++;
                spin_unlock(&sctx->stat_lock);
                btrfs_err_rl_in_rcu(fs_info,
                        "IO error rebuilding logical %llu for dev %s",
                        logical, rcu_str_deref(dev->name));
        } else if (sblock->header_error || sblock->checksum_error) {
                spin_lock(&sctx->stat_lock);
                sctx->stat.uncorrectable_errors++;
                spin_unlock(&sctx->stat_lock);
                btrfs_err_rl_in_rcu(fs_info,
                        "failed to rebuild valid logical %llu for dev %s",
                        logical, rcu_str_deref(dev->name));
        } else {
                scrub_write_block_to_dev_replace(sblock);
        }

        if (sctx->is_dev_replace && sctx->flush_all_writes) {
                mutex_lock(&sctx->wr_lock);
                scrub_wr_submit(sctx);
                mutex_unlock(&sctx->wr_lock);
        }

        scrub_block_put(sblock);
        scrub_pending_bio_dec(sctx);
}

static void scrub_missing_raid56_pages(struct scrub_block *sblock)
{
        struct scrub_ctx *sctx = sblock->sctx;
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        u64 length = sblock->sector_count << fs_info->sectorsize_bits;
        u64 logical = sblock->logical;
        struct btrfs_io_context *bioc = NULL;
        struct bio *bio;
        struct btrfs_raid_bio *rbio;
        int ret;
        int i;

        btrfs_bio_counter_inc_blocked(fs_info);
        ret = btrfs_map_sblock(fs_info, BTRFS_MAP_GET_READ_MIRRORS, logical,
                               &length, &bioc);
        if (ret || !bioc || !bioc->raid_map)
                goto bioc_out;

        if (WARN_ON(!sctx->is_dev_replace ||
                    !(bioc->map_type & BTRFS_BLOCK_GROUP_RAID56_MASK))) {
                /*
                 * We shouldn't be scrubbing a missing device. Even for dev
                 * replace, we should only get here for RAID 5/6. We either
                 * managed to mount something with no mirrors remaining or
                 * there's a bug in scrub_find_good_copy()/btrfs_map_block().
                 */
                goto bioc_out;
        }

        bio = bio_alloc(NULL, BIO_MAX_VECS, REQ_OP_READ, GFP_NOFS);
        bio->bi_iter.bi_sector = logical >> 9;
        bio->bi_private = sblock;
        bio->bi_end_io = scrub_missing_raid56_end_io;

        rbio = raid56_alloc_missing_rbio(bio, bioc);
        if (!rbio)
                goto rbio_out;

        for (i = 0; i < sblock->sector_count; i++) {
                struct scrub_sector *sector = sblock->sectors[i];

                raid56_add_scrub_pages(rbio, scrub_sector_get_page(sector),
                                       scrub_sector_get_page_offset(sector),
                                       sector->offset + sector->sblock->logical);
        }

        INIT_WORK(&sblock->work, scrub_missing_raid56_worker);
        scrub_block_get(sblock);
        scrub_pending_bio_inc(sctx);
        raid56_submit_missing_rbio(rbio);
        btrfs_put_bioc(bioc);
        return;

rbio_out:
        bio_put(bio);
bioc_out:
        btrfs_bio_counter_dec(fs_info);
        btrfs_put_bioc(bioc);
        spin_lock(&sctx->stat_lock);
        sctx->stat.malloc_errors++;
        spin_unlock(&sctx->stat_lock);
}

static int scrub_sectors(struct scrub_ctx *sctx, u64 logical, u32 len,
                       u64 physical, struct btrfs_device *dev, u64 flags,
                       u64 gen, int mirror_num, u8 *csum,
                       u64 physical_for_dev_replace)
{
        struct scrub_block *sblock;
        const u32 sectorsize = sctx->fs_info->sectorsize;
        int index;

        sblock = alloc_scrub_block(sctx, dev, logical, physical,
                                   physical_for_dev_replace, mirror_num);
        if (!sblock) {
                spin_lock(&sctx->stat_lock);
                sctx->stat.malloc_errors++;
                spin_unlock(&sctx->stat_lock);
                return -ENOMEM;
        }

        for (index = 0; len > 0; index++) {
                struct scrub_sector *sector;
                /*
                 * Here we will allocate one page for one sector to scrub.
                 * This is fine if PAGE_SIZE == sectorsize, but will cost
                 * more memory for PAGE_SIZE > sectorsize case.
                 */
                u32 l = min(sectorsize, len);

                sector = alloc_scrub_sector(sblock, logical, GFP_KERNEL);
                if (!sector) {
                        spin_lock(&sctx->stat_lock);
                        sctx->stat.malloc_errors++;
                        spin_unlock(&sctx->stat_lock);
                        scrub_block_put(sblock);
                        return -ENOMEM;
                }
                sector->flags = flags;
                sector->generation = gen;
                if (csum) {
                        sector->have_csum = 1;
                        memcpy(sector->csum, csum, sctx->fs_info->csum_size);
                } else {
                        sector->have_csum = 0;
                }
                len -= l;
                logical += l;
                physical += l;
                physical_for_dev_replace += l;
        }

        WARN_ON(sblock->sector_count == 0);
        if (test_bit(BTRFS_DEV_STATE_MISSING, &dev->dev_state)) {
                /*
                 * This case should only be hit for RAID 5/6 device replace. See
                 * the comment in scrub_missing_raid56_pages() for details.
                 */
                scrub_missing_raid56_pages(sblock);
        } else {
                for (index = 0; index < sblock->sector_count; index++) {
                        struct scrub_sector *sector = sblock->sectors[index];
                        int ret;

                        ret = scrub_add_sector_to_rd_bio(sctx, sector);
                        if (ret) {
                                scrub_block_put(sblock);
                                return ret;
                        }
                }

                if (flags & BTRFS_EXTENT_FLAG_SUPER)
                        scrub_submit(sctx);
        }

        /* last one frees, either here or in bio completion for last page */
        scrub_block_put(sblock);
        return 0;
}

static void scrub_bio_end_io(struct bio *bio)
{
        struct scrub_bio *sbio = bio->bi_private;
        struct btrfs_fs_info *fs_info = sbio->dev->fs_info;

        sbio->status = bio->bi_status;
        sbio->bio = bio;

        queue_work(fs_info->scrub_workers, &sbio->work);
}

static void scrub_bio_end_io_worker(struct work_struct *work)
{
        struct scrub_bio *sbio = container_of(work, struct scrub_bio, work);
        struct scrub_ctx *sctx = sbio->sctx;
        int i;

        ASSERT(sbio->sector_count <= SCRUB_SECTORS_PER_BIO);
        if (sbio->status) {
                for (i = 0; i < sbio->sector_count; i++) {
                        struct scrub_sector *sector = sbio->sectors[i];

                        sector->io_error = 1;
                        sector->sblock->no_io_error_seen = 0;
                }
        }

        /* Now complete the scrub_block items that have all pages completed */
        for (i = 0; i < sbio->sector_count; i++) {
                struct scrub_sector *sector = sbio->sectors[i];
                struct scrub_block *sblock = sector->sblock;

                if (atomic_dec_and_test(&sblock->outstanding_sectors))
                        scrub_block_complete(sblock);
                scrub_block_put(sblock);
        }

        bio_put(sbio->bio);
        sbio->bio = NULL;
        spin_lock(&sctx->list_lock);
        sbio->next_free = sctx->first_free;
        sctx->first_free = sbio->index;
        spin_unlock(&sctx->list_lock);

        if (sctx->is_dev_replace && sctx->flush_all_writes) {
                mutex_lock(&sctx->wr_lock);
                scrub_wr_submit(sctx);
                mutex_unlock(&sctx->wr_lock);
        }

        scrub_pending_bio_dec(sctx);
}

static inline void __scrub_mark_bitmap(struct scrub_parity *sparity,
                                       unsigned long *bitmap,
                                       u64 start, u32 len)
{
        u64 offset;
        u32 nsectors;
        u32 sectorsize_bits = sparity->sctx->fs_info->sectorsize_bits;

        if (len >= sparity->stripe_len) {
                bitmap_set(bitmap, 0, sparity->nsectors);
                return;
        }

        start -= sparity->logic_start;
        start = div64_u64_rem(start, sparity->stripe_len, &offset);
        offset = offset >> sectorsize_bits;
        nsectors = len >> sectorsize_bits;

        if (offset + nsectors <= sparity->nsectors) {
                bitmap_set(bitmap, offset, nsectors);
                return;
        }

        bitmap_set(bitmap, offset, sparity->nsectors - offset);
        bitmap_set(bitmap, 0, nsectors - (sparity->nsectors - offset));
}

static inline void scrub_parity_mark_sectors_error(struct scrub_parity *sparity,
                                                   u64 start, u32 len)
{
        __scrub_mark_bitmap(sparity, &sparity->ebitmap, start, len);
}

static inline void scrub_parity_mark_sectors_data(struct scrub_parity *sparity,
                                                  u64 start, u32 len)
{
        __scrub_mark_bitmap(sparity, &sparity->dbitmap, start, len);
}

static void scrub_block_complete(struct scrub_block *sblock)
{
        int corrupted = 0;

        if (!sblock->no_io_error_seen) {
                corrupted = 1;
                scrub_handle_errored_block(sblock);
        } else {
                /*
                 * if has checksum error, write via repair mechanism in
                 * dev replace case, otherwise write here in dev replace
                 * case.
                 */
                corrupted = scrub_checksum(sblock);
                if (!corrupted && sblock->sctx->is_dev_replace)
                        scrub_write_block_to_dev_replace(sblock);
        }

        if (sblock->sparity && corrupted && !sblock->data_corrected) {
                u64 start = sblock->logical;
                u64 end = sblock->logical +
                          sblock->sectors[sblock->sector_count - 1]->offset +
                          sblock->sctx->fs_info->sectorsize;

                ASSERT(end - start <= U32_MAX);
                scrub_parity_mark_sectors_error(sblock->sparity,
                                                start, end - start);
        }
}

static void drop_csum_range(struct scrub_ctx *sctx, struct btrfs_ordered_sum *sum)
{
        sctx->stat.csum_discards += sum->len >> sctx->fs_info->sectorsize_bits;
        list_del(&sum->list);
        kfree(sum);
}

/*
 * Find the desired csum for range [logical, logical + sectorsize), and store
 * the csum into @csum.
 *
 * The search source is sctx->csum_list, which is a pre-populated list
 * storing bytenr ordered csum ranges.  We're responsible to cleanup any range
 * that is before @logical.
 *
 * Return 0 if there is no csum for the range.
 * Return 1 if there is csum for the range and copied to @csum.
 */
static int scrub_find_csum(struct scrub_ctx *sctx, u64 logical, u8 *csum)
{
        bool found = false;

        while (!list_empty(&sctx->csum_list)) {
                struct btrfs_ordered_sum *sum = NULL;
                unsigned long index;
                unsigned long num_sectors;

                sum = list_first_entry(&sctx->csum_list,
                                       struct btrfs_ordered_sum, list);
                /* The current csum range is beyond our range, no csum found */
                if (sum->bytenr > logical)
                        break;

                /*
                 * The current sum is before our bytenr, since scrub is always
                 * done in bytenr order, the csum will never be used anymore,
                 * clean it up so that later calls won't bother with the range,
                 * and continue search the next range.
                 */
                if (sum->bytenr + sum->len <= logical) {
                        drop_csum_range(sctx, sum);
                        continue;
                }

                /* Now the csum range covers our bytenr, copy the csum */
                found = true;
                index = (logical - sum->bytenr) >> sctx->fs_info->sectorsize_bits;
                num_sectors = sum->len >> sctx->fs_info->sectorsize_bits;

                memcpy(csum, sum->sums + index * sctx->fs_info->csum_size,
                       sctx->fs_info->csum_size);

                /* Cleanup the range if we're at the end of the csum range */
                if (index == num_sectors - 1)
                        drop_csum_range(sctx, sum);
                break;
        }
        if (!found)
                return 0;
        return 1;
}

/* scrub extent tries to collect up to 64 kB for each bio */
static int scrub_extent(struct scrub_ctx *sctx, struct map_lookup *map,
                        u64 logical, u32 len,
                        u64 physical, struct btrfs_device *dev, u64 flags,
                        u64 gen, int mirror_num)
{
        struct btrfs_device *src_dev = dev;
        u64 src_physical = physical;
        int src_mirror = mirror_num;
        int ret;
        u8 csum[BTRFS_CSUM_SIZE];
        u32 blocksize;

        if (flags & BTRFS_EXTENT_FLAG_DATA) {
                if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK)
                        blocksize = map->stripe_len;
                else
                        blocksize = sctx->fs_info->sectorsize;
                spin_lock(&sctx->stat_lock);
                sctx->stat.data_extents_scrubbed++;
                sctx->stat.data_bytes_scrubbed += len;
                spin_unlock(&sctx->stat_lock);
        } else if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
                if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK)
                        blocksize = map->stripe_len;
                else
                        blocksize = sctx->fs_info->nodesize;
                spin_lock(&sctx->stat_lock);
                sctx->stat.tree_extents_scrubbed++;
                sctx->stat.tree_bytes_scrubbed += len;
                spin_unlock(&sctx->stat_lock);
        } else {
                blocksize = sctx->fs_info->sectorsize;
                WARN_ON(1);
        }

        /*
         * For dev-replace case, we can have @dev being a missing device.
         * Regular scrub will avoid its execution on missing device at all,
         * as that would trigger tons of read error.
         *
         * Reading from missing device will cause read error counts to
         * increase unnecessarily.
         * So here we change the read source to a good mirror.
         */
        if (sctx->is_dev_replace && !dev->bdev)
                scrub_find_good_copy(sctx->fs_info, logical, len, &src_physical,
                                     &src_dev, &src_mirror);
        while (len) {
                u32 l = min(len, blocksize);
                int have_csum = 0;

                if (flags & BTRFS_EXTENT_FLAG_DATA) {
                        /* push csums to sbio */
                        have_csum = scrub_find_csum(sctx, logical, csum);
                        if (have_csum == 0)
                                ++sctx->stat.no_csum;
                }
                ret = scrub_sectors(sctx, logical, l, src_physical, src_dev,
                                    flags, gen, src_mirror,
                                    have_csum ? csum : NULL, physical);
                if (ret)
                        return ret;
                len -= l;
                logical += l;
                physical += l;
                src_physical += l;
        }
        return 0;
}

static int scrub_sectors_for_parity(struct scrub_parity *sparity,
                                  u64 logical, u32 len,
                                  u64 physical, struct btrfs_device *dev,
                                  u64 flags, u64 gen, int mirror_num, u8 *csum)
{
        struct scrub_ctx *sctx = sparity->sctx;
        struct scrub_block *sblock;
        const u32 sectorsize = sctx->fs_info->sectorsize;
        int index;

        ASSERT(IS_ALIGNED(len, sectorsize));

        sblock = alloc_scrub_block(sctx, dev, logical, physical, physical, mirror_num);
        if (!sblock) {
                spin_lock(&sctx->stat_lock);
                sctx->stat.malloc_errors++;
                spin_unlock(&sctx->stat_lock);
                return -ENOMEM;
        }

        sblock->sparity = sparity;
        scrub_parity_get(sparity);

        for (index = 0; len > 0; index++) {
                struct scrub_sector *sector;

                sector = alloc_scrub_sector(sblock, logical, GFP_KERNEL);
                if (!sector) {
                        spin_lock(&sctx->stat_lock);
                        sctx->stat.malloc_errors++;
                        spin_unlock(&sctx->stat_lock);
                        scrub_block_put(sblock);
                        return -ENOMEM;
                }
                sblock->sectors[index] = sector;
                /* For scrub parity */
                scrub_sector_get(sector);
                list_add_tail(&sector->list, &sparity->sectors_list);
                sector->flags = flags;
                sector->generation = gen;
                if (csum) {
                        sector->have_csum = 1;
                        memcpy(sector->csum, csum, sctx->fs_info->csum_size);
                } else {
                        sector->have_csum = 0;
                }

                /* Iterate over the stripe range in sectorsize steps */
                len -= sectorsize;
                logical += sectorsize;
                physical += sectorsize;
        }

        WARN_ON(sblock->sector_count == 0);
        for (index = 0; index < sblock->sector_count; index++) {
                struct scrub_sector *sector = sblock->sectors[index];
                int ret;

                ret = scrub_add_sector_to_rd_bio(sctx, sector);
                if (ret) {
                        scrub_block_put(sblock);
                        return ret;
                }
        }

        /* Last one frees, either here or in bio completion for last sector */
        scrub_block_put(sblock);
        return 0;
}

static int scrub_extent_for_parity(struct scrub_parity *sparity,
                                   u64 logical, u32 len,
                                   u64 physical, struct btrfs_device *dev,
                                   u64 flags, u64 gen, int mirror_num)
{
        struct scrub_ctx *sctx = sparity->sctx;
        int ret;
        u8 csum[BTRFS_CSUM_SIZE];
        u32 blocksize;

        if (test_bit(BTRFS_DEV_STATE_MISSING, &dev->dev_state)) {
                scrub_parity_mark_sectors_error(sparity, logical, len);
                return 0;
        }

        if (flags & BTRFS_EXTENT_FLAG_DATA) {
                blocksize = sparity->stripe_len;
        } else if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
                blocksize = sparity->stripe_len;
        } else {
                blocksize = sctx->fs_info->sectorsize;
                WARN_ON(1);
        }

        while (len) {
                u32 l = min(len, blocksize);
                int have_csum = 0;

                if (flags & BTRFS_EXTENT_FLAG_DATA) {
                        /* push csums to sbio */
                        have_csum = scrub_find_csum(sctx, logical, csum);
                        if (have_csum == 0)
                                goto skip;
                }
                ret = scrub_sectors_for_parity(sparity, logical, l, physical, dev,
                                             flags, gen, mirror_num,
                                             have_csum ? csum : NULL);
                if (ret)
                        return ret;
skip:
                len -= l;
                logical += l;
                physical += l;
        }
        return 0;
}

/*
 * Given a physical address, this will calculate it's
 * logical offset. if this is a parity stripe, it will return
 * the most left data stripe's logical offset.
 *
 * return 0 if it is a data stripe, 1 means parity stripe.
 */
static int get_raid56_logic_offset(u64 physical, int num,
                                   struct map_lookup *map, u64 *offset,
                                   u64 *stripe_start)
{
        int i;
        int j = 0;
        u64 stripe_nr;
        u64 last_offset;
        u32 stripe_index;
        u32 rot;
        const int data_stripes = nr_data_stripes(map);

        last_offset = (physical - map->stripes[num].physical) * data_stripes;
        if (stripe_start)
                *stripe_start = last_offset;

        *offset = last_offset;
        for (i = 0; i < data_stripes; i++) {
                *offset = last_offset + i * map->stripe_len;

                stripe_nr = div64_u64(*offset, map->stripe_len);
                stripe_nr = div_u64(stripe_nr, data_stripes);

                /* Work out the disk rotation on this stripe-set */
                stripe_nr = div_u64_rem(stripe_nr, map->num_stripes, &rot);
                /* calculate which stripe this data locates */
                rot += i;
                stripe_index = rot % map->num_stripes;
                if (stripe_index == num)
                        return 0;
                if (stripe_index < num)
                        j++;
        }
        *offset = last_offset + j * map->stripe_len;
        return 1;
}

static void scrub_free_parity(struct scrub_parity *sparity)
{
        struct scrub_ctx *sctx = sparity->sctx;
        struct scrub_sector *curr, *next;
        int nbits;

        nbits = bitmap_weight(&sparity->ebitmap, sparity->nsectors);
        if (nbits) {
                spin_lock(&sctx->stat_lock);
                sctx->stat.read_errors += nbits;
                sctx->stat.uncorrectable_errors += nbits;
                spin_unlock(&sctx->stat_lock);
        }

        list_for_each_entry_safe(curr, next, &sparity->sectors_list, list) {
                list_del_init(&curr->list);
                scrub_sector_put(curr);
        }

        kfree(sparity);
}

static void scrub_parity_bio_endio_worker(struct work_struct *work)
{
        struct scrub_parity *sparity = container_of(work, struct scrub_parity,
                                                    work);
        struct scrub_ctx *sctx = sparity->sctx;

        btrfs_bio_counter_dec(sctx->fs_info);
        scrub_free_parity(sparity);
        scrub_pending_bio_dec(sctx);
}

static void scrub_parity_bio_endio(struct bio *bio)
{
        struct scrub_parity *sparity = bio->bi_private;
        struct btrfs_fs_info *fs_info = sparity->sctx->fs_info;

        if (bio->bi_status)
                bitmap_or(&sparity->ebitmap, &sparity->ebitmap,
                          &sparity->dbitmap, sparity->nsectors);

        bio_put(bio);

        INIT_WORK(&sparity->work, scrub_parity_bio_endio_worker);
        queue_work(fs_info->scrub_parity_workers, &sparity->work);
}

static void scrub_parity_check_and_repair(struct scrub_parity *sparity)
{
        struct scrub_ctx *sctx = sparity->sctx;
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        struct bio *bio;
        struct btrfs_raid_bio *rbio;
        struct btrfs_io_context *bioc = NULL;
        u64 length;
        int ret;

        if (!bitmap_andnot(&sparity->dbitmap, &sparity->dbitmap,
                           &sparity->ebitmap, sparity->nsectors))
                goto out;

        length = sparity->logic_end - sparity->logic_start;

        btrfs_bio_counter_inc_blocked(fs_info);
        ret = btrfs_map_sblock(fs_info, BTRFS_MAP_WRITE, sparity->logic_start,
                               &length, &bioc);
        if (ret || !bioc || !bioc->raid_map)
                goto bioc_out;

        bio = bio_alloc(NULL, BIO_MAX_VECS, REQ_OP_READ, GFP_NOFS);
        bio->bi_iter.bi_sector = sparity->logic_start >> 9;
        bio->bi_private = sparity;
        bio->bi_end_io = scrub_parity_bio_endio;

        rbio = raid56_parity_alloc_scrub_rbio(bio, bioc,
                                              sparity->scrub_dev,
                                              &sparity->dbitmap,
                                              sparity->nsectors);
        btrfs_put_bioc(bioc);
        if (!rbio)
                goto rbio_out;

        scrub_pending_bio_inc(sctx);
        raid56_parity_submit_scrub_rbio(rbio);
        return;

rbio_out:
        bio_put(bio);
bioc_out:
        btrfs_bio_counter_dec(fs_info);
        bitmap_or(&sparity->ebitmap, &sparity->ebitmap, &sparity->dbitmap,
                  sparity->nsectors);
        spin_lock(&sctx->stat_lock);
        sctx->stat.malloc_errors++;
        spin_unlock(&sctx->stat_lock);
out:
        scrub_free_parity(sparity);
}

static void scrub_parity_get(struct scrub_parity *sparity)
{
        refcount_inc(&sparity->refs);
}

static void scrub_parity_put(struct scrub_parity *sparity)
{
        if (!refcount_dec_and_test(&sparity->refs))
                return;

        scrub_parity_check_and_repair(sparity);
}

/*
 * Return 0 if the extent item range covers any byte of the range.
 * Return <0 if the extent item is before @search_start.
 * Return >0 if the extent item is after @start_start + @search_len.
 */
static int compare_extent_item_range(struct btrfs_path *path,
                                     u64 search_start, u64 search_len)
{
        struct btrfs_fs_info *fs_info = path->nodes[0]->fs_info;
        u64 len;
        struct btrfs_key key;

        btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
        ASSERT(key.type == BTRFS_EXTENT_ITEM_KEY ||
               key.type == BTRFS_METADATA_ITEM_KEY);
        if (key.type == BTRFS_METADATA_ITEM_KEY)
                len = fs_info->nodesize;
        else
                len = key.offset;

        if (key.objectid + len <= search_start)
                return -1;
        if (key.objectid >= search_start + search_len)
                return 1;
        return 0;
}

/*
 * Locate one extent item which covers any byte in range
 * [@search_start, @search_start + @search_length)
 *
 * If the path is not initialized, we will initialize the search by doing
 * a btrfs_search_slot().
 * If the path is already initialized, we will use the path as the initial
 * slot, to avoid duplicated btrfs_search_slot() calls.
 *
 * NOTE: If an extent item starts before @search_start, we will still
 * return the extent item. This is for data extent crossing stripe boundary.
 *
 * Return 0 if we found such extent item, and @path will point to the extent item.
 * Return >0 if no such extent item can be found, and @path will be released.
 * Return <0 if hit fatal error, and @path will be released.
 */
static int find_first_extent_item(struct btrfs_root *extent_root,
                                  struct btrfs_path *path,
                                  u64 search_start, u64 search_len)
{
        struct btrfs_fs_info *fs_info = extent_root->fs_info;
        struct btrfs_key key;
        int ret;

        /* Continue using the existing path */
        if (path->nodes[0])
                goto search_forward;

        if (btrfs_fs_incompat(fs_info, SKINNY_METADATA))
                key.type = BTRFS_METADATA_ITEM_KEY;
        else
                key.type = BTRFS_EXTENT_ITEM_KEY;
        key.objectid = search_start;
        key.offset = (u64)-1;

        ret = btrfs_search_slot(NULL, extent_root, &key, path, 0, 0);
        if (ret < 0)
                return ret;

        ASSERT(ret > 0);
        /*
         * Here we intentionally pass 0 as @min_objectid, as there could be
         * an extent item starting before @search_start.
         */
        ret = btrfs_previous_extent_item(extent_root, path, 0);
        if (ret < 0)
                return ret;
        /*
         * No matter whether we have found an extent item, the next loop will
         * properly do every check on the key.
         */
search_forward:
        while (true) {
                btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
                if (key.objectid >= search_start + search_len)
                        break;
                if (key.type != BTRFS_METADATA_ITEM_KEY &&
                    key.type != BTRFS_EXTENT_ITEM_KEY)
                        goto next;

                ret = compare_extent_item_range(path, search_start, search_len);
                if (ret == 0)
                        return ret;
                if (ret > 0)
                        break;
next:
                path->slots[0]++;
                if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
                        ret = btrfs_next_leaf(extent_root, path);
                        if (ret) {
                                /* Either no more item or fatal error */
                                btrfs_release_path(path);
                                return ret;
                        }
                }
        }
        btrfs_release_path(path);
        return 1;
}

static void get_extent_info(struct btrfs_path *path, u64 *extent_start_ret,
                            u64 *size_ret, u64 *flags_ret, u64 *generation_ret)
{
        struct btrfs_key key;
        struct btrfs_extent_item *ei;

        btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
        ASSERT(key.type == BTRFS_METADATA_ITEM_KEY ||
               key.type == BTRFS_EXTENT_ITEM_KEY);
        *extent_start_ret = key.objectid;
        if (key.type == BTRFS_METADATA_ITEM_KEY)
                *size_ret = path->nodes[0]->fs_info->nodesize;
        else
                *size_ret = key.offset;
        ei = btrfs_item_ptr(path->nodes[0], path->slots[0], struct btrfs_extent_item);
        *flags_ret = btrfs_extent_flags(path->nodes[0], ei);
        *generation_ret = btrfs_extent_generation(path->nodes[0], ei);
}

static bool does_range_cross_boundary(u64 extent_start, u64 extent_len,
                                      u64 boundary_start, u64 boudary_len)
{
        return (extent_start < boundary_start &&
                extent_start + extent_len > boundary_start) ||
               (extent_start < boundary_start + boudary_len &&
                extent_start + extent_len > boundary_start + boudary_len);
}

static int scrub_raid56_data_stripe_for_parity(struct scrub_ctx *sctx,
                                               struct scrub_parity *sparity,
                                               struct map_lookup *map,
                                               struct btrfs_device *sdev,
                                               struct btrfs_path *path,
                                               u64 logical)
{
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        struct btrfs_root *extent_root = btrfs_extent_root(fs_info, logical);
        struct btrfs_root *csum_root = btrfs_csum_root(fs_info, logical);
        u64 cur_logical = logical;
        int ret;

        ASSERT(map->type & BTRFS_BLOCK_GROUP_RAID56_MASK);

        /* Path must not be populated */
        ASSERT(!path->nodes[0]);

        while (cur_logical < logical + map->stripe_len) {
                struct btrfs_io_context *bioc = NULL;
                struct btrfs_device *extent_dev;
                u64 extent_start;
                u64 extent_size;
                u64 mapped_length;
                u64 extent_flags;
                u64 extent_gen;
                u64 extent_physical;
                u64 extent_mirror_num;

                ret = find_first_extent_item(extent_root, path, cur_logical,
                                             logical + map->stripe_len - cur_logical);
                /* No more extent item in this data stripe */
                if (ret > 0) {
                        ret = 0;
                        break;
                }
                if (ret < 0)
                        break;
                get_extent_info(path, &extent_start, &extent_size, &extent_flags,
                                &extent_gen);

                /* Metadata should not cross stripe boundaries */
                if ((extent_flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) &&
                    does_range_cross_boundary(extent_start, extent_size,
                                              logical, map->stripe_len)) {
                        btrfs_err(fs_info,
        "scrub: tree block %llu spanning stripes, ignored. logical=%llu",
                                  extent_start, logical);
                        spin_lock(&sctx->stat_lock);
                        sctx->stat.uncorrectable_errors++;
                        spin_unlock(&sctx->stat_lock);
                        cur_logical += extent_size;
                        continue;
                }

                /* Skip hole range which doesn't have any extent */
                cur_logical = max(extent_start, cur_logical);

                /* Truncate the range inside this data stripe */
                extent_size = min(extent_start + extent_size,
                                  logical + map->stripe_len) - cur_logical;
                extent_start = cur_logical;
                ASSERT(extent_size <= U32_MAX);

                scrub_parity_mark_sectors_data(sparity, extent_start, extent_size);

                mapped_length = extent_size;
                ret = btrfs_map_block(fs_info, BTRFS_MAP_READ, extent_start,
                                      &mapped_length, &bioc, 0);
                if (!ret && (!bioc || mapped_length < extent_size))
                        ret = -EIO;
                if (ret) {
                        btrfs_put_bioc(bioc);
                        scrub_parity_mark_sectors_error(sparity, extent_start,
                                                        extent_size);
                        break;
                }
                extent_physical = bioc->stripes[0].physical;
                extent_mirror_num = bioc->mirror_num;
                extent_dev = bioc->stripes[0].dev;
                btrfs_put_bioc(bioc);

                ret = btrfs_lookup_csums_range(csum_root, extent_start,
                                               extent_start + extent_size - 1,
                                               &sctx->csum_list, 1, false);
                if (ret) {
                        scrub_parity_mark_sectors_error(sparity, extent_start,
                                                        extent_size);
                        break;
                }

                ret = scrub_extent_for_parity(sparity, extent_start,
                                              extent_size, extent_physical,
                                              extent_dev, extent_flags,
                                              extent_gen, extent_mirror_num);
                scrub_free_csums(sctx);

                if (ret) {
                        scrub_parity_mark_sectors_error(sparity, extent_start,
                                                        extent_size);
                        break;
                }

                cond_resched();
                cur_logical += extent_size;
        }
        btrfs_release_path(path);
        return ret;
}

static noinline_for_stack int scrub_raid56_parity(struct scrub_ctx *sctx,
                                                  struct map_lookup *map,
                                                  struct btrfs_device *sdev,
                                                  u64 logic_start,
                                                  u64 logic_end)
{
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        struct btrfs_path *path;
        u64 cur_logical;
        int ret;
        struct scrub_parity *sparity;
        int nsectors;

        path = btrfs_alloc_path();
        if (!path) {
                spin_lock(&sctx->stat_lock);
                sctx->stat.malloc_errors++;
                spin_unlock(&sctx->stat_lock);
                return -ENOMEM;
        }
        path->search_commit_root = 1;
        path->skip_locking = 1;

        ASSERT(map->stripe_len <= U32_MAX);
        nsectors = map->stripe_len >> fs_info->sectorsize_bits;
        ASSERT(nsectors <= BITS_PER_LONG);
        sparity = kzalloc(sizeof(struct scrub_parity), GFP_NOFS);
        if (!sparity) {
                spin_lock(&sctx->stat_lock);
                sctx->stat.malloc_errors++;
                spin_unlock(&sctx->stat_lock);
                btrfs_free_path(path);
                return -ENOMEM;
        }

        ASSERT(map->stripe_len <= U32_MAX);
        sparity->stripe_len = map->stripe_len;
        sparity->nsectors = nsectors;
        sparity->sctx = sctx;
        sparity->scrub_dev = sdev;
        sparity->logic_start = logic_start;
        sparity->logic_end = logic_end;
        refcount_set(&sparity->refs, 1);
        INIT_LIST_HEAD(&sparity->sectors_list);

        ret = 0;
        for (cur_logical = logic_start; cur_logical < logic_end;
             cur_logical += map->stripe_len) {
                ret = scrub_raid56_data_stripe_for_parity(sctx, sparity, map,
                                                          sdev, path, cur_logical);
                if (ret < 0)
                        break;
        }

        scrub_parity_put(sparity);
        scrub_submit(sctx);
        mutex_lock(&sctx->wr_lock);
        scrub_wr_submit(sctx);
        mutex_unlock(&sctx->wr_lock);

        btrfs_free_path(path);
        return ret < 0 ? ret : 0;
}

static void sync_replace_for_zoned(struct scrub_ctx *sctx)
{
        if (!btrfs_is_zoned(sctx->fs_info))
                return;

        sctx->flush_all_writes = true;
        scrub_submit(sctx);
        mutex_lock(&sctx->wr_lock);
        scrub_wr_submit(sctx);
        mutex_unlock(&sctx->wr_lock);

        wait_event(sctx->list_wait, atomic_read(&sctx->bios_in_flight) == 0);
}

static int sync_write_pointer_for_zoned(struct scrub_ctx *sctx, u64 logical,
                                        u64 physical, u64 physical_end)
{
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        int ret = 0;

        if (!btrfs_is_zoned(fs_info))
                return 0;

        wait_event(sctx->list_wait, atomic_read(&sctx->bios_in_flight) == 0);

        mutex_lock(&sctx->wr_lock);
        if (sctx->write_pointer < physical_end) {
                ret = btrfs_sync_zone_write_pointer(sctx->wr_tgtdev, logical,
                                                    physical,
                                                    sctx->write_pointer);
                if (ret)
                        btrfs_err(fs_info,
                                  "zoned: failed to recover write pointer");
        }
        mutex_unlock(&sctx->wr_lock);
        btrfs_dev_clear_zone_empty(sctx->wr_tgtdev, physical);

        return ret;
}

/*
 * Scrub one range which can only has simple mirror based profile.
 * (Including all range in SINGLE/DUP/RAID1/RAID1C*, and each stripe in
 *  RAID0/RAID10).
 *
 * Since we may need to handle a subset of block group, we need @logical_start
 * and @logical_length parameter.
 */
static int scrub_simple_mirror(struct scrub_ctx *sctx,
                               struct btrfs_root *extent_root,
                               struct btrfs_root *csum_root,
                               struct btrfs_block_group *bg,
                               struct map_lookup *map,
                               u64 logical_start, u64 logical_length,
                               struct btrfs_device *device,
                               u64 physical, int mirror_num)
{
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        const u64 logical_end = logical_start + logical_length;
        /* An artificial limit, inherit from old scrub behavior */
        const u32 max_length = SZ_64K;
        struct btrfs_path path = { 0 };
        u64 cur_logical = logical_start;
        int ret;

        /* The range must be inside the bg */
        ASSERT(logical_start >= bg->start && logical_end <= bg->start + bg->length);

        path.search_commit_root = 1;
        path.skip_locking = 1;
        /* Go through each extent items inside the logical range */
        while (cur_logical < logical_end) {
                u64 extent_start;
                u64 extent_len;
                u64 extent_flags;
                u64 extent_gen;
                u64 scrub_len;

                /* Canceled? */
                if (atomic_read(&fs_info->scrub_cancel_req) ||
                    atomic_read(&sctx->cancel_req)) {
                        ret = -ECANCELED;
                        break;
                }
                /* Paused? */
                if (atomic_read(&fs_info->scrub_pause_req)) {
                        /* Push queued extents */
                        sctx->flush_all_writes = true;
                        scrub_submit(sctx);
                        mutex_lock(&sctx->wr_lock);
                        scrub_wr_submit(sctx);
                        mutex_unlock(&sctx->wr_lock);
                        wait_event(sctx->list_wait,
                                   atomic_read(&sctx->bios_in_flight) == 0);
                        sctx->flush_all_writes = false;
                        scrub_blocked_if_needed(fs_info);
                }
                /* Block group removed? */
                spin_lock(&bg->lock);
                if (test_bit(BLOCK_GROUP_FLAG_REMOVED, &bg->runtime_flags)) {
                        spin_unlock(&bg->lock);
                        ret = 0;
                        break;
                }
                spin_unlock(&bg->lock);

                ret = find_first_extent_item(extent_root, &path, cur_logical,
                                             logical_end - cur_logical);
                if (ret > 0) {
                        /* No more extent, just update the accounting */
                        sctx->stat.last_physical = physical + logical_length;
                        ret = 0;
                        break;
                }
                if (ret < 0)
                        break;
                get_extent_info(&path, &extent_start, &extent_len,
                                &extent_flags, &extent_gen);
                /* Skip hole range which doesn't have any extent */
                cur_logical = max(extent_start, cur_logical);

                /*
                 * Scrub len has three limits:
                 * - Extent size limit
                 * - Scrub range limit
                 *   This is especially imporatant for RAID0/RAID10 to reuse
                 *   this function
                 * - Max scrub size limit
                 */
                scrub_len = min(min(extent_start + extent_len,
                                    logical_end), cur_logical + max_length) -
                            cur_logical;

                if (extent_flags & BTRFS_EXTENT_FLAG_DATA) {
                        ret = btrfs_lookup_csums_range(csum_root, cur_logical,
                                        cur_logical + scrub_len - 1,
                                        &sctx->csum_list, 1, false);
                        if (ret)
                                break;
                }
                if ((extent_flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) &&
                    does_range_cross_boundary(extent_start, extent_len,
                                              logical_start, logical_length)) {
                        btrfs_err(fs_info,
"scrub: tree block %llu spanning boundaries, ignored. boundary=[%llu, %llu)",
                                  extent_start, logical_start, logical_end);
                        spin_lock(&sctx->stat_lock);
                        sctx->stat.uncorrectable_errors++;
                        spin_unlock(&sctx->stat_lock);
                        cur_logical += scrub_len;
                        continue;
                }
                ret = scrub_extent(sctx, map, cur_logical, scrub_len,
                                   cur_logical - logical_start + physical,
                                   device, extent_flags, extent_gen,
                                   mirror_num);
                scrub_free_csums(sctx);
                if (ret)
                        break;
                if (sctx->is_dev_replace)
                        sync_replace_for_zoned(sctx);
                cur_logical += scrub_len;
                /* Don't hold CPU for too long time */
                cond_resched();
        }
        btrfs_release_path(&path);
        return ret;
}

/* Calculate the full stripe length for simple stripe based profiles */
static u64 simple_stripe_full_stripe_len(const struct map_lookup *map)
{
        ASSERT(map->type & (BTRFS_BLOCK_GROUP_RAID0 |
                            BTRFS_BLOCK_GROUP_RAID10));

        return map->num_stripes / map->sub_stripes * map->stripe_len;
}

/* Get the logical bytenr for the stripe */
static u64 simple_stripe_get_logical(struct map_lookup *map,
                                     struct btrfs_block_group *bg,
                                     int stripe_index)
{
        ASSERT(map->type & (BTRFS_BLOCK_GROUP_RAID0 |
                            BTRFS_BLOCK_GROUP_RAID10));
        ASSERT(stripe_index < map->num_stripes);

        /*
         * (stripe_index / sub_stripes) gives how many data stripes we need to
         * skip.
         */
        return (stripe_index / map->sub_stripes) * map->stripe_len + bg->start;
}

/* Get the mirror number for the stripe */
static int simple_stripe_mirror_num(struct map_lookup *map, int stripe_index)
{
        ASSERT(map->type & (BTRFS_BLOCK_GROUP_RAID0 |
                            BTRFS_BLOCK_GROUP_RAID10));
        ASSERT(stripe_index < map->num_stripes);

        /* For RAID0, it's fixed to 1, for RAID10 it's 0,1,0,1... */
        return stripe_index % map->sub_stripes + 1;
}

static int scrub_simple_stripe(struct scrub_ctx *sctx,
                               struct btrfs_root *extent_root,
                               struct btrfs_root *csum_root,
                               struct btrfs_block_group *bg,
                               struct map_lookup *map,
                               struct btrfs_device *device,
                               int stripe_index)
{
        const u64 logical_increment = simple_stripe_full_stripe_len(map);
        const u64 orig_logical = simple_stripe_get_logical(map, bg, stripe_index);
        const u64 orig_physical = map->stripes[stripe_index].physical;
        const int mirror_num = simple_stripe_mirror_num(map, stripe_index);
        u64 cur_logical = orig_logical;
        u64 cur_physical = orig_physical;
        int ret = 0;

        while (cur_logical < bg->start + bg->length) {
                /*
                 * Inside each stripe, RAID0 is just SINGLE, and RAID10 is
                 * just RAID1, so we can reuse scrub_simple_mirror() to scrub
                 * this stripe.
                 */
                ret = scrub_simple_mirror(sctx, extent_root, csum_root, bg, map,
                                          cur_logical, map->stripe_len, device,
                                          cur_physical, mirror_num);
                if (ret)
                        return ret;
                /* Skip to next stripe which belongs to the target device */
                cur_logical += logical_increment;
                /* For physical offset, we just go to next stripe */
                cur_physical += map->stripe_len;
        }
        return ret;
}

static noinline_for_stack int scrub_stripe(struct scrub_ctx *sctx,
                                           struct btrfs_block_group *bg,
                                           struct extent_map *em,
                                           struct btrfs_device *scrub_dev,
                                           int stripe_index)
{
        struct btrfs_path *path;
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        struct btrfs_root *root;
        struct btrfs_root *csum_root;
        struct blk_plug plug;
        struct map_lookup *map = em->map_lookup;
        const u64 profile = map->type & BTRFS_BLOCK_GROUP_PROFILE_MASK;
        const u64 chunk_logical = bg->start;
        int ret;
        u64 physical = map->stripes[stripe_index].physical;
        const u64 dev_stripe_len = btrfs_calc_stripe_length(em);
        const u64 physical_end = physical + dev_stripe_len;
        u64 logical;
        u64 logic_end;
        /* The logical increment after finishing one stripe */
        u64 increment;
        /* Offset inside the chunk */
        u64 offset;
        u64 stripe_logical;
        u64 stripe_end;
        int stop_loop = 0;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        /*
         * work on commit root. The related disk blocks are static as
         * long as COW is applied. This means, it is save to rewrite
         * them to repair disk errors without any race conditions
         */
        path->search_commit_root = 1;
        path->skip_locking = 1;
        path->reada = READA_FORWARD;

        wait_event(sctx->list_wait,
                   atomic_read(&sctx->bios_in_flight) == 0);
        scrub_blocked_if_needed(fs_info);

        root = btrfs_extent_root(fs_info, bg->start);
        csum_root = btrfs_csum_root(fs_info, bg->start);

        /*
         * collect all data csums for the stripe to avoid seeking during
         * the scrub. This might currently (crc32) end up to be about 1MB
         */
        blk_start_plug(&plug);

        if (sctx->is_dev_replace &&
            btrfs_dev_is_sequential(sctx->wr_tgtdev, physical)) {
                mutex_lock(&sctx->wr_lock);
                sctx->write_pointer = physical;
                mutex_unlock(&sctx->wr_lock);
                sctx->flush_all_writes = true;
        }

        /*
         * There used to be a big double loop to handle all profiles using the
         * same routine, which grows larger and more gross over time.
         *
         * So here we handle each profile differently, so simpler profiles
         * have simpler scrubbing function.
         */
        if (!(profile & (BTRFS_BLOCK_GROUP_RAID0 | BTRFS_BLOCK_GROUP_RAID10 |
                         BTRFS_BLOCK_GROUP_RAID56_MASK))) {
                /*
                 * Above check rules out all complex profile, the remaining
                 * profiles are SINGLE|DUP|RAID1|RAID1C*, which is simple
                 * mirrored duplication without stripe.
                 *
                 * Only @physical and @mirror_num needs to calculated using
                 * @stripe_index.
                 */
                ret = scrub_simple_mirror(sctx, root, csum_root, bg, map,
                                bg->start, bg->length, scrub_dev,
                                map->stripes[stripe_index].physical,
                                stripe_index + 1);
                offset = 0;
                goto out;
        }
        if (profile & (BTRFS_BLOCK_GROUP_RAID0 | BTRFS_BLOCK_GROUP_RAID10)) {
                ret = scrub_simple_stripe(sctx, root, csum_root, bg, map,
                                          scrub_dev, stripe_index);
                offset = map->stripe_len * (stripe_index / map->sub_stripes);
                goto out;
        }

        /* Only RAID56 goes through the old code */
        ASSERT(map->type & BTRFS_BLOCK_GROUP_RAID56_MASK);
        ret = 0;

        /* Calculate the logical end of the stripe */
        get_raid56_logic_offset(physical_end, stripe_index,
                                map, &logic_end, NULL);
        logic_end += chunk_logical;

        /* Initialize @offset in case we need to go to out: label */
        get_raid56_logic_offset(physical, stripe_index, map, &offset, NULL);
        increment = map->stripe_len * nr_data_stripes(map);

        /*
         * Due to the rotation, for RAID56 it's better to iterate each stripe
         * using their physical offset.
         */
        while (physical < physical_end) {
                ret = get_raid56_logic_offset(physical, stripe_index, map,
                                              &logical, &stripe_logical);
                logical += chunk_logical;
                if (ret) {
                        /* it is parity strip */
                        stripe_logical += chunk_logical;
                        stripe_end = stripe_logical + increment;
                        ret = scrub_raid56_parity(sctx, map, scrub_dev,
                                                  stripe_logical,
                                                  stripe_end);
                        if (ret)
                                goto out;
                        goto next;
                }

                /*
                 * Now we're at a data stripe, scrub each extents in the range.
                 *
                 * At this stage, if we ignore the repair part, inside each data
                 * stripe it is no different than SINGLE profile.
                 * We can reuse scrub_simple_mirror() here, as the repair part
                 * is still based on @mirror_num.
                 */
                ret = scrub_simple_mirror(sctx, root, csum_root, bg, map,
                                          logical, map->stripe_len,
                                          scrub_dev, physical, 1);
                if (ret < 0)
                        goto out;
next:
                logical += increment;
                physical += map->stripe_len;
                spin_lock(&sctx->stat_lock);
                if (stop_loop)
                        sctx->stat.last_physical =
                                map->stripes[stripe_index].physical + dev_stripe_len;
                else
                        sctx->stat.last_physical = physical;
                spin_unlock(&sctx->stat_lock);
                if (stop_loop)
                        break;
        }
out:
        /* push queued extents */
        scrub_submit(sctx);
        mutex_lock(&sctx->wr_lock);
        scrub_wr_submit(sctx);
        mutex_unlock(&sctx->wr_lock);

        blk_finish_plug(&plug);
        btrfs_free_path(path);

        if (sctx->is_dev_replace && ret >= 0) {
                int ret2;

                ret2 = sync_write_pointer_for_zoned(sctx,
                                chunk_logical + offset,
                                map->stripes[stripe_index].physical,
                                physical_end);
                if (ret2)
                        ret = ret2;
        }

        return ret < 0 ? ret : 0;
}

static noinline_for_stack int scrub_chunk(struct scrub_ctx *sctx,
                                          struct btrfs_block_group *bg,
                                          struct btrfs_device *scrub_dev,
                                          u64 dev_offset,
                                          u64 dev_extent_len)
{
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        struct extent_map_tree *map_tree = &fs_info->mapping_tree;
        struct map_lookup *map;
        struct extent_map *em;
        int i;
        int ret = 0;

        read_lock(&map_tree->lock);
        em = lookup_extent_mapping(map_tree, bg->start, bg->length);
        read_unlock(&map_tree->lock);

        if (!em) {
                /*
                 * Might have been an unused block group deleted by the cleaner
                 * kthread or relocation.
                 */
                spin_lock(&bg->lock);
                if (!test_bit(BLOCK_GROUP_FLAG_REMOVED, &bg->runtime_flags))
                        ret = -EINVAL;
                spin_unlock(&bg->lock);

                return ret;
        }
        if (em->start != bg->start)
                goto out;
        if (em->len < dev_extent_len)
                goto out;

        map = em->map_lookup;
        for (i = 0; i < map->num_stripes; ++i) {
                if (map->stripes[i].dev->bdev == scrub_dev->bdev &&
                    map->stripes[i].physical == dev_offset) {
                        ret = scrub_stripe(sctx, bg, em, scrub_dev, i);
                        if (ret)
                                goto out;
                }
        }
out:
        free_extent_map(em);

        return ret;
}

static int finish_extent_writes_for_zoned(struct btrfs_root *root,
                                          struct btrfs_block_group *cache)
{
        struct btrfs_fs_info *fs_info = cache->fs_info;
        struct btrfs_trans_handle *trans;

        if (!btrfs_is_zoned(fs_info))
                return 0;

        btrfs_wait_block_group_reservations(cache);
        btrfs_wait_nocow_writers(cache);
        btrfs_wait_ordered_roots(fs_info, U64_MAX, cache->start, cache->length);

        trans = btrfs_join_transaction(root);
        if (IS_ERR(trans))
                return PTR_ERR(trans);
        return btrfs_commit_transaction(trans);
}

static noinline_for_stack
int scrub_enumerate_chunks(struct scrub_ctx *sctx,
                           struct btrfs_device *scrub_dev, u64 start, u64 end)
{
        struct btrfs_dev_extent *dev_extent = NULL;
        struct btrfs_path *path;
        struct btrfs_fs_info *fs_info = sctx->fs_info;
        struct btrfs_root *root = fs_info->dev_root;
        u64 chunk_offset;
        int ret = 0;
        int ro_set;
        int slot;
        struct extent_buffer *l;
        struct btrfs_key key;
        struct btrfs_key found_key;
        struct btrfs_block_group *cache;
        struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        path->reada = READA_FORWARD;
        path->search_commit_root = 1;
        path->skip_locking = 1;

        key.objectid = scrub_dev->devid;
        key.offset = 0ull;
        key.type = BTRFS_DEV_EXTENT_KEY;

        while (1) {
                u64 dev_extent_len;

                ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
                if (ret < 0)
                        break;
                if (ret > 0) {
                        if (path->slots[0] >=
                            btrfs_header_nritems(path->nodes[0])) {
                                ret = btrfs_next_leaf(root, path);
                                if (ret < 0)
                                        break;
                                if (ret > 0) {
                                        ret = 0;
                                        break;
                                }
                        } else {
                                ret = 0;
                        }
                }

                l = path->nodes[0];
                slot = path->slots[0];

                btrfs_item_key_to_cpu(l, &found_key, slot);

                if (found_key.objectid != scrub_dev->devid)
                        break;

                if (found_key.type != BTRFS_DEV_EXTENT_KEY)
                        break;

                if (found_key.offset >= end)
                        break;

                if (found_key.offset < key.offset)
                        break;

                dev_extent = btrfs_item_ptr(l, slot, struct btrfs_dev_extent);
                dev_extent_len = btrfs_dev_extent_length(l, dev_extent);

                if (found_key.offset + dev_extent_len <= start)
                        goto skip;

                chunk_offset = btrfs_dev_extent_chunk_offset(l, dev_extent);

                /*
                 * get a reference on the corresponding block group to prevent
                 * the chunk from going away while we scrub it
                 */
                cache = btrfs_lookup_block_group(fs_info, chunk_offset);

                /* some chunks are removed but not committed to disk yet,
                 * continue scrubbing */
                if (!cache)
                        goto skip;

                ASSERT(cache->start <= chunk_offset);
                /*
                 * We are using the commit root to search for device extents, so
                 * that means we could have found a device extent item from a
                 * block group that was deleted in the current transaction. The
                 * logical start offset of the deleted block group, stored at
                 * @chunk_offset, might be part of the logical address range of
                 * a new block group (which uses different physical extents).
                 * In this case btrfs_lookup_block_group() has returned the new
                 * block group, and its start address is less than @chunk_offset.
                 *
                 * We skip such new block groups, because it's pointless to
                 * process them, as we won't find their extents because we search
                 * for them using the commit root of the extent tree. For a device
                 * replace it's also fine to skip it, we won't miss copying them
                 * to the target device because we have the write duplication
                 * setup through the regular write path (by btrfs_map_block()),
                 * and we have committed a transaction when we started the device
                 * replace, right after setting up the device replace state.
                 */
                if (cache->start < chunk_offset) {
                        btrfs_put_block_group(cache);
                        goto skip;
                }

                if (sctx->is_dev_replace && btrfs_is_zoned(fs_info)) {
                        if (!test_bit(BLOCK_GROUP_FLAG_TO_COPY, &cache->runtime_flags)) {
                                btrfs_put_block_group(cache);
                                goto skip;
                        }
                }

                /*
                 * Make sure that while we are scrubbing the corresponding block
                 * group doesn't get its logical address and its device extents
                 * reused for another block group, which can possibly be of a
                 * different type and different profile. We do this to prevent
                 * false error detections and crashes due to bogus attempts to
                 * repair extents.
                 */
                spin_lock(&cache->lock);
                if (test_bit(BLOCK_GROUP_FLAG_REMOVED, &cache->runtime_flags)) {
                        spin_unlock(&cache->lock);
                        btrfs_put_block_group(cache);
                        goto skip;
                }
                btrfs_freeze_block_group(cache);
                spin_unlock(&cache->lock);

                /*
                 * we need call btrfs_inc_block_group_ro() with scrubs_paused,
                 * to avoid deadlock caused by:
                 * btrfs_inc_block_group_ro()
                 * -> btrfs_wait_for_commit()
                 * -> btrfs_commit_transaction()
                 * -> btrfs_scrub_pause()
                 */
                scrub_pause_on(fs_info);

                /*
                 * Don't do chunk preallocation for scrub.
                 *
                 * This is especially important for SYSTEM bgs, or we can hit
                 * -EFBIG from btrfs_finish_chunk_alloc() like:
                 * 1. The only SYSTEM bg is marked RO.
                 *    Since SYSTEM bg is small, that's pretty common.
                 * 2. New SYSTEM bg will be allocated
                 *    Due to regular version will allocate new chunk.
                 * 3. New SYSTEM bg is empty and will get cleaned up
                 *    Before cleanup really happens, it's marked RO again.
                 * 4. Empty SYSTEM bg get scrubbed
                 *    We go back to 2.
                 *
                 * This can easily boost the amount of SYSTEM chunks if cleaner
                 * thread can't be triggered fast enough, and use up all space
                 * of btrfs_super_block::sys_chunk_array
                 *
                 * While for dev replace, we need to try our best to mark block
                 * group RO, to prevent race between:
                 * - Write duplication
                 *   Contains latest data
                 * - Scrub copy
                 *   Contains data from commit tree
                 *
                 * If target block group is not marked RO, nocow writes can
                 * be overwritten by scrub copy, causing data corruption.
                 * So for dev-replace, it's not allowed to continue if a block
                 * group is not RO.
                 */
                ret = btrfs_inc_block_group_ro(cache, sctx->is_dev_replace);
                if (!ret && sctx->is_dev_replace) {
                        ret = finish_extent_writes_for_zoned(root, cache);
                        if (ret) {
                                btrfs_dec_block_group_ro(cache);
                                scrub_pause_off(fs_info);
                                btrfs_put_block_group(cache);
                                break;
                        }
                }

                if (ret == 0) {
                        ro_set = 1;
                } else if (ret == -ENOSPC && !sctx->is_dev_replace &&
                           !(cache->flags & BTRFS_BLOCK_GROUP_RAID56_MASK)) {
                        /*
                         * btrfs_inc_block_group_ro return -ENOSPC when it
                         * failed in creating new chunk for metadata.
                         * It is not a problem for scrub, because
                         * metadata are always cowed, and our scrub paused
                         * commit_transactions.
                         *
                         * For RAID56 chunks, we have to mark them read-only
                         * for scrub, as later we would use our own cache
                         * out of RAID56 realm.
                         * Thus we want the RAID56 bg to be marked RO to
                         * prevent RMW from screwing up out cache.
                         */
                        ro_set = 0;
                } else if (ret == -ETXTBSY) {
                        btrfs_warn(fs_info,
                   "skipping scrub of block group %llu due to active swapfile",
                                   cache->start);
                        scrub_pause_off(fs_info);
                        ret = 0;
                        goto skip_unfreeze;
                } else {
                        btrfs_warn(fs_info,
                                   "failed setting block group ro: %d", ret);
                        btrfs_unfreeze_block_group(cache);
                        btrfs_put_block_group(cache);
                        scrub_pause_off(fs_info);
                        break;
                }

                /*
                 * Now the target block is marked RO, wait for nocow writes to
                 * finish before dev-replace.
                 * COW is fine, as COW never overwrites extents in commit tree.
                 */
                if (sctx->is_dev_replace) {
                        btrfs_wait_nocow_writers(cache);
                        btrfs_wait_ordered_roots(fs_info, U64_MAX, cache->start,
                                        cache->length);
                }

                scrub_pause_off(fs_info);
                down_write(&dev_replace->rwsem);
                dev_replace->cursor_right = found_key.offset + dev_extent_len;
                dev_replace->cursor_left = found_key.offset;
                dev_replace->item_needs_writeback = 1;
                up_write(&dev_replace->rwsem);

                ret = scrub_chunk(sctx, cache, scrub_dev, found_key.offset,
                                  dev_extent_len);

                /*
                 * flush, submit all pending read and write bios, afterwards
                 * wait for them.
                 * Note that in the dev replace case, a read request causes
                 * write requests that are submitted in the read completion
                 * worker. Therefore in the current situation, it is required
                 * that all write requests are flushed, so that all read and
                 * write requests are really completed when bios_in_flight
                 * changes to 0.
                 */
                sctx->flush_all_writes = true;
                scrub_submit(sctx);
                mutex_lock(&sctx->wr_lock);
                scrub_wr_submit(sctx);
                mutex_unlock(&sctx->wr_lock);

                wait_event(sctx->list_wait,
                           atomic_read(&sctx->bios_in_flight) == 0);

                scrub_pause_on(fs_info);

                /*
                 * must be called before we decrease @scrub_paused.
                 * make sure we don't block transaction commit while
                 * we are waiting pending workers finished.
                 */
                wait_event(sctx->list_wait,
                           atomic_read(&sctx->workers_pending) == 0);
                sctx->flush_all_writes = false;

                scrub_pause_off(fs_info);

                if (sctx->is_dev_replace &&
                    !btrfs_finish_block_group_to_copy(dev_replace->srcdev,
                                                      cache, found_key.offset))
                        ro_set = 0;

                down_write(&dev_replace->rwsem);
                dev_replace->cursor_left = dev_replace->cursor_right;
                dev_replace->item_needs_writeback = 1;
                up_write(&dev_replace->rwsem);

                if (ro_set)
                        btrfs_dec_block_group_ro(cache);

                /*
                 * We might have prevented the cleaner kthread from deleting
                 * this block group if it was already unused because we raced
                 * and set it to RO mode first. So add it back to the unused
                 * list, otherwise it might not ever be deleted unless a manual
                 * balance is triggered or it becomes used and unused again.
                 */
                spin_lock(&cache->lock);
                if (!test_bit(BLOCK_GROUP_FLAG_REMOVED, &cache->runtime_flags) &&
                    !cache->ro && cache->reserved == 0 && cache->used == 0) {
                        spin_unlock(&cache->lock);
                        if (btrfs_test_opt(fs_info, DISCARD_ASYNC))
                                btrfs_discard_queue_work(&fs_info->discard_ctl,
                                                         cache);
                        else
                                btrfs_mark_bg_unused(cache);
                } else {
                        spin_unlock(&cache->lock);
                }
skip_unfreeze:
                btrfs_unfreeze_block_group(cache);
                btrfs_put_block_group(cache);
                if (ret)
                        break;
                if (sctx->is_dev_replace &&
                    atomic64_read(&dev_replace->num_write_errors) > 0) {
                        ret = -EIO;
                        break;
                }
                if (sctx->stat.malloc_errors > 0) {
                        ret = -ENOMEM;
                        break;
                }
skip:
                key.offset = found_key.offset + dev_extent_len;
                btrfs_release_path(path);
        }

        btrfs_free_path(path);

        return ret;
}

static noinline_for_stack int scrub_supers(struct scrub_ctx *sctx,
                                           struct btrfs_device *scrub_dev)
{
        int     i;
        u64     bytenr;
        u64     gen;
        int     ret;
        struct btrfs_fs_info *fs_info = sctx->fs_info;

        if (BTRFS_FS_ERROR(fs_info))
                return -EROFS;

        /* Seed devices of a new filesystem has their own generation. */
        if (scrub_dev->fs_devices != fs_info->fs_devices)
                gen = scrub_dev->generation;
        else
                gen = fs_info->last_trans_committed;

        for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
                ret = btrfs_sb_log_location(scrub_dev, i, 0, &bytenr);
                if (ret == -ENOENT)
                        break;

                if (ret) {
                        spin_lock(&sctx->stat_lock);
                        sctx->stat.super_errors++;
                        spin_unlock(&sctx->stat_lock);
                        continue;
                }

                if (bytenr + BTRFS_SUPER_INFO_SIZE >
                    scrub_dev->commit_total_bytes)
                        break;
                if (!btrfs_check_super_location(scrub_dev, bytenr))
                        continue;

                ret = scrub_sectors(sctx, bytenr, BTRFS_SUPER_INFO_SIZE, bytenr,
                                    scrub_dev, BTRFS_EXTENT_FLAG_SUPER, gen, i,
                                    NULL, bytenr);
                if (ret)
                        return ret;
        }
        wait_event(sctx->list_wait, atomic_read(&sctx->bios_in_flight) == 0);

        return 0;
}

static void scrub_workers_put(struct btrfs_fs_info *fs_info)
{
        if (refcount_dec_and_mutex_lock(&fs_info->scrub_workers_refcnt,
                                        &fs_info->scrub_lock)) {
                struct workqueue_struct *scrub_workers = fs_info->scrub_workers;
                struct workqueue_struct *scrub_wr_comp =
                                                fs_info->scrub_wr_completion_workers;
                struct workqueue_struct *scrub_parity =
                                                fs_info->scrub_parity_workers;

                fs_info->scrub_workers = NULL;
                fs_info->scrub_wr_completion_workers = NULL;
                fs_info->scrub_parity_workers = NULL;
                mutex_unlock(&fs_info->scrub_lock);

                if (scrub_workers)
                        destroy_workqueue(scrub_workers);
                if (scrub_wr_comp)
                        destroy_workqueue(scrub_wr_comp);
                if (scrub_parity)
                        destroy_workqueue(scrub_parity);
        }
}

/*
 * get a reference count on fs_info->scrub_workers. start worker if necessary
 */
static noinline_for_stack int scrub_workers_get(struct btrfs_fs_info *fs_info,
                                                int is_dev_replace)
{
        struct workqueue_struct *scrub_workers = NULL;
        struct workqueue_struct *scrub_wr_comp = NULL;
        struct workqueue_struct *scrub_parity = NULL;
        unsigned int flags = WQ_FREEZABLE | WQ_UNBOUND;
        int max_active = fs_info->thread_pool_size;
        int ret = -ENOMEM;

        if (refcount_inc_not_zero(&fs_info->scrub_workers_refcnt))
                return 0;

        scrub_workers = alloc_workqueue("btrfs-scrub", flags,
                                        is_dev_replace ? 1 : max_active);
        if (!scrub_workers)
                goto fail_scrub_workers;

        scrub_wr_comp = alloc_workqueue("btrfs-scrubwrc", flags, max_active);
        if (!scrub_wr_comp)
                goto fail_scrub_wr_completion_workers;

        scrub_parity = alloc_workqueue("btrfs-scrubparity", flags, max_active);
        if (!scrub_parity)
                goto fail_scrub_parity_workers;

        mutex_lock(&fs_info->scrub_lock);
        if (refcount_read(&fs_info->scrub_workers_refcnt) == 0) {
                ASSERT(fs_info->scrub_workers == NULL &&
                       fs_info->scrub_wr_completion_workers == NULL &&
                       fs_info->scrub_parity_workers == NULL);
                fs_info->scrub_workers = scrub_workers;
                fs_info->scrub_wr_completion_workers = scrub_wr_comp;
                fs_info->scrub_parity_workers = scrub_parity;
                refcount_set(&fs_info->scrub_workers_refcnt, 1);
                mutex_unlock(&fs_info->scrub_lock);
                return 0;
        }
        /* Other thread raced in and created the workers for us */
        refcount_inc(&fs_info->scrub_workers_refcnt);
        mutex_unlock(&fs_info->scrub_lock);

        ret = 0;
        destroy_workqueue(scrub_parity);
fail_scrub_parity_workers:
        destroy_workqueue(scrub_wr_comp);
fail_scrub_wr_completion_workers:
        destroy_workqueue(scrub_workers);
fail_scrub_workers:
        return ret;
}

int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
                    u64 end, struct btrfs_scrub_progress *progress,
                    int readonly, int is_dev_replace)
{
        struct btrfs_dev_lookup_args args = { .devid = devid };
        struct scrub_ctx *sctx;
        int ret;
        struct btrfs_device *dev;
        unsigned int nofs_flag;
        bool need_commit = false;

        if (btrfs_fs_closing(fs_info))
                return -EAGAIN;

        /* At mount time we have ensured nodesize is in the range of [4K, 64K]. */
        ASSERT(fs_info->nodesize <= BTRFS_STRIPE_LEN);

        /*
         * SCRUB_MAX_SECTORS_PER_BLOCK is calculated using the largest possible
         * value (max nodesize / min sectorsize), thus nodesize should always
         * be fine.
         */
        ASSERT(fs_info->nodesize <=
               SCRUB_MAX_SECTORS_PER_BLOCK << fs_info->sectorsize_bits);

        /* Allocate outside of device_list_mutex */
        sctx = scrub_setup_ctx(fs_info, is_dev_replace);
        if (IS_ERR(sctx))
                return PTR_ERR(sctx);

        ret = scrub_workers_get(fs_info, is_dev_replace);
        if (ret)
                goto out_free_ctx;

        mutex_lock(&fs_info->fs_devices->device_list_mutex);
        dev = btrfs_find_device(fs_info->fs_devices, &args);
        if (!dev || (test_bit(BTRFS_DEV_STATE_MISSING, &dev->dev_state) &&
                     !is_dev_replace)) {
                mutex_unlock(&fs_info->fs_devices->device_list_mutex);
                ret = -ENODEV;
                goto out;
        }

        if (!is_dev_replace && !readonly &&
            !test_bit(BTRFS_DEV_STATE_WRITEABLE, &dev->dev_state)) {
                mutex_unlock(&fs_info->fs_devices->device_list_mutex);
                btrfs_err_in_rcu(fs_info,
                        "scrub on devid %llu: filesystem on %s is not writable",
                                 devid, rcu_str_deref(dev->name));
                ret = -EROFS;
                goto out;
        }

        mutex_lock(&fs_info->scrub_lock);
        if (!test_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &dev->dev_state) ||
            test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &dev->dev_state)) {
                mutex_unlock(&fs_info->scrub_lock);
                mutex_unlock(&fs_info->fs_devices->device_list_mutex);
                ret = -EIO;
                goto out;
        }

        down_read(&fs_info->dev_replace.rwsem);
        if (dev->scrub_ctx ||
            (!is_dev_replace &&
             btrfs_dev_replace_is_ongoing(&fs_info->dev_replace))) {
                up_read(&fs_info->dev_replace.rwsem);
                mutex_unlock(&fs_info->scrub_lock);
                mutex_unlock(&fs_info->fs_devices->device_list_mutex);
                ret = -EINPROGRESS;
                goto out;
        }
        up_read(&fs_info->dev_replace.rwsem);

        sctx->readonly = readonly;
        dev->scrub_ctx = sctx;
        mutex_unlock(&fs_info->fs_devices->device_list_mutex);

        /*
         * checking @scrub_pause_req here, we can avoid
         * race between committing transaction and scrubbing.
         */
        __scrub_blocked_if_needed(fs_info);
        atomic_inc(&fs_info->scrubs_running);
        mutex_unlock(&fs_info->scrub_lock);

        /*
         * In order to avoid deadlock with reclaim when there is a transaction
         * trying to pause scrub, make sure we use GFP_NOFS for all the
         * allocations done at btrfs_scrub_sectors() and scrub_sectors_for_parity()
         * invoked by our callees. The pausing request is done when the
         * transaction commit starts, and it blocks the transaction until scrub
         * is paused (done at specific points at scrub_stripe() or right above
         * before incrementing fs_info->scrubs_running).
         */
        nofs_flag = memalloc_nofs_save();
        if (!is_dev_replace) {
                u64 old_super_errors;

                spin_lock(&sctx->stat_lock);
                old_super_errors = sctx->stat.super_errors;
                spin_unlock(&sctx->stat_lock);

                btrfs_info(fs_info, "scrub: started on devid %llu", devid);
                /*
                 * by holding device list mutex, we can
                 * kick off writing super in log tree sync.
                 */
                mutex_lock(&fs_info->fs_devices->device_list_mutex);
                ret = scrub_supers(sctx, dev);
                mutex_unlock(&fs_info->fs_devices->device_list_mutex);

                spin_lock(&sctx->stat_lock);
                /*
                 * Super block errors found, but we can not commit transaction
                 * at current context, since btrfs_commit_transaction() needs
                 * to pause the current running scrub (hold by ourselves).
                 */
                if (sctx->stat.super_errors > old_super_errors && !sctx->readonly)
                        need_commit = true;
                spin_unlock(&sctx->stat_lock);
        }

        if (!ret)
                ret = scrub_enumerate_chunks(sctx, dev, start, end);
        memalloc_nofs_restore(nofs_flag);

        wait_event(sctx->list_wait, atomic_read(&sctx->bios_in_flight) == 0);
        atomic_dec(&fs_info->scrubs_running);
        wake_up(&fs_info->scrub_pause_wait);

        wait_event(sctx->list_wait, atomic_read(&sctx->workers_pending) == 0);

        if (progress)
                memcpy(progress, &sctx->stat, sizeof(*progress));

        if (!is_dev_replace)
                btrfs_info(fs_info, "scrub: %s on devid %llu with status: %d",
                        ret ? "not finished" : "finished", devid, ret);

        mutex_lock(&fs_info->scrub_lock);
        dev->scrub_ctx = NULL;
        mutex_unlock(&fs_info->scrub_lock);

        scrub_workers_put(fs_info);
        scrub_put_ctx(sctx);

        /*
         * We found some super block errors before, now try to force a
         * transaction commit, as scrub has finished.
         */
        if (need_commit) {
                struct btrfs_trans_handle *trans;

                trans = btrfs_start_transaction(fs_info->tree_root, 0);
                if (IS_ERR(trans)) {
                        ret = PTR_ERR(trans);
                        btrfs_err(fs_info,
        "scrub: failed to start transaction to fix super block errors: %d", ret);
                        return ret;
                }
                ret = btrfs_commit_transaction(trans);
                if (ret < 0)
                        btrfs_err(fs_info,
        "scrub: failed to commit transaction to fix super block errors: %d", ret);
        }
        return ret;
out:
        scrub_workers_put(fs_info);
out_free_ctx:
        scrub_free_ctx(sctx);

        return ret;
}

void btrfs_scrub_pause(struct btrfs_fs_info *fs_info)
{
        mutex_lock(&fs_info->scrub_lock);
        atomic_inc(&fs_info->scrub_pause_req);
        while (atomic_read(&fs_info->scrubs_paused) !=
               atomic_read(&fs_info->scrubs_running)) {
                mutex_unlock(&fs_info->scrub_lock);
                wait_event(fs_info->scrub_pause_wait,
                           atomic_read(&fs_info->scrubs_paused) ==
                           atomic_read(&fs_info->scrubs_running));
                mutex_lock(&fs_info->scrub_lock);
        }
        mutex_unlock(&fs_info->scrub_lock);
}

void btrfs_scrub_continue(struct btrfs_fs_info *fs_info)
{
        atomic_dec(&fs_info->scrub_pause_req);
        wake_up(&fs_info->scrub_pause_wait);
}

int btrfs_scrub_cancel(struct btrfs_fs_info *fs_info)
{
        mutex_lock(&fs_info->scrub_lock);
        if (!atomic_read(&fs_info->scrubs_running)) {
                mutex_unlock(&fs_info->scrub_lock);
                return -ENOTCONN;
        }

        atomic_inc(&fs_info->scrub_cancel_req);
        while (atomic_read(&fs_info->scrubs_running)) {
                mutex_unlock(&fs_info->scrub_lock);
                wait_event(fs_info->scrub_pause_wait,
                           atomic_read(&fs_info->scrubs_running) == 0);
                mutex_lock(&fs_info->scrub_lock);
        }
        atomic_dec(&fs_info->scrub_cancel_req);
        mutex_unlock(&fs_info->scrub_lock);

        return 0;
}

int btrfs_scrub_cancel_dev(struct btrfs_device *dev)
{
        struct btrfs_fs_info *fs_info = dev->fs_info;
        struct scrub_ctx *sctx;

        mutex_lock(&fs_info->scrub_lock);
        sctx = dev->scrub_ctx;
        if (!sctx) {
                mutex_unlock(&fs_info->scrub_lock);
                return -ENOTCONN;
        }
        atomic_inc(&sctx->cancel_req);
        while (dev->scrub_ctx) {
                mutex_unlock(&fs_info->scrub_lock);
                wait_event(fs_info->scrub_pause_wait,
                           dev->scrub_ctx == NULL);
                mutex_lock(&fs_info->scrub_lock);
        }
        mutex_unlock(&fs_info->scrub_lock);

        return 0;
}

int btrfs_scrub_progress(struct btrfs_fs_info *fs_info, u64 devid,
                         struct btrfs_scrub_progress *progress)
{
        struct btrfs_dev_lookup_args args = { .devid = devid };
        struct btrfs_device *dev;
        struct scrub_ctx *sctx = NULL;

        mutex_lock(&fs_info->fs_devices->device_list_mutex);
        dev = btrfs_find_device(fs_info->fs_devices, &args);
        if (dev)
                sctx = dev->scrub_ctx;
        if (sctx)
                memcpy(progress, &sctx->stat, sizeof(*progress));
        mutex_unlock(&fs_info->fs_devices->device_list_mutex);

        return dev ? (sctx ? 0 : -ENOTCONN) : -ENODEV;
}

static void scrub_find_good_copy(struct btrfs_fs_info *fs_info,
                                 u64 extent_logical, u32 extent_len,
                                 u64 *extent_physical,
                                 struct btrfs_device **extent_dev,
                                 int *extent_mirror_num)
{
        u64 mapped_length;
        struct btrfs_io_context *bioc = NULL;
        int ret;

        mapped_length = extent_len;
        ret = btrfs_map_block(fs_info, BTRFS_MAP_READ, extent_logical,
                              &mapped_length, &bioc, 0);
        if (ret || !bioc || mapped_length < extent_len ||
            !bioc->stripes[0].dev->bdev) {
                btrfs_put_bioc(bioc);
                return;
        }

        *extent_physical = bioc->stripes[0].physical;
        *extent_mirror_num = bioc->mirror_num;
        *extent_dev = bioc->stripes[0].dev;
        btrfs_put_bioc(bioc);
}