2 * Functions to sequence PREFLUSH and FUA writes.
4 * Copyright (C) 2011 Max Planck Institute for Gravitational Physics
5 * Copyright (C) 2011 Tejun Heo <tj@kernel.org>
7 * This file is released under the GPLv2.
9 * REQ_{PREFLUSH|FUA} requests are decomposed to sequences consisted of three
10 * optional steps - PREFLUSH, DATA and POSTFLUSH - according to the request
11 * properties and hardware capability.
13 * If a request doesn't have data, only REQ_PREFLUSH makes sense, which
14 * indicates a simple flush request. If there is data, REQ_PREFLUSH indicates
15 * that the device cache should be flushed before the data is executed, and
16 * REQ_FUA means that the data must be on non-volatile media on request
19 * If the device doesn't have writeback cache, PREFLUSH and FUA don't make any
20 * difference. The requests are either completed immediately if there's no data
21 * or executed as normal requests otherwise.
23 * If the device has writeback cache and supports FUA, REQ_PREFLUSH is
24 * translated to PREFLUSH but REQ_FUA is passed down directly with DATA.
26 * If the device has writeback cache and doesn't support FUA, REQ_PREFLUSH
27 * is translated to PREFLUSH and REQ_FUA to POSTFLUSH.
29 * The actual execution of flush is double buffered. Whenever a request
30 * needs to execute PRE or POSTFLUSH, it queues at
31 * fq->flush_queue[fq->flush_pending_idx]. Once certain criteria are met, a
32 * REQ_OP_FLUSH is issued and the pending_idx is toggled. When the flush
33 * completes, all the requests which were pending are proceeded to the next
34 * step. This allows arbitrary merging of different types of PREFLUSH/FUA
37 * Currently, the following conditions are used to determine when to issue
40 * C1. At any given time, only one flush shall be in progress. This makes
41 * double buffering sufficient.
43 * C2. Flush is deferred if any request is executing DATA of its sequence.
44 * This avoids issuing separate POSTFLUSHes for requests which shared
47 * C3. The second condition is ignored if there is a request which has
48 * waited longer than FLUSH_PENDING_TIMEOUT. This is to avoid
49 * starvation in the unlikely case where there are continuous stream of
50 * FUA (without PREFLUSH) requests.
52 * For devices which support FUA, it isn't clear whether C2 (and thus C3)
55 * Note that a sequenced PREFLUSH/FUA request with DATA is completed twice.
56 * Once while executing DATA and again after the whole sequence is
57 * complete. The first completion updates the contained bio but doesn't
58 * finish it so that the bio submitter is notified only after the whole
59 * sequence is complete. This is implemented by testing RQF_FLUSH_SEQ in
62 * The above peculiarity requires that each PREFLUSH/FUA request has only one
63 * bio attached to it, which is guaranteed as they aren't allowed to be
64 * merged in the usual way.
67 #include <linux/kernel.h>
68 #include <linux/module.h>
69 #include <linux/bio.h>
70 #include <linux/blkdev.h>
71 #include <linux/gfp.h>
72 #include <linux/blk-mq.h>
76 #include "blk-mq-tag.h"
77 #include "blk-mq-sched.h"
79 /* PREFLUSH/FUA sequences */
81 REQ_FSEQ_PREFLUSH = (1 << 0), /* pre-flushing in progress */
82 REQ_FSEQ_DATA = (1 << 1), /* data write in progress */
83 REQ_FSEQ_POSTFLUSH = (1 << 2), /* post-flushing in progress */
84 REQ_FSEQ_DONE = (1 << 3),
86 REQ_FSEQ_ACTIONS = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
90 * If flush has been pending longer than the following timeout,
91 * it's issued even if flush_data requests are still in flight.
93 FLUSH_PENDING_TIMEOUT = 5 * HZ,
96 static bool blk_kick_flush(struct request_queue *q,
97 struct blk_flush_queue *fq, unsigned int flags);
99 static unsigned int blk_flush_policy(unsigned long fflags, struct request *rq)
101 unsigned int policy = 0;
103 if (blk_rq_sectors(rq))
104 policy |= REQ_FSEQ_DATA;
106 if (fflags & (1UL << QUEUE_FLAG_WC)) {
107 if (rq->cmd_flags & REQ_PREFLUSH)
108 policy |= REQ_FSEQ_PREFLUSH;
109 if (!(fflags & (1UL << QUEUE_FLAG_FUA)) &&
110 (rq->cmd_flags & REQ_FUA))
111 policy |= REQ_FSEQ_POSTFLUSH;
116 static unsigned int blk_flush_cur_seq(struct request *rq)
118 return 1 << ffz(rq->flush.seq);
121 static void blk_flush_restore_request(struct request *rq)
124 * After flush data completion, @rq->bio is %NULL but we need to
125 * complete the bio again. @rq->biotail is guaranteed to equal the
126 * original @rq->bio. Restore it.
128 rq->bio = rq->biotail;
130 /* make @rq a normal request */
131 rq->rq_flags &= ~RQF_FLUSH_SEQ;
132 rq->end_io = rq->flush.saved_end_io;
135 static bool blk_flush_queue_rq(struct request *rq, bool add_front)
138 blk_mq_add_to_requeue_list(rq, add_front, true);
142 list_add(&rq->queuelist, &rq->q->queue_head);
144 list_add_tail(&rq->queuelist, &rq->q->queue_head);
150 * blk_flush_complete_seq - complete flush sequence
151 * @rq: PREFLUSH/FUA request being sequenced
153 * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
154 * @error: whether an error occurred
156 * @rq just completed @seq part of its flush sequence, record the
157 * completion and trigger the next step.
160 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
163 * %true if requests were added to the dispatch queue, %false otherwise.
165 static bool blk_flush_complete_seq(struct request *rq,
166 struct blk_flush_queue *fq,
167 unsigned int seq, blk_status_t error)
169 struct request_queue *q = rq->q;
170 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
171 bool queued = false, kicked;
172 unsigned int cmd_flags;
174 BUG_ON(rq->flush.seq & seq);
175 rq->flush.seq |= seq;
176 cmd_flags = rq->cmd_flags;
179 seq = blk_flush_cur_seq(rq);
184 case REQ_FSEQ_PREFLUSH:
185 case REQ_FSEQ_POSTFLUSH:
186 /* queue for flush */
187 if (list_empty(pending))
188 fq->flush_pending_since = jiffies;
189 list_move_tail(&rq->flush.list, pending);
193 list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
194 queued = blk_flush_queue_rq(rq, true);
199 * @rq was previously adjusted by blk_flush_issue() for
200 * flush sequencing and may already have gone through the
201 * flush data request completion path. Restore @rq for
202 * normal completion and end it.
204 BUG_ON(!list_empty(&rq->queuelist));
205 list_del_init(&rq->flush.list);
206 blk_flush_restore_request(rq);
208 blk_mq_end_request(rq, error);
210 __blk_end_request_all(rq, error);
217 kicked = blk_kick_flush(q, fq, cmd_flags);
218 return kicked | queued;
221 static void flush_end_io(struct request *flush_rq, blk_status_t error)
223 struct request_queue *q = flush_rq->q;
224 struct list_head *running;
226 struct request *rq, *n;
227 unsigned long flags = 0;
228 struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
231 struct blk_mq_hw_ctx *hctx;
233 /* release the tag's ownership to the req cloned from */
234 spin_lock_irqsave(&fq->mq_flush_lock, flags);
236 if (!refcount_dec_and_test(&flush_rq->ref)) {
237 fq->rq_status = error;
238 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
242 if (fq->rq_status != BLK_STS_OK)
243 error = fq->rq_status;
245 hctx = blk_mq_map_queue(q, flush_rq->mq_ctx->cpu);
247 blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);
250 blk_mq_put_driver_tag_hctx(hctx, flush_rq);
251 flush_rq->internal_tag = -1;
255 running = &fq->flush_queue[fq->flush_running_idx];
256 BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
258 /* account completion of the flush request */
259 fq->flush_running_idx ^= 1;
262 elv_completed_request(q, flush_rq);
264 /* and push the waiting requests to the next stage */
265 list_for_each_entry_safe(rq, n, running, flush.list) {
266 unsigned int seq = blk_flush_cur_seq(rq);
268 BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
269 queued |= blk_flush_complete_seq(rq, fq, seq, error);
273 * Kick the queue to avoid stall for two cases:
274 * 1. Moving a request silently to empty queue_head may stall the
276 * 2. When flush request is running in non-queueable queue, the
277 * queue is hold. Restart the queue after flush request is finished
279 * This function is called from request completion path and calling
280 * directly into request_fn may confuse the driver. Always use
283 if (queued || fq->flush_queue_delayed) {
285 blk_run_queue_async(q);
287 fq->flush_queue_delayed = 0;
289 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
293 * blk_kick_flush - consider issuing flush request
294 * @q: request_queue being kicked
296 * @flags: cmd_flags of the original request
298 * Flush related states of @q have changed, consider issuing flush request.
299 * Please read the comment at the top of this file for more info.
302 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
305 * %true if flush was issued, %false otherwise.
307 static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
310 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
311 struct request *first_rq =
312 list_first_entry(pending, struct request, flush.list);
313 struct request *flush_rq = fq->flush_rq;
315 /* C1 described at the top of this file */
316 if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
321 * For blk-mq + scheduling, we can risk having all driver tags
322 * assigned to empty flushes, and we deadlock if we are expecting
323 * other requests to make progress. Don't defer for that case.
325 if (!list_empty(&fq->flush_data_in_flight) &&
326 !(q->mq_ops && q->elevator) &&
328 fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
332 * Issue flush and toggle pending_idx. This makes pending_idx
333 * different from running_idx, which means flush is in flight.
335 fq->flush_pending_idx ^= 1;
337 blk_rq_init(q, flush_rq);
340 * In case of none scheduler, borrow tag from the first request
341 * since they can't be in flight at the same time. And acquire
342 * the tag's ownership for flush req.
344 * In case of IO scheduler, flush rq need to borrow scheduler tag
345 * just for cheating put/get driver tag.
348 struct blk_mq_hw_ctx *hctx;
350 flush_rq->mq_ctx = first_rq->mq_ctx;
353 fq->orig_rq = first_rq;
354 flush_rq->tag = first_rq->tag;
355 hctx = blk_mq_map_queue(q, first_rq->mq_ctx->cpu);
356 blk_mq_tag_set_rq(hctx, first_rq->tag, flush_rq);
358 flush_rq->internal_tag = first_rq->internal_tag;
362 flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;
363 flush_rq->cmd_flags |= (flags & REQ_DRV) | (flags & REQ_FAILFAST_MASK);
364 flush_rq->rq_flags |= RQF_FLUSH_SEQ;
365 flush_rq->rq_disk = first_rq->rq_disk;
366 flush_rq->end_io = flush_end_io;
368 return blk_flush_queue_rq(flush_rq, false);
371 static void flush_data_end_io(struct request *rq, blk_status_t error)
373 struct request_queue *q = rq->q;
374 struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL);
376 lockdep_assert_held(q->queue_lock);
379 * Updating q->in_flight[] here for making this tag usable
380 * early. Because in blk_queue_start_tag(),
381 * q->in_flight[BLK_RW_ASYNC] is used to limit async I/O and
382 * reserve tags for sync I/O.
384 * More importantly this way can avoid the following I/O
387 * - suppose there are 40 fua requests comming to flush queue
388 * and queue depth is 31
389 * - 30 rqs are scheduled then blk_queue_start_tag() can't alloc
390 * tag for async I/O any more
391 * - all the 30 rqs are completed before FLUSH_PENDING_TIMEOUT
392 * and flush_data_end_io() is called
393 * - the other rqs still can't go ahead if not updating
394 * q->in_flight[BLK_RW_ASYNC] here, meantime these rqs
395 * are held in flush data queue and make no progress of
396 * handling post flush rq
397 * - only after the post flush rq is handled, all these rqs
401 elv_completed_request(q, rq);
403 /* for avoiding double accounting */
404 rq->rq_flags &= ~RQF_STARTED;
407 * After populating an empty queue, kick it to avoid stall. Read
408 * the comment in flush_end_io().
410 if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))
411 blk_run_queue_async(q);
414 static void mq_flush_data_end_io(struct request *rq, blk_status_t error)
416 struct request_queue *q = rq->q;
417 struct blk_mq_hw_ctx *hctx;
418 struct blk_mq_ctx *ctx = rq->mq_ctx;
420 struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
422 hctx = blk_mq_map_queue(q, ctx->cpu);
425 WARN_ON(rq->tag < 0);
426 blk_mq_put_driver_tag_hctx(hctx, rq);
430 * After populating an empty queue, kick it to avoid stall. Read
431 * the comment in flush_end_io().
433 spin_lock_irqsave(&fq->mq_flush_lock, flags);
434 blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);
435 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
437 blk_mq_sched_restart(hctx);
441 * blk_insert_flush - insert a new PREFLUSH/FUA request
442 * @rq: request to insert
444 * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
445 * or __blk_mq_run_hw_queue() to dispatch request.
446 * @rq is being submitted. Analyze what needs to be done and put it on the
449 void blk_insert_flush(struct request *rq)
451 struct request_queue *q = rq->q;
452 unsigned long fflags = q->queue_flags; /* may change, cache */
453 unsigned int policy = blk_flush_policy(fflags, rq);
454 struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
457 lockdep_assert_held(q->queue_lock);
460 * @policy now records what operations need to be done. Adjust
461 * REQ_PREFLUSH and FUA for the driver.
463 rq->cmd_flags &= ~REQ_PREFLUSH;
464 if (!(fflags & (1UL << QUEUE_FLAG_FUA)))
465 rq->cmd_flags &= ~REQ_FUA;
468 * REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any
469 * of those flags, we have to set REQ_SYNC to avoid skewing
470 * the request accounting.
472 rq->cmd_flags |= REQ_SYNC;
475 * An empty flush handed down from a stacking driver may
476 * translate into nothing if the underlying device does not
477 * advertise a write-back cache. In this case, simply
478 * complete the request.
482 blk_mq_end_request(rq, 0);
484 __blk_end_request(rq, 0, 0);
488 BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
491 * If there's data but flush is not necessary, the request can be
492 * processed directly without going through flush machinery. Queue
493 * for normal execution.
495 if ((policy & REQ_FSEQ_DATA) &&
496 !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
498 blk_mq_request_bypass_insert(rq, false);
500 list_add_tail(&rq->queuelist, &q->queue_head);
505 * @rq should go through flush machinery. Mark it part of flush
506 * sequence and submit for further processing.
508 memset(&rq->flush, 0, sizeof(rq->flush));
509 INIT_LIST_HEAD(&rq->flush.list);
510 rq->rq_flags |= RQF_FLUSH_SEQ;
511 rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
513 rq->end_io = mq_flush_data_end_io;
515 spin_lock_irq(&fq->mq_flush_lock);
516 blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
517 spin_unlock_irq(&fq->mq_flush_lock);
520 rq->end_io = flush_data_end_io;
522 blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
526 * blkdev_issue_flush - queue a flush
527 * @bdev: blockdev to issue flush for
528 * @gfp_mask: memory allocation flags (for bio_alloc)
529 * @error_sector: error sector
532 * Issue a flush for the block device in question. Caller can supply
533 * room for storing the error offset in case of a flush error, if they
536 int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
537 sector_t *error_sector)
539 struct request_queue *q;
543 if (bdev->bd_disk == NULL)
546 q = bdev_get_queue(bdev);
551 * some block devices may not have their queue correctly set up here
552 * (e.g. loop device without a backing file) and so issuing a flush
553 * here will panic. Ensure there is a request function before issuing
556 if (!q->make_request_fn)
559 bio = bio_alloc(gfp_mask, 0);
560 bio_set_dev(bio, bdev);
561 bio->bi_opf = REQ_OP_WRITE | REQ_PREFLUSH;
563 ret = submit_bio_wait(bio);
566 * The driver must store the error location in ->bi_sector, if
567 * it supports it. For non-stacked drivers, this should be
568 * copied from blk_rq_pos(rq).
571 *error_sector = bio->bi_iter.bi_sector;
576 EXPORT_SYMBOL(blkdev_issue_flush);
578 struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
579 int node, int cmd_size, gfp_t flags)
581 struct blk_flush_queue *fq;
582 int rq_sz = sizeof(struct request);
584 fq = kzalloc_node(sizeof(*fq), flags, node);
589 spin_lock_init(&fq->mq_flush_lock);
591 rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
592 fq->flush_rq = kzalloc_node(rq_sz, flags, node);
596 INIT_LIST_HEAD(&fq->flush_queue[0]);
597 INIT_LIST_HEAD(&fq->flush_queue[1]);
598 INIT_LIST_HEAD(&fq->flush_data_in_flight);
608 void blk_free_flush_queue(struct blk_flush_queue *fq)
610 /* bio based request queue hasn't flush queue */