1 // SPDX-License-Identifier: GPL-2.0-only
3 * linux/kernel/printk.c
5 * Copyright (C) 1991, 1992 Linus Torvalds
7 * Modified to make sys_syslog() more flexible: added commands to
8 * return the last 4k of kernel messages, regardless of whether
9 * they've been read or not. Added option to suppress kernel printk's
10 * to the console. Added hook for sending the console messages
11 * elsewhere, in preparation for a serial line console (someday).
13 * Modified for sysctl support, 1/8/97, Chris Horn.
14 * Fixed SMP synchronization, 08/08/99, Manfred Spraul
15 * manfred@colorfullife.com
16 * Rewrote bits to get rid of console_lock
17 * 01Mar01 Andrew Morton
20 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
22 #include <linux/kernel.h>
24 #include <linux/tty.h>
25 #include <linux/tty_driver.h>
26 #include <linux/console.h>
27 #include <linux/init.h>
28 #include <linux/jiffies.h>
29 #include <linux/nmi.h>
30 #include <linux/module.h>
31 #include <linux/moduleparam.h>
32 #include <linux/delay.h>
33 #include <linux/smp.h>
34 #include <linux/security.h>
35 #include <linux/memblock.h>
36 #include <linux/syscalls.h>
37 #include <linux/crash_core.h>
38 #include <linux/ratelimit.h>
39 #include <linux/kmsg_dump.h>
40 #include <linux/syslog.h>
41 #include <linux/cpu.h>
42 #include <linux/rculist.h>
43 #include <linux/poll.h>
44 #include <linux/irq_work.h>
45 #include <linux/ctype.h>
46 #include <linux/uio.h>
47 #include <linux/sched/clock.h>
48 #include <linux/sched/debug.h>
49 #include <linux/sched/task_stack.h>
51 #include <linux/uaccess.h>
52 #include <asm/sections.h>
54 #include <trace/events/initcall.h>
55 #define CREATE_TRACE_POINTS
56 #include <trace/events/printk.h>
58 #include "printk_ringbuffer.h"
59 #include "console_cmdline.h"
63 int console_printk[4] = {
64 CONSOLE_LOGLEVEL_DEFAULT, /* console_loglevel */
65 MESSAGE_LOGLEVEL_DEFAULT, /* default_message_loglevel */
66 CONSOLE_LOGLEVEL_MIN, /* minimum_console_loglevel */
67 CONSOLE_LOGLEVEL_DEFAULT, /* default_console_loglevel */
69 EXPORT_SYMBOL_GPL(console_printk);
71 atomic_t ignore_console_lock_warning __read_mostly = ATOMIC_INIT(0);
72 EXPORT_SYMBOL(ignore_console_lock_warning);
74 EXPORT_TRACEPOINT_SYMBOL_GPL(console);
77 * Low level drivers may need that to know if they can schedule in
78 * their unblank() callback or not. So let's export it.
81 EXPORT_SYMBOL(oops_in_progress);
84 * console_mutex protects console_list updates and console->flags updates.
85 * The flags are synchronized only for consoles that are registered, i.e.
86 * accessible via the console list.
88 static DEFINE_MUTEX(console_mutex);
91 * console_sem protects updates to console->seq
92 * and also provides serialization for console printing.
94 static DEFINE_SEMAPHORE(console_sem, 1);
95 HLIST_HEAD(console_list);
96 EXPORT_SYMBOL_GPL(console_list);
97 DEFINE_STATIC_SRCU(console_srcu);
100 * System may need to suppress printk message under certain
101 * circumstances, like after kernel panic happens.
103 int __read_mostly suppress_printk;
105 #ifdef CONFIG_LOCKDEP
106 static struct lockdep_map console_lock_dep_map = {
107 .name = "console_lock"
110 void lockdep_assert_console_list_lock_held(void)
112 lockdep_assert_held(&console_mutex);
114 EXPORT_SYMBOL(lockdep_assert_console_list_lock_held);
117 #ifdef CONFIG_DEBUG_LOCK_ALLOC
118 bool console_srcu_read_lock_is_held(void)
120 return srcu_read_lock_held(&console_srcu);
122 EXPORT_SYMBOL(console_srcu_read_lock_is_held);
125 enum devkmsg_log_bits {
126 __DEVKMSG_LOG_BIT_ON = 0,
127 __DEVKMSG_LOG_BIT_OFF,
128 __DEVKMSG_LOG_BIT_LOCK,
131 enum devkmsg_log_masks {
132 DEVKMSG_LOG_MASK_ON = BIT(__DEVKMSG_LOG_BIT_ON),
133 DEVKMSG_LOG_MASK_OFF = BIT(__DEVKMSG_LOG_BIT_OFF),
134 DEVKMSG_LOG_MASK_LOCK = BIT(__DEVKMSG_LOG_BIT_LOCK),
137 /* Keep both the 'on' and 'off' bits clear, i.e. ratelimit by default: */
138 #define DEVKMSG_LOG_MASK_DEFAULT 0
140 static unsigned int __read_mostly devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
142 static int __control_devkmsg(char *str)
149 len = str_has_prefix(str, "on");
151 devkmsg_log = DEVKMSG_LOG_MASK_ON;
155 len = str_has_prefix(str, "off");
157 devkmsg_log = DEVKMSG_LOG_MASK_OFF;
161 len = str_has_prefix(str, "ratelimit");
163 devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
170 static int __init control_devkmsg(char *str)
172 if (__control_devkmsg(str) < 0) {
173 pr_warn("printk.devkmsg: bad option string '%s'\n", str);
178 * Set sysctl string accordingly:
180 if (devkmsg_log == DEVKMSG_LOG_MASK_ON)
181 strcpy(devkmsg_log_str, "on");
182 else if (devkmsg_log == DEVKMSG_LOG_MASK_OFF)
183 strcpy(devkmsg_log_str, "off");
184 /* else "ratelimit" which is set by default. */
187 * Sysctl cannot change it anymore. The kernel command line setting of
188 * this parameter is to force the setting to be permanent throughout the
189 * runtime of the system. This is a precation measure against userspace
190 * trying to be a smarta** and attempting to change it up on us.
192 devkmsg_log |= DEVKMSG_LOG_MASK_LOCK;
196 __setup("printk.devkmsg=", control_devkmsg);
198 char devkmsg_log_str[DEVKMSG_STR_MAX_SIZE] = "ratelimit";
199 #if defined(CONFIG_PRINTK) && defined(CONFIG_SYSCTL)
200 int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write,
201 void *buffer, size_t *lenp, loff_t *ppos)
203 char old_str[DEVKMSG_STR_MAX_SIZE];
208 if (devkmsg_log & DEVKMSG_LOG_MASK_LOCK)
212 strncpy(old_str, devkmsg_log_str, DEVKMSG_STR_MAX_SIZE);
215 err = proc_dostring(table, write, buffer, lenp, ppos);
220 err = __control_devkmsg(devkmsg_log_str);
223 * Do not accept an unknown string OR a known string with
226 if (err < 0 || (err + 1 != *lenp)) {
228 /* ... and restore old setting. */
230 strncpy(devkmsg_log_str, old_str, DEVKMSG_STR_MAX_SIZE);
238 #endif /* CONFIG_PRINTK && CONFIG_SYSCTL */
241 * console_list_lock - Lock the console list
243 * For console list or console->flags updates
245 void console_list_lock(void)
248 * In unregister_console() and console_force_preferred_locked(),
249 * synchronize_srcu() is called with the console_list_lock held.
250 * Therefore it is not allowed that the console_list_lock is taken
251 * with the srcu_lock held.
253 * Detecting if this context is really in the read-side critical
254 * section is only possible if the appropriate debug options are
257 WARN_ON_ONCE(debug_lockdep_rcu_enabled() &&
258 srcu_read_lock_held(&console_srcu));
260 mutex_lock(&console_mutex);
262 EXPORT_SYMBOL(console_list_lock);
265 * console_list_unlock - Unlock the console list
267 * Counterpart to console_list_lock()
269 void console_list_unlock(void)
271 mutex_unlock(&console_mutex);
273 EXPORT_SYMBOL(console_list_unlock);
276 * console_srcu_read_lock - Register a new reader for the
277 * SRCU-protected console list
279 * Use for_each_console_srcu() to iterate the console list
281 * Context: Any context.
282 * Return: A cookie to pass to console_srcu_read_unlock().
284 int console_srcu_read_lock(void)
286 return srcu_read_lock_nmisafe(&console_srcu);
288 EXPORT_SYMBOL(console_srcu_read_lock);
291 * console_srcu_read_unlock - Unregister an old reader from
292 * the SRCU-protected console list
293 * @cookie: cookie returned from console_srcu_read_lock()
295 * Counterpart to console_srcu_read_lock()
297 void console_srcu_read_unlock(int cookie)
299 srcu_read_unlock_nmisafe(&console_srcu, cookie);
301 EXPORT_SYMBOL(console_srcu_read_unlock);
304 * Helper macros to handle lockdep when locking/unlocking console_sem. We use
305 * macros instead of functions so that _RET_IP_ contains useful information.
307 #define down_console_sem() do { \
309 mutex_acquire(&console_lock_dep_map, 0, 0, _RET_IP_);\
312 static int __down_trylock_console_sem(unsigned long ip)
318 * Here and in __up_console_sem() we need to be in safe mode,
319 * because spindump/WARN/etc from under console ->lock will
320 * deadlock in printk()->down_trylock_console_sem() otherwise.
322 printk_safe_enter_irqsave(flags);
323 lock_failed = down_trylock(&console_sem);
324 printk_safe_exit_irqrestore(flags);
328 mutex_acquire(&console_lock_dep_map, 0, 1, ip);
331 #define down_trylock_console_sem() __down_trylock_console_sem(_RET_IP_)
333 static void __up_console_sem(unsigned long ip)
337 mutex_release(&console_lock_dep_map, ip);
339 printk_safe_enter_irqsave(flags);
341 printk_safe_exit_irqrestore(flags);
343 #define up_console_sem() __up_console_sem(_RET_IP_)
345 static bool panic_in_progress(void)
347 return unlikely(atomic_read(&panic_cpu) != PANIC_CPU_INVALID);
351 * This is used for debugging the mess that is the VT code by
352 * keeping track if we have the console semaphore held. It's
353 * definitely not the perfect debug tool (we don't know if _WE_
354 * hold it and are racing, but it helps tracking those weird code
355 * paths in the console code where we end up in places I want
356 * locked without the console semaphore held).
358 static int console_locked;
361 * Array of consoles built from command line options (console=)
364 #define MAX_CMDLINECONSOLES 8
366 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
368 static int preferred_console = -1;
369 int console_set_on_cmdline;
370 EXPORT_SYMBOL(console_set_on_cmdline);
372 /* Flag: console code may call schedule() */
373 static int console_may_schedule;
375 enum con_msg_format_flags {
376 MSG_FORMAT_DEFAULT = 0,
377 MSG_FORMAT_SYSLOG = (1 << 0),
380 static int console_msg_format = MSG_FORMAT_DEFAULT;
383 * The printk log buffer consists of a sequenced collection of records, each
384 * containing variable length message text. Every record also contains its
385 * own meta-data (@info).
387 * Every record meta-data carries the timestamp in microseconds, as well as
388 * the standard userspace syslog level and syslog facility. The usual kernel
389 * messages use LOG_KERN; userspace-injected messages always carry a matching
390 * syslog facility, by default LOG_USER. The origin of every message can be
391 * reliably determined that way.
393 * The human readable log message of a record is available in @text, the
394 * length of the message text in @text_len. The stored message is not
397 * Optionally, a record can carry a dictionary of properties (key/value
398 * pairs), to provide userspace with a machine-readable message context.
400 * Examples for well-defined, commonly used property names are:
401 * DEVICE=b12:8 device identifier
405 * +sound:card0 subsystem:devname
406 * SUBSYSTEM=pci driver-core subsystem name
408 * Valid characters in property names are [a-zA-Z0-9.-_]. Property names
409 * and values are terminated by a '\0' character.
411 * Example of record values:
412 * record.text_buf = "it's a line" (unterminated)
413 * record.info.seq = 56
414 * record.info.ts_nsec = 36863
415 * record.info.text_len = 11
416 * record.info.facility = 0 (LOG_KERN)
417 * record.info.flags = 0
418 * record.info.level = 3 (LOG_ERR)
419 * record.info.caller_id = 299 (task 299)
420 * record.info.dev_info.subsystem = "pci" (terminated)
421 * record.info.dev_info.device = "+pci:0000:00:01.0" (terminated)
423 * The 'struct printk_info' buffer must never be directly exported to
424 * userspace, it is a kernel-private implementation detail that might
425 * need to be changed in the future, when the requirements change.
427 * /dev/kmsg exports the structured data in the following line format:
428 * "<level>,<sequnum>,<timestamp>,<contflag>[,additional_values, ... ];<message text>\n"
430 * Users of the export format should ignore possible additional values
431 * separated by ',', and find the message after the ';' character.
433 * The optional key/value pairs are attached as continuation lines starting
434 * with a space character and terminated by a newline. All possible
435 * non-prinatable characters are escaped in the "\xff" notation.
438 /* syslog_lock protects syslog_* variables and write access to clear_seq. */
439 static DEFINE_MUTEX(syslog_lock);
443 * During panic, heavy printk by other CPUs can delay the
444 * panic and risk deadlock on console resources.
446 static int __read_mostly suppress_panic_printk;
448 DECLARE_WAIT_QUEUE_HEAD(log_wait);
449 /* All 3 protected by @syslog_lock. */
450 /* the next printk record to read by syslog(READ) or /proc/kmsg */
451 static u64 syslog_seq;
452 static size_t syslog_partial;
453 static bool syslog_time;
456 seqcount_latch_t latch;
461 * The next printk record to read after the last 'clear' command. There are
462 * two copies (updated with seqcount_latch) so that reads can locklessly
463 * access a valid value. Writers are synchronized by @syslog_lock.
465 static struct latched_seq clear_seq = {
466 .latch = SEQCNT_LATCH_ZERO(clear_seq.latch),
471 #define LOG_LEVEL(v) ((v) & 0x07)
472 #define LOG_FACILITY(v) ((v) >> 3 & 0xff)
475 #define LOG_ALIGN __alignof__(unsigned long)
476 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
477 #define LOG_BUF_LEN_MAX (u32)(1 << 31)
478 static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
479 static char *log_buf = __log_buf;
480 static u32 log_buf_len = __LOG_BUF_LEN;
483 * Define the average message size. This only affects the number of
484 * descriptors that will be available. Underestimating is better than
485 * overestimating (too many available descriptors is better than not enough).
487 #define PRB_AVGBITS 5 /* 32 character average length */
489 #if CONFIG_LOG_BUF_SHIFT <= PRB_AVGBITS
490 #error CONFIG_LOG_BUF_SHIFT value too small.
492 _DEFINE_PRINTKRB(printk_rb_static, CONFIG_LOG_BUF_SHIFT - PRB_AVGBITS,
493 PRB_AVGBITS, &__log_buf[0]);
495 static struct printk_ringbuffer printk_rb_dynamic;
497 struct printk_ringbuffer *prb = &printk_rb_static;
500 * We cannot access per-CPU data (e.g. per-CPU flush irq_work) before
501 * per_cpu_areas are initialised. This variable is set to true when
502 * it's safe to access per-CPU data.
504 static bool __printk_percpu_data_ready __ro_after_init;
506 bool printk_percpu_data_ready(void)
508 return __printk_percpu_data_ready;
511 /* Must be called under syslog_lock. */
512 static void latched_seq_write(struct latched_seq *ls, u64 val)
514 raw_write_seqcount_latch(&ls->latch);
516 raw_write_seqcount_latch(&ls->latch);
520 /* Can be called from any context. */
521 static u64 latched_seq_read_nolock(struct latched_seq *ls)
528 seq = raw_read_seqcount_latch(&ls->latch);
531 } while (raw_read_seqcount_latch_retry(&ls->latch, seq));
536 /* Return log buffer address */
537 char *log_buf_addr_get(void)
542 /* Return log buffer size */
543 u32 log_buf_len_get(void)
549 * Define how much of the log buffer we could take at maximum. The value
550 * must be greater than two. Note that only half of the buffer is available
551 * when the index points to the middle.
553 #define MAX_LOG_TAKE_PART 4
554 static const char trunc_msg[] = "<truncated>";
556 static void truncate_msg(u16 *text_len, u16 *trunc_msg_len)
559 * The message should not take the whole buffer. Otherwise, it might
560 * get removed too soon.
562 u32 max_text_len = log_buf_len / MAX_LOG_TAKE_PART;
564 if (*text_len > max_text_len)
565 *text_len = max_text_len;
567 /* enable the warning message (if there is room) */
568 *trunc_msg_len = strlen(trunc_msg);
569 if (*text_len >= *trunc_msg_len)
570 *text_len -= *trunc_msg_len;
575 int dmesg_restrict = IS_ENABLED(CONFIG_SECURITY_DMESG_RESTRICT);
577 static int syslog_action_restricted(int type)
582 * Unless restricted, we allow "read all" and "get buffer size"
585 return type != SYSLOG_ACTION_READ_ALL &&
586 type != SYSLOG_ACTION_SIZE_BUFFER;
589 static int check_syslog_permissions(int type, int source)
592 * If this is from /proc/kmsg and we've already opened it, then we've
593 * already done the capabilities checks at open time.
595 if (source == SYSLOG_FROM_PROC && type != SYSLOG_ACTION_OPEN)
598 if (syslog_action_restricted(type)) {
599 if (capable(CAP_SYSLOG))
602 * For historical reasons, accept CAP_SYS_ADMIN too, with
605 if (capable(CAP_SYS_ADMIN)) {
606 pr_warn_once("%s (%d): Attempt to access syslog with "
607 "CAP_SYS_ADMIN but no CAP_SYSLOG "
609 current->comm, task_pid_nr(current));
615 return security_syslog(type);
618 static void append_char(char **pp, char *e, char c)
624 static ssize_t info_print_ext_header(char *buf, size_t size,
625 struct printk_info *info)
627 u64 ts_usec = info->ts_nsec;
629 #ifdef CONFIG_PRINTK_CALLER
630 u32 id = info->caller_id;
632 snprintf(caller, sizeof(caller), ",caller=%c%u",
633 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
638 do_div(ts_usec, 1000);
640 return scnprintf(buf, size, "%u,%llu,%llu,%c%s;",
641 (info->facility << 3) | info->level, info->seq,
642 ts_usec, info->flags & LOG_CONT ? 'c' : '-', caller);
645 static ssize_t msg_add_ext_text(char *buf, size_t size,
646 const char *text, size_t text_len,
649 char *p = buf, *e = buf + size;
652 /* escape non-printable characters */
653 for (i = 0; i < text_len; i++) {
654 unsigned char c = text[i];
656 if (c < ' ' || c >= 127 || c == '\\')
657 p += scnprintf(p, e - p, "\\x%02x", c);
659 append_char(&p, e, c);
661 append_char(&p, e, endc);
666 static ssize_t msg_add_dict_text(char *buf, size_t size,
667 const char *key, const char *val)
669 size_t val_len = strlen(val);
675 len = msg_add_ext_text(buf, size, "", 0, ' '); /* dict prefix */
676 len += msg_add_ext_text(buf + len, size - len, key, strlen(key), '=');
677 len += msg_add_ext_text(buf + len, size - len, val, val_len, '\n');
682 static ssize_t msg_print_ext_body(char *buf, size_t size,
683 char *text, size_t text_len,
684 struct dev_printk_info *dev_info)
688 len = msg_add_ext_text(buf, size, text, text_len, '\n');
693 len += msg_add_dict_text(buf + len, size - len, "SUBSYSTEM",
694 dev_info->subsystem);
695 len += msg_add_dict_text(buf + len, size - len, "DEVICE",
701 /* /dev/kmsg - userspace message inject/listen interface */
702 struct devkmsg_user {
704 struct ratelimit_state rs;
706 struct printk_buffers pbufs;
709 static __printf(3, 4) __cold
710 int devkmsg_emit(int facility, int level, const char *fmt, ...)
716 r = vprintk_emit(facility, level, NULL, fmt, args);
722 static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
725 int level = default_message_loglevel;
726 int facility = 1; /* LOG_USER */
727 struct file *file = iocb->ki_filp;
728 struct devkmsg_user *user = file->private_data;
729 size_t len = iov_iter_count(from);
732 if (len > PRINTKRB_RECORD_MAX)
735 /* Ignore when user logging is disabled. */
736 if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
739 /* Ratelimit when not explicitly enabled. */
740 if (!(devkmsg_log & DEVKMSG_LOG_MASK_ON)) {
741 if (!___ratelimit(&user->rs, current->comm))
745 buf = kmalloc(len+1, GFP_KERNEL);
750 if (!copy_from_iter_full(buf, len, from)) {
756 * Extract and skip the syslog prefix <[0-9]*>. Coming from userspace
757 * the decimal value represents 32bit, the lower 3 bit are the log
758 * level, the rest are the log facility.
760 * If no prefix or no userspace facility is specified, we
761 * enforce LOG_USER, to be able to reliably distinguish
762 * kernel-generated messages from userspace-injected ones.
765 if (line[0] == '<') {
769 u = simple_strtoul(line + 1, &endp, 10);
770 if (endp && endp[0] == '>') {
771 level = LOG_LEVEL(u);
772 if (LOG_FACILITY(u) != 0)
773 facility = LOG_FACILITY(u);
779 devkmsg_emit(facility, level, "%s", line);
784 static ssize_t devkmsg_read(struct file *file, char __user *buf,
785 size_t count, loff_t *ppos)
787 struct devkmsg_user *user = file->private_data;
788 char *outbuf = &user->pbufs.outbuf[0];
789 struct printk_message pmsg = {
790 .pbufs = &user->pbufs,
794 ret = mutex_lock_interruptible(&user->lock);
798 if (!printk_get_next_message(&pmsg, atomic64_read(&user->seq), true, false)) {
799 if (file->f_flags & O_NONBLOCK) {
805 * Guarantee this task is visible on the waitqueue before
806 * checking the wake condition.
808 * The full memory barrier within set_current_state() of
809 * prepare_to_wait_event() pairs with the full memory barrier
810 * within wq_has_sleeper().
812 * This pairs with __wake_up_klogd:A.
814 ret = wait_event_interruptible(log_wait,
815 printk_get_next_message(&pmsg, atomic64_read(&user->seq), true,
816 false)); /* LMM(devkmsg_read:A) */
822 /* our last seen message is gone, return error and reset */
823 atomic64_set(&user->seq, pmsg.seq);
828 atomic64_set(&user->seq, pmsg.seq + 1);
830 if (pmsg.outbuf_len > count) {
835 if (copy_to_user(buf, outbuf, pmsg.outbuf_len)) {
839 ret = pmsg.outbuf_len;
841 mutex_unlock(&user->lock);
846 * Be careful when modifying this function!!!
848 * Only few operations are supported because the device works only with the
849 * entire variable length messages (records). Non-standard values are
850 * returned in the other cases and has been this way for quite some time.
851 * User space applications might depend on this behavior.
853 static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
855 struct devkmsg_user *user = file->private_data;
863 /* the first record */
864 atomic64_set(&user->seq, prb_first_valid_seq(prb));
868 * The first record after the last SYSLOG_ACTION_CLEAR,
869 * like issued by 'dmesg -c'. Reading /dev/kmsg itself
870 * changes no global state, and does not clear anything.
872 atomic64_set(&user->seq, latched_seq_read_nolock(&clear_seq));
875 /* after the last record */
876 atomic64_set(&user->seq, prb_next_seq(prb));
884 static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
886 struct devkmsg_user *user = file->private_data;
887 struct printk_info info;
890 poll_wait(file, &log_wait, wait);
892 if (prb_read_valid_info(prb, atomic64_read(&user->seq), &info, NULL)) {
893 /* return error when data has vanished underneath us */
894 if (info.seq != atomic64_read(&user->seq))
895 ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;
897 ret = EPOLLIN|EPOLLRDNORM;
903 static int devkmsg_open(struct inode *inode, struct file *file)
905 struct devkmsg_user *user;
908 if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
911 /* write-only does not need any file context */
912 if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
913 err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
919 user = kvmalloc(sizeof(struct devkmsg_user), GFP_KERNEL);
923 ratelimit_default_init(&user->rs);
924 ratelimit_set_flags(&user->rs, RATELIMIT_MSG_ON_RELEASE);
926 mutex_init(&user->lock);
928 atomic64_set(&user->seq, prb_first_valid_seq(prb));
930 file->private_data = user;
934 static int devkmsg_release(struct inode *inode, struct file *file)
936 struct devkmsg_user *user = file->private_data;
938 ratelimit_state_exit(&user->rs);
940 mutex_destroy(&user->lock);
945 const struct file_operations kmsg_fops = {
946 .open = devkmsg_open,
947 .read = devkmsg_read,
948 .write_iter = devkmsg_write,
949 .llseek = devkmsg_llseek,
950 .poll = devkmsg_poll,
951 .release = devkmsg_release,
954 #ifdef CONFIG_CRASH_CORE
956 * This appends the listed symbols to /proc/vmcore
958 * /proc/vmcore is used by various utilities, like crash and makedumpfile to
959 * obtain access to symbols that are otherwise very difficult to locate. These
960 * symbols are specifically used so that utilities can access and extract the
961 * dmesg log from a vmcore file after a crash.
963 void log_buf_vmcoreinfo_setup(void)
965 struct dev_printk_info *dev_info = NULL;
967 VMCOREINFO_SYMBOL(prb);
968 VMCOREINFO_SYMBOL(printk_rb_static);
969 VMCOREINFO_SYMBOL(clear_seq);
972 * Export struct size and field offsets. User space tools can
973 * parse it and detect any changes to structure down the line.
976 VMCOREINFO_STRUCT_SIZE(printk_ringbuffer);
977 VMCOREINFO_OFFSET(printk_ringbuffer, desc_ring);
978 VMCOREINFO_OFFSET(printk_ringbuffer, text_data_ring);
979 VMCOREINFO_OFFSET(printk_ringbuffer, fail);
981 VMCOREINFO_STRUCT_SIZE(prb_desc_ring);
982 VMCOREINFO_OFFSET(prb_desc_ring, count_bits);
983 VMCOREINFO_OFFSET(prb_desc_ring, descs);
984 VMCOREINFO_OFFSET(prb_desc_ring, infos);
985 VMCOREINFO_OFFSET(prb_desc_ring, head_id);
986 VMCOREINFO_OFFSET(prb_desc_ring, tail_id);
988 VMCOREINFO_STRUCT_SIZE(prb_desc);
989 VMCOREINFO_OFFSET(prb_desc, state_var);
990 VMCOREINFO_OFFSET(prb_desc, text_blk_lpos);
992 VMCOREINFO_STRUCT_SIZE(prb_data_blk_lpos);
993 VMCOREINFO_OFFSET(prb_data_blk_lpos, begin);
994 VMCOREINFO_OFFSET(prb_data_blk_lpos, next);
996 VMCOREINFO_STRUCT_SIZE(printk_info);
997 VMCOREINFO_OFFSET(printk_info, seq);
998 VMCOREINFO_OFFSET(printk_info, ts_nsec);
999 VMCOREINFO_OFFSET(printk_info, text_len);
1000 VMCOREINFO_OFFSET(printk_info, caller_id);
1001 VMCOREINFO_OFFSET(printk_info, dev_info);
1003 VMCOREINFO_STRUCT_SIZE(dev_printk_info);
1004 VMCOREINFO_OFFSET(dev_printk_info, subsystem);
1005 VMCOREINFO_LENGTH(printk_info_subsystem, sizeof(dev_info->subsystem));
1006 VMCOREINFO_OFFSET(dev_printk_info, device);
1007 VMCOREINFO_LENGTH(printk_info_device, sizeof(dev_info->device));
1009 VMCOREINFO_STRUCT_SIZE(prb_data_ring);
1010 VMCOREINFO_OFFSET(prb_data_ring, size_bits);
1011 VMCOREINFO_OFFSET(prb_data_ring, data);
1012 VMCOREINFO_OFFSET(prb_data_ring, head_lpos);
1013 VMCOREINFO_OFFSET(prb_data_ring, tail_lpos);
1015 VMCOREINFO_SIZE(atomic_long_t);
1016 VMCOREINFO_TYPE_OFFSET(atomic_long_t, counter);
1018 VMCOREINFO_STRUCT_SIZE(latched_seq);
1019 VMCOREINFO_OFFSET(latched_seq, val);
1023 /* requested log_buf_len from kernel cmdline */
1024 static unsigned long __initdata new_log_buf_len;
1026 /* we practice scaling the ring buffer by powers of 2 */
1027 static void __init log_buf_len_update(u64 size)
1029 if (size > (u64)LOG_BUF_LEN_MAX) {
1030 size = (u64)LOG_BUF_LEN_MAX;
1031 pr_err("log_buf over 2G is not supported.\n");
1035 size = roundup_pow_of_two(size);
1036 if (size > log_buf_len)
1037 new_log_buf_len = (unsigned long)size;
1040 /* save requested log_buf_len since it's too early to process it */
1041 static int __init log_buf_len_setup(char *str)
1048 size = memparse(str, &str);
1050 log_buf_len_update(size);
1054 early_param("log_buf_len", log_buf_len_setup);
1057 #define __LOG_CPU_MAX_BUF_LEN (1 << CONFIG_LOG_CPU_MAX_BUF_SHIFT)
1059 static void __init log_buf_add_cpu(void)
1061 unsigned int cpu_extra;
1064 * archs should set up cpu_possible_bits properly with
1065 * set_cpu_possible() after setup_arch() but just in
1066 * case lets ensure this is valid.
1068 if (num_possible_cpus() == 1)
1071 cpu_extra = (num_possible_cpus() - 1) * __LOG_CPU_MAX_BUF_LEN;
1073 /* by default this will only continue through for large > 64 CPUs */
1074 if (cpu_extra <= __LOG_BUF_LEN / 2)
1077 pr_info("log_buf_len individual max cpu contribution: %d bytes\n",
1078 __LOG_CPU_MAX_BUF_LEN);
1079 pr_info("log_buf_len total cpu_extra contributions: %d bytes\n",
1081 pr_info("log_buf_len min size: %d bytes\n", __LOG_BUF_LEN);
1083 log_buf_len_update(cpu_extra + __LOG_BUF_LEN);
1085 #else /* !CONFIG_SMP */
1086 static inline void log_buf_add_cpu(void) {}
1087 #endif /* CONFIG_SMP */
1089 static void __init set_percpu_data_ready(void)
1091 __printk_percpu_data_ready = true;
1094 static unsigned int __init add_to_rb(struct printk_ringbuffer *rb,
1095 struct printk_record *r)
1097 struct prb_reserved_entry e;
1098 struct printk_record dest_r;
1100 prb_rec_init_wr(&dest_r, r->info->text_len);
1102 if (!prb_reserve(&e, rb, &dest_r))
1105 memcpy(&dest_r.text_buf[0], &r->text_buf[0], r->info->text_len);
1106 dest_r.info->text_len = r->info->text_len;
1107 dest_r.info->facility = r->info->facility;
1108 dest_r.info->level = r->info->level;
1109 dest_r.info->flags = r->info->flags;
1110 dest_r.info->ts_nsec = r->info->ts_nsec;
1111 dest_r.info->caller_id = r->info->caller_id;
1112 memcpy(&dest_r.info->dev_info, &r->info->dev_info, sizeof(dest_r.info->dev_info));
1114 prb_final_commit(&e);
1116 return prb_record_text_space(&e);
1119 static char setup_text_buf[PRINTKRB_RECORD_MAX] __initdata;
1121 void __init setup_log_buf(int early)
1123 struct printk_info *new_infos;
1124 unsigned int new_descs_count;
1125 struct prb_desc *new_descs;
1126 struct printk_info info;
1127 struct printk_record r;
1128 unsigned int text_size;
1129 size_t new_descs_size;
1130 size_t new_infos_size;
1131 unsigned long flags;
1137 * Some archs call setup_log_buf() multiple times - first is very
1138 * early, e.g. from setup_arch(), and second - when percpu_areas
1142 set_percpu_data_ready();
1144 if (log_buf != __log_buf)
1147 if (!early && !new_log_buf_len)
1150 if (!new_log_buf_len)
1153 new_descs_count = new_log_buf_len >> PRB_AVGBITS;
1154 if (new_descs_count == 0) {
1155 pr_err("new_log_buf_len: %lu too small\n", new_log_buf_len);
1159 new_log_buf = memblock_alloc(new_log_buf_len, LOG_ALIGN);
1160 if (unlikely(!new_log_buf)) {
1161 pr_err("log_buf_len: %lu text bytes not available\n",
1166 new_descs_size = new_descs_count * sizeof(struct prb_desc);
1167 new_descs = memblock_alloc(new_descs_size, LOG_ALIGN);
1168 if (unlikely(!new_descs)) {
1169 pr_err("log_buf_len: %zu desc bytes not available\n",
1171 goto err_free_log_buf;
1174 new_infos_size = new_descs_count * sizeof(struct printk_info);
1175 new_infos = memblock_alloc(new_infos_size, LOG_ALIGN);
1176 if (unlikely(!new_infos)) {
1177 pr_err("log_buf_len: %zu info bytes not available\n",
1179 goto err_free_descs;
1182 prb_rec_init_rd(&r, &info, &setup_text_buf[0], sizeof(setup_text_buf));
1184 prb_init(&printk_rb_dynamic,
1185 new_log_buf, ilog2(new_log_buf_len),
1186 new_descs, ilog2(new_descs_count),
1189 local_irq_save(flags);
1191 log_buf_len = new_log_buf_len;
1192 log_buf = new_log_buf;
1193 new_log_buf_len = 0;
1195 free = __LOG_BUF_LEN;
1196 prb_for_each_record(0, &printk_rb_static, seq, &r) {
1197 text_size = add_to_rb(&printk_rb_dynamic, &r);
1198 if (text_size > free)
1204 prb = &printk_rb_dynamic;
1206 local_irq_restore(flags);
1209 * Copy any remaining messages that might have appeared from
1210 * NMI context after copying but before switching to the
1213 prb_for_each_record(seq, &printk_rb_static, seq, &r) {
1214 text_size = add_to_rb(&printk_rb_dynamic, &r);
1215 if (text_size > free)
1221 if (seq != prb_next_seq(&printk_rb_static)) {
1222 pr_err("dropped %llu messages\n",
1223 prb_next_seq(&printk_rb_static) - seq);
1226 pr_info("log_buf_len: %u bytes\n", log_buf_len);
1227 pr_info("early log buf free: %u(%u%%)\n",
1228 free, (free * 100) / __LOG_BUF_LEN);
1232 memblock_free(new_descs, new_descs_size);
1234 memblock_free(new_log_buf, new_log_buf_len);
1237 static bool __read_mostly ignore_loglevel;
1239 static int __init ignore_loglevel_setup(char *str)
1241 ignore_loglevel = true;
1242 pr_info("debug: ignoring loglevel setting.\n");
1247 early_param("ignore_loglevel", ignore_loglevel_setup);
1248 module_param(ignore_loglevel, bool, S_IRUGO | S_IWUSR);
1249 MODULE_PARM_DESC(ignore_loglevel,
1250 "ignore loglevel setting (prints all kernel messages to the console)");
1252 static bool suppress_message_printing(int level)
1254 return (level >= console_loglevel && !ignore_loglevel);
1257 #ifdef CONFIG_BOOT_PRINTK_DELAY
1259 static int boot_delay; /* msecs delay after each printk during bootup */
1260 static unsigned long long loops_per_msec; /* based on boot_delay */
1262 static int __init boot_delay_setup(char *str)
1266 lpj = preset_lpj ? preset_lpj : 1000000; /* some guess */
1267 loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
1269 get_option(&str, &boot_delay);
1270 if (boot_delay > 10 * 1000)
1273 pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
1274 "HZ: %d, loops_per_msec: %llu\n",
1275 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
1278 early_param("boot_delay", boot_delay_setup);
1280 static void boot_delay_msec(int level)
1282 unsigned long long k;
1283 unsigned long timeout;
1285 if ((boot_delay == 0 || system_state >= SYSTEM_RUNNING)
1286 || suppress_message_printing(level)) {
1290 k = (unsigned long long)loops_per_msec * boot_delay;
1292 timeout = jiffies + msecs_to_jiffies(boot_delay);
1297 * use (volatile) jiffies to prevent
1298 * compiler reduction; loop termination via jiffies
1299 * is secondary and may or may not happen.
1301 if (time_after(jiffies, timeout))
1303 touch_nmi_watchdog();
1307 static inline void boot_delay_msec(int level)
1312 static bool printk_time = IS_ENABLED(CONFIG_PRINTK_TIME);
1313 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
1315 static size_t print_syslog(unsigned int level, char *buf)
1317 return sprintf(buf, "<%u>", level);
1320 static size_t print_time(u64 ts, char *buf)
1322 unsigned long rem_nsec = do_div(ts, 1000000000);
1324 return sprintf(buf, "[%5lu.%06lu]",
1325 (unsigned long)ts, rem_nsec / 1000);
1328 #ifdef CONFIG_PRINTK_CALLER
1329 static size_t print_caller(u32 id, char *buf)
1333 snprintf(caller, sizeof(caller), "%c%u",
1334 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
1335 return sprintf(buf, "[%6s]", caller);
1338 #define print_caller(id, buf) 0
1341 static size_t info_print_prefix(const struct printk_info *info, bool syslog,
1342 bool time, char *buf)
1347 len = print_syslog((info->facility << 3) | info->level, buf);
1350 len += print_time(info->ts_nsec, buf + len);
1352 len += print_caller(info->caller_id, buf + len);
1354 if (IS_ENABLED(CONFIG_PRINTK_CALLER) || time) {
1363 * Prepare the record for printing. The text is shifted within the given
1364 * buffer to avoid a need for another one. The following operations are
1367 * - Add prefix for each line.
1368 * - Drop truncated lines that no longer fit into the buffer.
1369 * - Add the trailing newline that has been removed in vprintk_store().
1370 * - Add a string terminator.
1372 * Since the produced string is always terminated, the maximum possible
1373 * return value is @r->text_buf_size - 1;
1375 * Return: The length of the updated/prepared text, including the added
1376 * prefixes and the newline. The terminator is not counted. The dropped
1377 * line(s) are not counted.
1379 static size_t record_print_text(struct printk_record *r, bool syslog,
1382 size_t text_len = r->info->text_len;
1383 size_t buf_size = r->text_buf_size;
1384 char *text = r->text_buf;
1385 char prefix[PRINTK_PREFIX_MAX];
1386 bool truncated = false;
1393 * If the message was truncated because the buffer was not large
1394 * enough, treat the available text as if it were the full text.
1396 if (text_len > buf_size)
1397 text_len = buf_size;
1399 prefix_len = info_print_prefix(r->info, syslog, time, prefix);
1402 * @text_len: bytes of unprocessed text
1403 * @line_len: bytes of current line _without_ newline
1404 * @text: pointer to beginning of current line
1405 * @len: number of bytes prepared in r->text_buf
1408 next = memchr(text, '\n', text_len);
1410 line_len = next - text;
1412 /* Drop truncated line(s). */
1415 line_len = text_len;
1419 * Truncate the text if there is not enough space to add the
1420 * prefix and a trailing newline and a terminator.
1422 if (len + prefix_len + text_len + 1 + 1 > buf_size) {
1423 /* Drop even the current line if no space. */
1424 if (len + prefix_len + line_len + 1 + 1 > buf_size)
1427 text_len = buf_size - len - prefix_len - 1 - 1;
1431 memmove(text + prefix_len, text, text_len);
1432 memcpy(text, prefix, prefix_len);
1435 * Increment the prepared length to include the text and
1436 * prefix that were just moved+copied. Also increment for the
1437 * newline at the end of this line. If this is the last line,
1438 * there is no newline, but it will be added immediately below.
1440 len += prefix_len + line_len + 1;
1441 if (text_len == line_len) {
1443 * This is the last line. Add the trailing newline
1444 * removed in vprintk_store().
1446 text[prefix_len + line_len] = '\n';
1451 * Advance beyond the added prefix and the related line with
1454 text += prefix_len + line_len + 1;
1457 * The remaining text has only decreased by the line with its
1460 * Note that @text_len can become zero. It happens when @text
1461 * ended with a newline (either due to truncation or the
1462 * original string ending with "\n\n"). The loop is correctly
1463 * repeated and (if not truncated) an empty line with a prefix
1466 text_len -= line_len + 1;
1470 * If a buffer was provided, it will be terminated. Space for the
1471 * string terminator is guaranteed to be available. The terminator is
1472 * not counted in the return value.
1475 r->text_buf[len] = 0;
1480 static size_t get_record_print_text_size(struct printk_info *info,
1481 unsigned int line_count,
1482 bool syslog, bool time)
1484 char prefix[PRINTK_PREFIX_MAX];
1487 prefix_len = info_print_prefix(info, syslog, time, prefix);
1490 * Each line will be preceded with a prefix. The intermediate
1491 * newlines are already within the text, but a final trailing
1492 * newline will be added.
1494 return ((prefix_len * line_count) + info->text_len + 1);
1498 * Beginning with @start_seq, find the first record where it and all following
1499 * records up to (but not including) @max_seq fit into @size.
1501 * @max_seq is simply an upper bound and does not need to exist. If the caller
1502 * does not require an upper bound, -1 can be used for @max_seq.
1504 static u64 find_first_fitting_seq(u64 start_seq, u64 max_seq, size_t size,
1505 bool syslog, bool time)
1507 struct printk_info info;
1508 unsigned int line_count;
1512 /* Determine the size of the records up to @max_seq. */
1513 prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
1514 if (info.seq >= max_seq)
1516 len += get_record_print_text_size(&info, line_count, syslog, time);
1520 * Adjust the upper bound for the next loop to avoid subtracting
1521 * lengths that were never added.
1527 * Move first record forward until length fits into the buffer. Ignore
1528 * newest messages that were not counted in the above cycle. Messages
1529 * might appear and get lost in the meantime. This is a best effort
1530 * that prevents an infinite loop that could occur with a retry.
1532 prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
1533 if (len <= size || info.seq >= max_seq)
1535 len -= get_record_print_text_size(&info, line_count, syslog, time);
1541 /* The caller is responsible for making sure @size is greater than 0. */
1542 static int syslog_print(char __user *buf, int size)
1544 struct printk_info info;
1545 struct printk_record r;
1550 text = kmalloc(PRINTK_MESSAGE_MAX, GFP_KERNEL);
1554 prb_rec_init_rd(&r, &info, text, PRINTK_MESSAGE_MAX);
1556 mutex_lock(&syslog_lock);
1559 * Wait for the @syslog_seq record to be available. @syslog_seq may
1560 * change while waiting.
1565 mutex_unlock(&syslog_lock);
1567 * Guarantee this task is visible on the waitqueue before
1568 * checking the wake condition.
1570 * The full memory barrier within set_current_state() of
1571 * prepare_to_wait_event() pairs with the full memory barrier
1572 * within wq_has_sleeper().
1574 * This pairs with __wake_up_klogd:A.
1576 len = wait_event_interruptible(log_wait,
1577 prb_read_valid(prb, seq, NULL)); /* LMM(syslog_print:A) */
1578 mutex_lock(&syslog_lock);
1582 } while (syslog_seq != seq);
1585 * Copy records that fit into the buffer. The above cycle makes sure
1586 * that the first record is always available.
1593 if (!prb_read_valid(prb, syslog_seq, &r))
1596 if (r.info->seq != syslog_seq) {
1597 /* message is gone, move to next valid one */
1598 syslog_seq = r.info->seq;
1603 * To keep reading/counting partial line consistent,
1604 * use printk_time value as of the beginning of a line.
1606 if (!syslog_partial)
1607 syslog_time = printk_time;
1609 skip = syslog_partial;
1610 n = record_print_text(&r, true, syslog_time);
1611 if (n - syslog_partial <= size) {
1612 /* message fits into buffer, move forward */
1613 syslog_seq = r.info->seq + 1;
1614 n -= syslog_partial;
1617 /* partial read(), remember position */
1619 syslog_partial += n;
1626 mutex_unlock(&syslog_lock);
1627 err = copy_to_user(buf, text + skip, n);
1628 mutex_lock(&syslog_lock);
1641 mutex_unlock(&syslog_lock);
1646 static int syslog_print_all(char __user *buf, int size, bool clear)
1648 struct printk_info info;
1649 struct printk_record r;
1655 text = kmalloc(PRINTK_MESSAGE_MAX, GFP_KERNEL);
1661 * Find first record that fits, including all following records,
1662 * into the user-provided buffer for this dump.
1664 seq = find_first_fitting_seq(latched_seq_read_nolock(&clear_seq), -1,
1667 prb_rec_init_rd(&r, &info, text, PRINTK_MESSAGE_MAX);
1669 prb_for_each_record(seq, prb, seq, &r) {
1672 textlen = record_print_text(&r, true, time);
1674 if (len + textlen > size) {
1679 if (copy_to_user(buf + len, text, textlen))
1689 mutex_lock(&syslog_lock);
1690 latched_seq_write(&clear_seq, seq);
1691 mutex_unlock(&syslog_lock);
1698 static void syslog_clear(void)
1700 mutex_lock(&syslog_lock);
1701 latched_seq_write(&clear_seq, prb_next_seq(prb));
1702 mutex_unlock(&syslog_lock);
1705 int do_syslog(int type, char __user *buf, int len, int source)
1707 struct printk_info info;
1709 static int saved_console_loglevel = LOGLEVEL_DEFAULT;
1712 error = check_syslog_permissions(type, source);
1717 case SYSLOG_ACTION_CLOSE: /* Close log */
1719 case SYSLOG_ACTION_OPEN: /* Open log */
1721 case SYSLOG_ACTION_READ: /* Read from log */
1722 if (!buf || len < 0)
1726 if (!access_ok(buf, len))
1728 error = syslog_print(buf, len);
1730 /* Read/clear last kernel messages */
1731 case SYSLOG_ACTION_READ_CLEAR:
1734 /* Read last kernel messages */
1735 case SYSLOG_ACTION_READ_ALL:
1736 if (!buf || len < 0)
1740 if (!access_ok(buf, len))
1742 error = syslog_print_all(buf, len, clear);
1744 /* Clear ring buffer */
1745 case SYSLOG_ACTION_CLEAR:
1748 /* Disable logging to console */
1749 case SYSLOG_ACTION_CONSOLE_OFF:
1750 if (saved_console_loglevel == LOGLEVEL_DEFAULT)
1751 saved_console_loglevel = console_loglevel;
1752 console_loglevel = minimum_console_loglevel;
1754 /* Enable logging to console */
1755 case SYSLOG_ACTION_CONSOLE_ON:
1756 if (saved_console_loglevel != LOGLEVEL_DEFAULT) {
1757 console_loglevel = saved_console_loglevel;
1758 saved_console_loglevel = LOGLEVEL_DEFAULT;
1761 /* Set level of messages printed to console */
1762 case SYSLOG_ACTION_CONSOLE_LEVEL:
1763 if (len < 1 || len > 8)
1765 if (len < minimum_console_loglevel)
1766 len = minimum_console_loglevel;
1767 console_loglevel = len;
1768 /* Implicitly re-enable logging to console */
1769 saved_console_loglevel = LOGLEVEL_DEFAULT;
1771 /* Number of chars in the log buffer */
1772 case SYSLOG_ACTION_SIZE_UNREAD:
1773 mutex_lock(&syslog_lock);
1774 if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) {
1775 /* No unread messages. */
1776 mutex_unlock(&syslog_lock);
1779 if (info.seq != syslog_seq) {
1780 /* messages are gone, move to first one */
1781 syslog_seq = info.seq;
1784 if (source == SYSLOG_FROM_PROC) {
1786 * Short-cut for poll(/"proc/kmsg") which simply checks
1787 * for pending data, not the size; return the count of
1788 * records, not the length.
1790 error = prb_next_seq(prb) - syslog_seq;
1792 bool time = syslog_partial ? syslog_time : printk_time;
1793 unsigned int line_count;
1796 prb_for_each_info(syslog_seq, prb, seq, &info,
1798 error += get_record_print_text_size(&info, line_count,
1802 error -= syslog_partial;
1804 mutex_unlock(&syslog_lock);
1806 /* Size of the log buffer */
1807 case SYSLOG_ACTION_SIZE_BUFFER:
1808 error = log_buf_len;
1818 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
1820 return do_syslog(type, buf, len, SYSLOG_FROM_READER);
1824 * Special console_lock variants that help to reduce the risk of soft-lockups.
1825 * They allow to pass console_lock to another printk() call using a busy wait.
1828 #ifdef CONFIG_LOCKDEP
1829 static struct lockdep_map console_owner_dep_map = {
1830 .name = "console_owner"
1834 static DEFINE_RAW_SPINLOCK(console_owner_lock);
1835 static struct task_struct *console_owner;
1836 static bool console_waiter;
1839 * console_lock_spinning_enable - mark beginning of code where another
1840 * thread might safely busy wait
1842 * This basically converts console_lock into a spinlock. This marks
1843 * the section where the console_lock owner can not sleep, because
1844 * there may be a waiter spinning (like a spinlock). Also it must be
1845 * ready to hand over the lock at the end of the section.
1847 static void console_lock_spinning_enable(void)
1849 raw_spin_lock(&console_owner_lock);
1850 console_owner = current;
1851 raw_spin_unlock(&console_owner_lock);
1853 /* The waiter may spin on us after setting console_owner */
1854 spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
1858 * console_lock_spinning_disable_and_check - mark end of code where another
1859 * thread was able to busy wait and check if there is a waiter
1860 * @cookie: cookie returned from console_srcu_read_lock()
1862 * This is called at the end of the section where spinning is allowed.
1863 * It has two functions. First, it is a signal that it is no longer
1864 * safe to start busy waiting for the lock. Second, it checks if
1865 * there is a busy waiter and passes the lock rights to her.
1867 * Important: Callers lose both the console_lock and the SRCU read lock if
1868 * there was a busy waiter. They must not touch items synchronized by
1869 * console_lock or SRCU read lock in this case.
1871 * Return: 1 if the lock rights were passed, 0 otherwise.
1873 static int console_lock_spinning_disable_and_check(int cookie)
1877 raw_spin_lock(&console_owner_lock);
1878 waiter = READ_ONCE(console_waiter);
1879 console_owner = NULL;
1880 raw_spin_unlock(&console_owner_lock);
1883 spin_release(&console_owner_dep_map, _THIS_IP_);
1887 /* The waiter is now free to continue */
1888 WRITE_ONCE(console_waiter, false);
1890 spin_release(&console_owner_dep_map, _THIS_IP_);
1893 * Preserve lockdep lock ordering. Release the SRCU read lock before
1894 * releasing the console_lock.
1896 console_srcu_read_unlock(cookie);
1899 * Hand off console_lock to waiter. The waiter will perform
1900 * the up(). After this, the waiter is the console_lock owner.
1902 mutex_release(&console_lock_dep_map, _THIS_IP_);
1907 * console_trylock_spinning - try to get console_lock by busy waiting
1909 * This allows to busy wait for the console_lock when the current
1910 * owner is running in specially marked sections. It means that
1911 * the current owner is running and cannot reschedule until it
1912 * is ready to lose the lock.
1914 * Return: 1 if we got the lock, 0 othrewise
1916 static int console_trylock_spinning(void)
1918 struct task_struct *owner = NULL;
1921 unsigned long flags;
1923 if (console_trylock())
1927 * It's unsafe to spin once a panic has begun. If we are the
1928 * panic CPU, we may have already halted the owner of the
1929 * console_sem. If we are not the panic CPU, then we should
1930 * avoid taking console_sem, so the panic CPU has a better
1931 * chance of cleanly acquiring it later.
1933 if (panic_in_progress())
1936 printk_safe_enter_irqsave(flags);
1938 raw_spin_lock(&console_owner_lock);
1939 owner = READ_ONCE(console_owner);
1940 waiter = READ_ONCE(console_waiter);
1941 if (!waiter && owner && owner != current) {
1942 WRITE_ONCE(console_waiter, true);
1945 raw_spin_unlock(&console_owner_lock);
1948 * If there is an active printk() writing to the
1949 * consoles, instead of having it write our data too,
1950 * see if we can offload that load from the active
1951 * printer, and do some printing ourselves.
1952 * Go into a spin only if there isn't already a waiter
1953 * spinning, and there is an active printer, and
1954 * that active printer isn't us (recursive printk?).
1957 printk_safe_exit_irqrestore(flags);
1961 /* We spin waiting for the owner to release us */
1962 spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
1963 /* Owner will clear console_waiter on hand off */
1964 while (READ_ONCE(console_waiter))
1966 spin_release(&console_owner_dep_map, _THIS_IP_);
1968 printk_safe_exit_irqrestore(flags);
1970 * The owner passed the console lock to us.
1971 * Since we did not spin on console lock, annotate
1972 * this as a trylock. Otherwise lockdep will
1975 mutex_acquire(&console_lock_dep_map, 0, 1, _THIS_IP_);
1981 * Recursion is tracked separately on each CPU. If NMIs are supported, an
1982 * additional NMI context per CPU is also separately tracked. Until per-CPU
1983 * is available, a separate "early tracking" is performed.
1985 static DEFINE_PER_CPU(u8, printk_count);
1986 static u8 printk_count_early;
1987 #ifdef CONFIG_HAVE_NMI
1988 static DEFINE_PER_CPU(u8, printk_count_nmi);
1989 static u8 printk_count_nmi_early;
1993 * Recursion is limited to keep the output sane. printk() should not require
1994 * more than 1 level of recursion (allowing, for example, printk() to trigger
1995 * a WARN), but a higher value is used in case some printk-internal errors
1996 * exist, such as the ringbuffer validation checks failing.
1998 #define PRINTK_MAX_RECURSION 3
2001 * Return a pointer to the dedicated counter for the CPU+context of the
2004 static u8 *__printk_recursion_counter(void)
2006 #ifdef CONFIG_HAVE_NMI
2008 if (printk_percpu_data_ready())
2009 return this_cpu_ptr(&printk_count_nmi);
2010 return &printk_count_nmi_early;
2013 if (printk_percpu_data_ready())
2014 return this_cpu_ptr(&printk_count);
2015 return &printk_count_early;
2019 * Enter recursion tracking. Interrupts are disabled to simplify tracking.
2020 * The caller must check the boolean return value to see if the recursion is
2021 * allowed. On failure, interrupts are not disabled.
2023 * @recursion_ptr must be a variable of type (u8 *) and is the same variable
2024 * that is passed to printk_exit_irqrestore().
2026 #define printk_enter_irqsave(recursion_ptr, flags) \
2028 bool success = true; \
2030 typecheck(u8 *, recursion_ptr); \
2031 local_irq_save(flags); \
2032 (recursion_ptr) = __printk_recursion_counter(); \
2033 if (*(recursion_ptr) > PRINTK_MAX_RECURSION) { \
2034 local_irq_restore(flags); \
2037 (*(recursion_ptr))++; \
2042 /* Exit recursion tracking, restoring interrupts. */
2043 #define printk_exit_irqrestore(recursion_ptr, flags) \
2045 typecheck(u8 *, recursion_ptr); \
2046 (*(recursion_ptr))--; \
2047 local_irq_restore(flags); \
2050 int printk_delay_msec __read_mostly;
2052 static inline void printk_delay(int level)
2054 boot_delay_msec(level);
2056 if (unlikely(printk_delay_msec)) {
2057 int m = printk_delay_msec;
2061 touch_nmi_watchdog();
2066 static inline u32 printk_caller_id(void)
2068 return in_task() ? task_pid_nr(current) :
2069 0x80000000 + smp_processor_id();
2073 * printk_parse_prefix - Parse level and control flags.
2075 * @text: The terminated text message.
2076 * @level: A pointer to the current level value, will be updated.
2077 * @flags: A pointer to the current printk_info flags, will be updated.
2079 * @level may be NULL if the caller is not interested in the parsed value.
2080 * Otherwise the variable pointed to by @level must be set to
2081 * LOGLEVEL_DEFAULT in order to be updated with the parsed value.
2083 * @flags may be NULL if the caller is not interested in the parsed value.
2084 * Otherwise the variable pointed to by @flags will be OR'd with the parsed
2087 * Return: The length of the parsed level and control flags.
2089 u16 printk_parse_prefix(const char *text, int *level,
2090 enum printk_info_flags *flags)
2096 kern_level = printk_get_level(text);
2100 switch (kern_level) {
2102 if (level && *level == LOGLEVEL_DEFAULT)
2103 *level = kern_level - '0';
2105 case 'c': /* KERN_CONT */
2118 static u16 printk_sprint(char *text, u16 size, int facility,
2119 enum printk_info_flags *flags, const char *fmt,
2124 text_len = vscnprintf(text, size, fmt, args);
2126 /* Mark and strip a trailing newline. */
2127 if (text_len && text[text_len - 1] == '\n') {
2129 *flags |= LOG_NEWLINE;
2132 /* Strip log level and control flags. */
2133 if (facility == 0) {
2136 prefix_len = printk_parse_prefix(text, NULL, NULL);
2138 text_len -= prefix_len;
2139 memmove(text, text + prefix_len, text_len);
2143 trace_console(text, text_len);
2149 int vprintk_store(int facility, int level,
2150 const struct dev_printk_info *dev_info,
2151 const char *fmt, va_list args)
2153 struct prb_reserved_entry e;
2154 enum printk_info_flags flags = 0;
2155 struct printk_record r;
2156 unsigned long irqflags;
2157 u16 trunc_msg_len = 0;
2167 if (!printk_enter_irqsave(recursion_ptr, irqflags))
2171 * Since the duration of printk() can vary depending on the message
2172 * and state of the ringbuffer, grab the timestamp now so that it is
2173 * close to the call of printk(). This provides a more deterministic
2174 * timestamp with respect to the caller.
2176 ts_nsec = local_clock();
2178 caller_id = printk_caller_id();
2181 * The sprintf needs to come first since the syslog prefix might be
2182 * passed in as a parameter. An extra byte must be reserved so that
2183 * later the vscnprintf() into the reserved buffer has room for the
2184 * terminating '\0', which is not counted by vsnprintf().
2186 va_copy(args2, args);
2187 reserve_size = vsnprintf(&prefix_buf[0], sizeof(prefix_buf), fmt, args2) + 1;
2190 if (reserve_size > PRINTKRB_RECORD_MAX)
2191 reserve_size = PRINTKRB_RECORD_MAX;
2193 /* Extract log level or control flags. */
2195 printk_parse_prefix(&prefix_buf[0], &level, &flags);
2197 if (level == LOGLEVEL_DEFAULT)
2198 level = default_message_loglevel;
2201 flags |= LOG_NEWLINE;
2203 if (flags & LOG_CONT) {
2204 prb_rec_init_wr(&r, reserve_size);
2205 if (prb_reserve_in_last(&e, prb, &r, caller_id, PRINTKRB_RECORD_MAX)) {
2206 text_len = printk_sprint(&r.text_buf[r.info->text_len], reserve_size,
2207 facility, &flags, fmt, args);
2208 r.info->text_len += text_len;
2210 if (flags & LOG_NEWLINE) {
2211 r.info->flags |= LOG_NEWLINE;
2212 prb_final_commit(&e);
2223 * Explicitly initialize the record before every prb_reserve() call.
2224 * prb_reserve_in_last() and prb_reserve() purposely invalidate the
2225 * structure when they fail.
2227 prb_rec_init_wr(&r, reserve_size);
2228 if (!prb_reserve(&e, prb, &r)) {
2229 /* truncate the message if it is too long for empty buffer */
2230 truncate_msg(&reserve_size, &trunc_msg_len);
2232 prb_rec_init_wr(&r, reserve_size + trunc_msg_len);
2233 if (!prb_reserve(&e, prb, &r))
2238 text_len = printk_sprint(&r.text_buf[0], reserve_size, facility, &flags, fmt, args);
2240 memcpy(&r.text_buf[text_len], trunc_msg, trunc_msg_len);
2241 r.info->text_len = text_len + trunc_msg_len;
2242 r.info->facility = facility;
2243 r.info->level = level & 7;
2244 r.info->flags = flags & 0x1f;
2245 r.info->ts_nsec = ts_nsec;
2246 r.info->caller_id = caller_id;
2248 memcpy(&r.info->dev_info, dev_info, sizeof(r.info->dev_info));
2250 /* A message without a trailing newline can be continued. */
2251 if (!(flags & LOG_NEWLINE))
2254 prb_final_commit(&e);
2256 ret = text_len + trunc_msg_len;
2258 printk_exit_irqrestore(recursion_ptr, irqflags);
2262 asmlinkage int vprintk_emit(int facility, int level,
2263 const struct dev_printk_info *dev_info,
2264 const char *fmt, va_list args)
2267 bool in_sched = false;
2269 /* Suppress unimportant messages after panic happens */
2270 if (unlikely(suppress_printk))
2273 if (unlikely(suppress_panic_printk) &&
2274 atomic_read(&panic_cpu) != raw_smp_processor_id())
2277 if (level == LOGLEVEL_SCHED) {
2278 level = LOGLEVEL_DEFAULT;
2282 printk_delay(level);
2284 printed_len = vprintk_store(facility, level, dev_info, fmt, args);
2286 /* If called from the scheduler, we can not call up(). */
2289 * The caller may be holding system-critical or
2290 * timing-sensitive locks. Disable preemption during
2291 * printing of all remaining records to all consoles so that
2292 * this context can return as soon as possible. Hopefully
2293 * another printk() caller will take over the printing.
2297 * Try to acquire and then immediately release the console
2298 * semaphore. The release will print out buffers. With the
2299 * spinning variant, this context tries to take over the
2300 * printing from another printing context.
2302 if (console_trylock_spinning())
2308 defer_console_output();
2314 EXPORT_SYMBOL(vprintk_emit);
2316 int vprintk_default(const char *fmt, va_list args)
2318 return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, fmt, args);
2320 EXPORT_SYMBOL_GPL(vprintk_default);
2322 asmlinkage __visible int _printk(const char *fmt, ...)
2327 va_start(args, fmt);
2328 r = vprintk(fmt, args);
2333 EXPORT_SYMBOL(_printk);
2335 static bool pr_flush(int timeout_ms, bool reset_on_progress);
2336 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress);
2338 #else /* CONFIG_PRINTK */
2340 #define printk_time false
2342 #define prb_read_valid(rb, seq, r) false
2343 #define prb_first_valid_seq(rb) 0
2344 #define prb_next_seq(rb) 0
2346 static u64 syslog_seq;
2348 static bool pr_flush(int timeout_ms, bool reset_on_progress) { return true; }
2349 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { return true; }
2351 #endif /* CONFIG_PRINTK */
2353 #ifdef CONFIG_EARLY_PRINTK
2354 struct console *early_console;
2356 asmlinkage __visible void early_printk(const char *fmt, ...)
2366 n = vscnprintf(buf, sizeof(buf), fmt, ap);
2369 early_console->write(early_console, buf, n);
2373 static void set_user_specified(struct console_cmdline *c, bool user_specified)
2375 if (!user_specified)
2379 * @c console was defined by the user on the command line.
2380 * Do not clear when added twice also by SPCR or the device tree.
2382 c->user_specified = true;
2383 /* At least one console defined by the user on the command line. */
2384 console_set_on_cmdline = 1;
2387 static int __add_preferred_console(const char *name, const short idx, char *options,
2388 char *brl_options, bool user_specified)
2390 struct console_cmdline *c;
2394 * We use a signed short index for struct console for device drivers to
2395 * indicate a not yet assigned index or port. However, a negative index
2396 * value is not valid for preferred console.
2402 * See if this tty is not yet registered, and
2403 * if we have a slot free.
2405 for (i = 0, c = console_cmdline;
2406 i < MAX_CMDLINECONSOLES && c->name[0];
2408 if (strcmp(c->name, name) == 0 && c->index == idx) {
2410 preferred_console = i;
2411 set_user_specified(c, user_specified);
2415 if (i == MAX_CMDLINECONSOLES)
2418 preferred_console = i;
2419 strscpy(c->name, name, sizeof(c->name));
2420 c->options = options;
2421 set_user_specified(c, user_specified);
2422 braille_set_options(c, brl_options);
2428 static int __init console_msg_format_setup(char *str)
2430 if (!strcmp(str, "syslog"))
2431 console_msg_format = MSG_FORMAT_SYSLOG;
2432 if (!strcmp(str, "default"))
2433 console_msg_format = MSG_FORMAT_DEFAULT;
2436 __setup("console_msg_format=", console_msg_format_setup);
2439 * Set up a console. Called via do_early_param() in init/main.c
2440 * for each "console=" parameter in the boot command line.
2442 static int __init console_setup(char *str)
2444 char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for "ttyS" */
2445 char *s, *options, *brl_options = NULL;
2449 * console="" or console=null have been suggested as a way to
2450 * disable console output. Use ttynull that has been created
2451 * for exactly this purpose.
2453 if (str[0] == 0 || strcmp(str, "null") == 0) {
2454 __add_preferred_console("ttynull", 0, NULL, NULL, true);
2458 if (_braille_console_setup(&str, &brl_options))
2462 * Decode str into name, index, options.
2464 if (str[0] >= '0' && str[0] <= '9') {
2465 strcpy(buf, "ttyS");
2466 strncpy(buf + 4, str, sizeof(buf) - 5);
2468 strncpy(buf, str, sizeof(buf) - 1);
2470 buf[sizeof(buf) - 1] = 0;
2471 options = strchr(str, ',');
2475 if (!strcmp(str, "ttya"))
2476 strcpy(buf, "ttyS0");
2477 if (!strcmp(str, "ttyb"))
2478 strcpy(buf, "ttyS1");
2480 for (s = buf; *s; s++)
2481 if (isdigit(*s) || *s == ',')
2483 idx = simple_strtoul(s, NULL, 10);
2486 __add_preferred_console(buf, idx, options, brl_options, true);
2489 __setup("console=", console_setup);
2492 * add_preferred_console - add a device to the list of preferred consoles.
2493 * @name: device name
2494 * @idx: device index
2495 * @options: options for this console
2497 * The last preferred console added will be used for kernel messages
2498 * and stdin/out/err for init. Normally this is used by console_setup
2499 * above to handle user-supplied console arguments; however it can also
2500 * be used by arch-specific code either to override the user or more
2501 * commonly to provide a default console (ie from PROM variables) when
2502 * the user has not supplied one.
2504 int add_preferred_console(const char *name, const short idx, char *options)
2506 return __add_preferred_console(name, idx, options, NULL, false);
2509 bool console_suspend_enabled = true;
2510 EXPORT_SYMBOL(console_suspend_enabled);
2512 static int __init console_suspend_disable(char *str)
2514 console_suspend_enabled = false;
2517 __setup("no_console_suspend", console_suspend_disable);
2518 module_param_named(console_suspend, console_suspend_enabled,
2519 bool, S_IRUGO | S_IWUSR);
2520 MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
2521 " and hibernate operations");
2523 static bool printk_console_no_auto_verbose;
2525 void console_verbose(void)
2527 if (console_loglevel && !printk_console_no_auto_verbose)
2528 console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
2530 EXPORT_SYMBOL_GPL(console_verbose);
2532 module_param_named(console_no_auto_verbose, printk_console_no_auto_verbose, bool, 0644);
2533 MODULE_PARM_DESC(console_no_auto_verbose, "Disable console loglevel raise to highest on oops/panic/etc");
2536 * suspend_console - suspend the console subsystem
2538 * This disables printk() while we go into suspend states
2540 void suspend_console(void)
2542 struct console *con;
2544 if (!console_suspend_enabled)
2546 pr_info("Suspending console(s) (use no_console_suspend to debug)\n");
2547 pr_flush(1000, true);
2549 console_list_lock();
2550 for_each_console(con)
2551 console_srcu_write_flags(con, con->flags | CON_SUSPENDED);
2552 console_list_unlock();
2555 * Ensure that all SRCU list walks have completed. All printing
2556 * contexts must be able to see that they are suspended so that it
2557 * is guaranteed that all printing has stopped when this function
2560 synchronize_srcu(&console_srcu);
2563 void resume_console(void)
2565 struct console *con;
2567 if (!console_suspend_enabled)
2570 console_list_lock();
2571 for_each_console(con)
2572 console_srcu_write_flags(con, con->flags & ~CON_SUSPENDED);
2573 console_list_unlock();
2576 * Ensure that all SRCU list walks have completed. All printing
2577 * contexts must be able to see they are no longer suspended so
2578 * that they are guaranteed to wake up and resume printing.
2580 synchronize_srcu(&console_srcu);
2582 pr_flush(1000, true);
2586 * console_cpu_notify - print deferred console messages after CPU hotplug
2589 * If printk() is called from a CPU that is not online yet, the messages
2590 * will be printed on the console only if there are CON_ANYTIME consoles.
2591 * This function is called when a new CPU comes online (or fails to come
2592 * up) or goes offline.
2594 static int console_cpu_notify(unsigned int cpu)
2596 if (!cpuhp_tasks_frozen) {
2597 /* If trylock fails, someone else is doing the printing */
2598 if (console_trylock())
2605 * Return true if a panic is in progress on a remote CPU.
2607 * On true, the local CPU should immediately release any printing resources
2608 * that may be needed by the panic CPU.
2610 bool other_cpu_in_panic(void)
2612 if (!panic_in_progress())
2616 * We can use raw_smp_processor_id() here because it is impossible for
2617 * the task to be migrated to the panic_cpu, or away from it. If
2618 * panic_cpu has already been set, and we're not currently executing on
2619 * that CPU, then we never will be.
2621 return atomic_read(&panic_cpu) != raw_smp_processor_id();
2625 * console_lock - block the console subsystem from printing
2627 * Acquires a lock which guarantees that no consoles will
2628 * be in or enter their write() callback.
2630 * Can sleep, returns nothing.
2632 void console_lock(void)
2636 /* On panic, the console_lock must be left to the panic cpu. */
2637 while (other_cpu_in_panic())
2642 console_may_schedule = 1;
2644 EXPORT_SYMBOL(console_lock);
2647 * console_trylock - try to block the console subsystem from printing
2649 * Try to acquire a lock which guarantees that no consoles will
2650 * be in or enter their write() callback.
2652 * returns 1 on success, and 0 on failure to acquire the lock.
2654 int console_trylock(void)
2656 /* On panic, the console_lock must be left to the panic cpu. */
2657 if (other_cpu_in_panic())
2659 if (down_trylock_console_sem())
2662 console_may_schedule = 0;
2665 EXPORT_SYMBOL(console_trylock);
2667 int is_console_locked(void)
2669 return console_locked;
2671 EXPORT_SYMBOL(is_console_locked);
2674 * Check if the given console is currently capable and allowed to print
2677 * Requires the console_srcu_read_lock.
2679 static inline bool console_is_usable(struct console *con)
2681 short flags = console_srcu_read_flags(con);
2683 if (!(flags & CON_ENABLED))
2686 if ((flags & CON_SUSPENDED))
2693 * Console drivers may assume that per-cpu resources have been
2694 * allocated. So unless they're explicitly marked as being able to
2695 * cope (CON_ANYTIME) don't call them until this CPU is officially up.
2697 if (!cpu_online(raw_smp_processor_id()) && !(flags & CON_ANYTIME))
2703 static void __console_unlock(void)
2709 #ifdef CONFIG_PRINTK
2712 * Prepend the message in @pmsg->pbufs->outbuf with a "dropped message". This
2713 * is achieved by shifting the existing message over and inserting the dropped
2716 * @pmsg is the printk message to prepend.
2718 * @dropped is the dropped count to report in the dropped message.
2720 * If the message text in @pmsg->pbufs->outbuf does not have enough space for
2721 * the dropped message, the message text will be sufficiently truncated.
2723 * If @pmsg->pbufs->outbuf is modified, @pmsg->outbuf_len is updated.
2725 void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
2727 struct printk_buffers *pbufs = pmsg->pbufs;
2728 const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);
2729 const size_t outbuf_sz = sizeof(pbufs->outbuf);
2730 char *scratchbuf = &pbufs->scratchbuf[0];
2731 char *outbuf = &pbufs->outbuf[0];
2734 len = scnprintf(scratchbuf, scratchbuf_sz,
2735 "** %lu printk messages dropped **\n", dropped);
2738 * Make sure outbuf is sufficiently large before prepending.
2739 * Keep at least the prefix when the message must be truncated.
2740 * It is a rather theoretical problem when someone tries to
2741 * use a minimalist buffer.
2743 if (WARN_ON_ONCE(len + PRINTK_PREFIX_MAX >= outbuf_sz))
2746 if (pmsg->outbuf_len + len >= outbuf_sz) {
2747 /* Truncate the message, but keep it terminated. */
2748 pmsg->outbuf_len = outbuf_sz - (len + 1);
2749 outbuf[pmsg->outbuf_len] = 0;
2752 memmove(outbuf + len, outbuf, pmsg->outbuf_len + 1);
2753 memcpy(outbuf, scratchbuf, len);
2754 pmsg->outbuf_len += len;
2758 * Read and format the specified record (or a later record if the specified
2759 * record is not available).
2761 * @pmsg will contain the formatted result. @pmsg->pbufs must point to a
2762 * struct printk_buffers.
2764 * @seq is the record to read and format. If it is not available, the next
2765 * valid record is read.
2767 * @is_extended specifies if the message should be formatted for extended
2770 * @may_supress specifies if records may be skipped based on loglevel.
2772 * Returns false if no record is available. Otherwise true and all fields
2773 * of @pmsg are valid. (See the documentation of struct printk_message
2774 * for information about the @pmsg fields.)
2776 bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
2777 bool is_extended, bool may_suppress)
2779 static int panic_console_dropped;
2781 struct printk_buffers *pbufs = pmsg->pbufs;
2782 const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);
2783 const size_t outbuf_sz = sizeof(pbufs->outbuf);
2784 char *scratchbuf = &pbufs->scratchbuf[0];
2785 char *outbuf = &pbufs->outbuf[0];
2786 struct printk_info info;
2787 struct printk_record r;
2791 * Formatting extended messages requires a separate buffer, so use the
2792 * scratch buffer to read in the ringbuffer text.
2794 * Formatting normal messages is done in-place, so read the ringbuffer
2795 * text directly into the output buffer.
2798 prb_rec_init_rd(&r, &info, scratchbuf, scratchbuf_sz);
2800 prb_rec_init_rd(&r, &info, outbuf, outbuf_sz);
2802 if (!prb_read_valid(prb, seq, &r))
2805 pmsg->seq = r.info->seq;
2806 pmsg->dropped = r.info->seq - seq;
2809 * Check for dropped messages in panic here so that printk
2810 * suppression can occur as early as possible if necessary.
2812 if (pmsg->dropped &&
2813 panic_in_progress() &&
2814 panic_console_dropped++ > 10) {
2815 suppress_panic_printk = 1;
2816 pr_warn_once("Too many dropped messages. Suppress messages on non-panic CPUs to prevent livelock.\n");
2819 /* Skip record that has level above the console loglevel. */
2820 if (may_suppress && suppress_message_printing(r.info->level))
2824 len = info_print_ext_header(outbuf, outbuf_sz, r.info);
2825 len += msg_print_ext_body(outbuf + len, outbuf_sz - len,
2826 &r.text_buf[0], r.info->text_len, &r.info->dev_info);
2828 len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time);
2831 pmsg->outbuf_len = len;
2836 * Used as the printk buffers for non-panic, serialized console printing.
2837 * This is for legacy (!CON_NBCON) as well as all boot (CON_BOOT) consoles.
2838 * Its usage requires the console_lock held.
2840 struct printk_buffers printk_shared_pbufs;
2843 * Print one record for the given console. The record printed is whatever
2844 * record is the next available record for the given console.
2846 * @handover will be set to true if a printk waiter has taken over the
2847 * console_lock, in which case the caller is no longer holding both the
2848 * console_lock and the SRCU read lock. Otherwise it is set to false.
2850 * @cookie is the cookie from the SRCU read lock.
2852 * Returns false if the given console has no next record to print, otherwise
2855 * Requires the console_lock and the SRCU read lock.
2857 static bool console_emit_next_record(struct console *con, bool *handover, int cookie)
2859 bool is_extended = console_srcu_read_flags(con) & CON_EXTENDED;
2860 char *outbuf = &printk_shared_pbufs.outbuf[0];
2861 struct printk_message pmsg = {
2862 .pbufs = &printk_shared_pbufs,
2864 unsigned long flags;
2868 if (!printk_get_next_message(&pmsg, con->seq, is_extended, true))
2871 con->dropped += pmsg.dropped;
2873 /* Skip messages of formatted length 0. */
2874 if (pmsg.outbuf_len == 0) {
2875 con->seq = pmsg.seq + 1;
2879 if (con->dropped && !is_extended) {
2880 console_prepend_dropped(&pmsg, con->dropped);
2885 * While actively printing out messages, if another printk()
2886 * were to occur on another CPU, it may wait for this one to
2887 * finish. This task can not be preempted if there is a
2888 * waiter waiting to take over.
2890 * Interrupts are disabled because the hand over to a waiter
2891 * must not be interrupted until the hand over is completed
2892 * (@console_waiter is cleared).
2894 printk_safe_enter_irqsave(flags);
2895 console_lock_spinning_enable();
2897 /* Do not trace print latency. */
2898 stop_critical_timings();
2900 /* Write everything out to the hardware. */
2901 con->write(con, outbuf, pmsg.outbuf_len);
2903 start_critical_timings();
2905 con->seq = pmsg.seq + 1;
2907 *handover = console_lock_spinning_disable_and_check(cookie);
2908 printk_safe_exit_irqrestore(flags);
2915 static bool console_emit_next_record(struct console *con, bool *handover, int cookie)
2921 #endif /* CONFIG_PRINTK */
2924 * Print out all remaining records to all consoles.
2926 * @do_cond_resched is set by the caller. It can be true only in schedulable
2929 * @next_seq is set to the sequence number after the last available record.
2930 * The value is valid only when this function returns true. It means that all
2931 * usable consoles are completely flushed.
2933 * @handover will be set to true if a printk waiter has taken over the
2934 * console_lock, in which case the caller is no longer holding the
2935 * console_lock. Otherwise it is set to false.
2937 * Returns true when there was at least one usable console and all messages
2938 * were flushed to all usable consoles. A returned false informs the caller
2939 * that everything was not flushed (either there were no usable consoles or
2940 * another context has taken over printing or it is a panic situation and this
2941 * is not the panic CPU). Regardless the reason, the caller should assume it
2942 * is not useful to immediately try again.
2944 * Requires the console_lock.
2946 static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handover)
2948 bool any_usable = false;
2949 struct console *con;
2957 any_progress = false;
2959 cookie = console_srcu_read_lock();
2960 for_each_console_srcu(con) {
2963 if (!console_is_usable(con))
2967 progress = console_emit_next_record(con, handover, cookie);
2970 * If a handover has occurred, the SRCU read lock
2971 * is already released.
2976 /* Track the next of the highest seq flushed. */
2977 if (con->seq > *next_seq)
2978 *next_seq = con->seq;
2982 any_progress = true;
2984 /* Allow panic_cpu to take over the consoles safely. */
2985 if (other_cpu_in_panic())
2988 if (do_cond_resched)
2991 console_srcu_read_unlock(cookie);
2992 } while (any_progress);
2997 console_srcu_read_unlock(cookie);
3002 * console_unlock - unblock the console subsystem from printing
3004 * Releases the console_lock which the caller holds to block printing of
3005 * the console subsystem.
3007 * While the console_lock was held, console output may have been buffered
3008 * by printk(). If this is the case, console_unlock(); emits
3009 * the output prior to releasing the lock.
3011 * console_unlock(); may be called from any context.
3013 void console_unlock(void)
3015 bool do_cond_resched;
3021 * Console drivers are called with interrupts disabled, so
3022 * @console_may_schedule should be cleared before; however, we may
3023 * end up dumping a lot of lines, for example, if called from
3024 * console registration path, and should invoke cond_resched()
3025 * between lines if allowable. Not doing so can cause a very long
3026 * scheduling stall on a slow console leading to RCU stall and
3027 * softlockup warnings which exacerbate the issue with more
3028 * messages practically incapacitating the system. Therefore, create
3029 * a local to use for the printing loop.
3031 do_cond_resched = console_may_schedule;
3034 console_may_schedule = 0;
3036 flushed = console_flush_all(do_cond_resched, &next_seq, &handover);
3041 * Abort if there was a failure to flush all messages to all
3042 * usable consoles. Either it is not possible to flush (in
3043 * which case it would be an infinite loop of retrying) or
3044 * another context has taken over printing.
3050 * Some context may have added new records after
3051 * console_flush_all() but before unlocking the console.
3052 * Re-check if there is a new record to flush. If the trylock
3053 * fails, another context is already handling the printing.
3055 } while (prb_read_valid(prb, next_seq, NULL) && console_trylock());
3057 EXPORT_SYMBOL(console_unlock);
3060 * console_conditional_schedule - yield the CPU if required
3062 * If the console code is currently allowed to sleep, and
3063 * if this CPU should yield the CPU to another task, do
3066 * Must be called within console_lock();.
3068 void __sched console_conditional_schedule(void)
3070 if (console_may_schedule)
3073 EXPORT_SYMBOL(console_conditional_schedule);
3075 void console_unblank(void)
3077 bool found_unblank = false;
3082 * First check if there are any consoles implementing the unblank()
3083 * callback. If not, there is no reason to continue and take the
3084 * console lock, which in particular can be dangerous if
3085 * @oops_in_progress is set.
3087 cookie = console_srcu_read_lock();
3088 for_each_console_srcu(c) {
3089 if ((console_srcu_read_flags(c) & CON_ENABLED) && c->unblank) {
3090 found_unblank = true;
3094 console_srcu_read_unlock(cookie);
3099 * Stop console printing because the unblank() callback may
3100 * assume the console is not within its write() callback.
3102 * If @oops_in_progress is set, this may be an atomic context.
3103 * In that case, attempt a trylock as best-effort.
3105 if (oops_in_progress) {
3106 /* Semaphores are not NMI-safe. */
3111 * Attempting to trylock the console lock can deadlock
3112 * if another CPU was stopped while modifying the
3113 * semaphore. "Hope and pray" that this is not the
3114 * current situation.
3116 if (down_trylock_console_sem() != 0)
3122 console_may_schedule = 0;
3124 cookie = console_srcu_read_lock();
3125 for_each_console_srcu(c) {
3126 if ((console_srcu_read_flags(c) & CON_ENABLED) && c->unblank)
3129 console_srcu_read_unlock(cookie);
3133 if (!oops_in_progress)
3134 pr_flush(1000, true);
3138 * console_flush_on_panic - flush console content on panic
3139 * @mode: flush all messages in buffer or just the pending ones
3141 * Immediately output all pending messages no matter what.
3143 void console_flush_on_panic(enum con_flush_mode mode)
3149 * Ignore the console lock and flush out the messages. Attempting a
3150 * trylock would not be useful because:
3152 * - if it is contended, it must be ignored anyway
3153 * - console_lock() and console_trylock() block and fail
3154 * respectively in panic for non-panic CPUs
3155 * - semaphores are not NMI-safe
3159 * If another context is holding the console lock,
3160 * @console_may_schedule might be set. Clear it so that
3161 * this context does not call cond_resched() while flushing.
3163 console_may_schedule = 0;
3165 if (mode == CONSOLE_REPLAY_ALL) {
3171 seq = prb_first_valid_seq(prb);
3173 cookie = console_srcu_read_lock();
3174 for_each_console_srcu(c) {
3175 flags = console_srcu_read_flags(c);
3177 if (flags & CON_NBCON) {
3178 nbcon_seq_force(c, seq);
3181 * This is an unsynchronized assignment. On
3182 * panic legacy consoles are only best effort.
3187 console_srcu_read_unlock(cookie);
3190 console_flush_all(false, &next_seq, &handover);
3194 * Return the console tty driver structure and its associated index
3196 struct tty_driver *console_device(int *index)
3199 struct tty_driver *driver = NULL;
3203 * Take console_lock to serialize device() callback with
3204 * other console operations. For example, fg_console is
3205 * modified under console_lock when switching vt.
3209 cookie = console_srcu_read_lock();
3210 for_each_console_srcu(c) {
3213 driver = c->device(c, index);
3217 console_srcu_read_unlock(cookie);
3224 * Prevent further output on the passed console device so that (for example)
3225 * serial drivers can disable console output before suspending a port, and can
3226 * re-enable output afterwards.
3228 void console_stop(struct console *console)
3230 __pr_flush(console, 1000, true);
3231 console_list_lock();
3232 console_srcu_write_flags(console, console->flags & ~CON_ENABLED);
3233 console_list_unlock();
3236 * Ensure that all SRCU list walks have completed. All contexts must
3237 * be able to see that this console is disabled so that (for example)
3238 * the caller can suspend the port without risk of another context
3241 synchronize_srcu(&console_srcu);
3243 EXPORT_SYMBOL(console_stop);
3245 void console_start(struct console *console)
3247 console_list_lock();
3248 console_srcu_write_flags(console, console->flags | CON_ENABLED);
3249 console_list_unlock();
3250 __pr_flush(console, 1000, true);
3252 EXPORT_SYMBOL(console_start);
3254 static int __read_mostly keep_bootcon;
3256 static int __init keep_bootcon_setup(char *str)
3259 pr_info("debug: skip boot console de-registration.\n");
3264 early_param("keep_bootcon", keep_bootcon_setup);
3267 * This is called by register_console() to try to match
3268 * the newly registered console with any of the ones selected
3269 * by either the command line or add_preferred_console() and
3272 * Care need to be taken with consoles that are statically
3273 * enabled such as netconsole
3275 static int try_enable_preferred_console(struct console *newcon,
3276 bool user_specified)
3278 struct console_cmdline *c;
3281 for (i = 0, c = console_cmdline;
3282 i < MAX_CMDLINECONSOLES && c->name[0];
3284 if (c->user_specified != user_specified)
3286 if (!newcon->match ||
3287 newcon->match(newcon, c->name, c->index, c->options) != 0) {
3288 /* default matching */
3289 BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));
3290 if (strcmp(c->name, newcon->name) != 0)
3292 if (newcon->index >= 0 &&
3293 newcon->index != c->index)
3295 if (newcon->index < 0)
3296 newcon->index = c->index;
3298 if (_braille_register_console(newcon, c))
3301 if (newcon->setup &&
3302 (err = newcon->setup(newcon, c->options)) != 0)
3305 newcon->flags |= CON_ENABLED;
3306 if (i == preferred_console)
3307 newcon->flags |= CON_CONSDEV;
3312 * Some consoles, such as pstore and netconsole, can be enabled even
3313 * without matching. Accept the pre-enabled consoles only when match()
3314 * and setup() had a chance to be called.
3316 if (newcon->flags & CON_ENABLED && c->user_specified == user_specified)
3322 /* Try to enable the console unconditionally */
3323 static void try_enable_default_console(struct console *newcon)
3325 if (newcon->index < 0)
3328 if (newcon->setup && newcon->setup(newcon, NULL) != 0)
3331 newcon->flags |= CON_ENABLED;
3334 newcon->flags |= CON_CONSDEV;
3337 static void console_init_seq(struct console *newcon, bool bootcon_registered)
3339 struct console *con;
3342 if (newcon->flags & (CON_PRINTBUFFER | CON_BOOT)) {
3343 /* Get a consistent copy of @syslog_seq. */
3344 mutex_lock(&syslog_lock);
3345 newcon->seq = syslog_seq;
3346 mutex_unlock(&syslog_lock);
3348 /* Begin with next message added to ringbuffer. */
3349 newcon->seq = prb_next_seq(prb);
3352 * If any enabled boot consoles are due to be unregistered
3353 * shortly, some may not be caught up and may be the same
3354 * device as @newcon. Since it is not known which boot console
3355 * is the same device, flush all consoles and, if necessary,
3356 * start with the message of the enabled boot console that is
3357 * the furthest behind.
3359 if (bootcon_registered && !keep_bootcon) {
3361 * Hold the console_lock to stop console printing and
3362 * guarantee safe access to console->seq.
3367 * Flush all consoles and set the console to start at
3368 * the next unprinted sequence number.
3370 if (!console_flush_all(true, &newcon->seq, &handover)) {
3372 * Flushing failed. Just choose the lowest
3373 * sequence of the enabled boot consoles.
3377 * If there was a handover, this context no
3378 * longer holds the console_lock.
3383 newcon->seq = prb_next_seq(prb);
3384 for_each_console(con) {
3385 if ((con->flags & CON_BOOT) &&
3386 (con->flags & CON_ENABLED) &&
3387 con->seq < newcon->seq) {
3388 newcon->seq = con->seq;
3398 #define console_first() \
3399 hlist_entry(console_list.first, struct console, node)
3401 static int unregister_console_locked(struct console *console);
3404 * The console driver calls this routine during kernel initialization
3405 * to register the console printing procedure with printk() and to
3406 * print any messages that were printed by the kernel before the
3407 * console driver was initialized.
3409 * This can happen pretty early during the boot process (because of
3410 * early_printk) - sometimes before setup_arch() completes - be careful
3411 * of what kernel features are used - they may not be initialised yet.
3413 * There are two types of consoles - bootconsoles (early_printk) and
3414 * "real" consoles (everything which is not a bootconsole) which are
3415 * handled differently.
3416 * - Any number of bootconsoles can be registered at any time.
3417 * - As soon as a "real" console is registered, all bootconsoles
3418 * will be unregistered automatically.
3419 * - Once a "real" console is registered, any attempt to register a
3420 * bootconsoles will be rejected
3422 void register_console(struct console *newcon)
3424 struct console *con;
3425 bool bootcon_registered = false;
3426 bool realcon_registered = false;
3429 console_list_lock();
3431 for_each_console(con) {
3432 if (WARN(con == newcon, "console '%s%d' already registered\n",
3433 con->name, con->index)) {
3437 if (con->flags & CON_BOOT)
3438 bootcon_registered = true;
3440 realcon_registered = true;
3443 /* Do not register boot consoles when there already is a real one. */
3444 if ((newcon->flags & CON_BOOT) && realcon_registered) {
3445 pr_info("Too late to register bootconsole %s%d\n",
3446 newcon->name, newcon->index);
3450 if (newcon->flags & CON_NBCON) {
3452 * Ensure the nbcon console buffers can be allocated
3453 * before modifying any global data.
3455 if (!nbcon_alloc(newcon))
3460 * See if we want to enable this console driver by default.
3462 * Nope when a console is preferred by the command line, device
3465 * The first real console with tty binding (driver) wins. More
3466 * consoles might get enabled before the right one is found.
3468 * Note that a console with tty binding will have CON_CONSDEV
3469 * flag set and will be first in the list.
3471 if (preferred_console < 0) {
3472 if (hlist_empty(&console_list) || !console_first()->device ||
3473 console_first()->flags & CON_BOOT) {
3474 try_enable_default_console(newcon);
3478 /* See if this console matches one we selected on the command line */
3479 err = try_enable_preferred_console(newcon, true);
3481 /* If not, try to match against the platform default(s) */
3483 err = try_enable_preferred_console(newcon, false);
3485 /* printk() messages are not printed to the Braille console. */
3486 if (err || newcon->flags & CON_BRL) {
3487 if (newcon->flags & CON_NBCON)
3493 * If we have a bootconsole, and are switching to a real console,
3494 * don't print everything out again, since when the boot console, and
3495 * the real console are the same physical device, it's annoying to
3496 * see the beginning boot messages twice
3498 if (bootcon_registered &&
3499 ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
3500 newcon->flags &= ~CON_PRINTBUFFER;
3503 newcon->dropped = 0;
3504 console_init_seq(newcon, bootcon_registered);
3506 if (newcon->flags & CON_NBCON)
3510 * Put this console in the list - keep the
3511 * preferred driver at the head of the list.
3513 if (hlist_empty(&console_list)) {
3514 /* Ensure CON_CONSDEV is always set for the head. */
3515 newcon->flags |= CON_CONSDEV;
3516 hlist_add_head_rcu(&newcon->node, &console_list);
3518 } else if (newcon->flags & CON_CONSDEV) {
3519 /* Only the new head can have CON_CONSDEV set. */
3520 console_srcu_write_flags(console_first(), console_first()->flags & ~CON_CONSDEV);
3521 hlist_add_head_rcu(&newcon->node, &console_list);
3524 hlist_add_behind_rcu(&newcon->node, console_list.first);
3528 * No need to synchronize SRCU here! The caller does not rely
3529 * on all contexts being able to see the new console before
3530 * register_console() completes.
3533 console_sysfs_notify();
3536 * By unregistering the bootconsoles after we enable the real console
3537 * we get the "console xxx enabled" message on all the consoles -
3538 * boot consoles, real consoles, etc - this is to ensure that end
3539 * users know there might be something in the kernel's log buffer that
3540 * went to the bootconsole (that they do not see on the real console)
3542 con_printk(KERN_INFO, newcon, "enabled\n");
3543 if (bootcon_registered &&
3544 ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) &&
3546 struct hlist_node *tmp;
3548 hlist_for_each_entry_safe(con, tmp, &console_list, node) {
3549 if (con->flags & CON_BOOT)
3550 unregister_console_locked(con);
3554 console_list_unlock();
3556 EXPORT_SYMBOL(register_console);
3558 /* Must be called under console_list_lock(). */
3559 static int unregister_console_locked(struct console *console)
3563 lockdep_assert_console_list_lock_held();
3565 con_printk(KERN_INFO, console, "disabled\n");
3567 res = _braille_unregister_console(console);
3573 /* Disable it unconditionally */
3574 console_srcu_write_flags(console, console->flags & ~CON_ENABLED);
3576 if (!console_is_registered_locked(console))
3579 hlist_del_init_rcu(&console->node);
3583 * If this isn't the last console and it has CON_CONSDEV set, we
3584 * need to set it on the next preferred console.
3587 * The above makes no sense as there is no guarantee that the next
3588 * console has any device attached. Oh well....
3590 if (!hlist_empty(&console_list) && console->flags & CON_CONSDEV)
3591 console_srcu_write_flags(console_first(), console_first()->flags | CON_CONSDEV);
3594 * Ensure that all SRCU list walks have completed. All contexts
3595 * must not be able to see this console in the list so that any
3596 * exit/cleanup routines can be performed safely.
3598 synchronize_srcu(&console_srcu);
3600 if (console->flags & CON_NBCON)
3601 nbcon_free(console);
3603 console_sysfs_notify();
3606 res = console->exit(console);
3611 int unregister_console(struct console *console)
3615 console_list_lock();
3616 res = unregister_console_locked(console);
3617 console_list_unlock();
3620 EXPORT_SYMBOL(unregister_console);
3623 * console_force_preferred_locked - force a registered console preferred
3624 * @con: The registered console to force preferred.
3626 * Must be called under console_list_lock().
3628 void console_force_preferred_locked(struct console *con)
3630 struct console *cur_pref_con;
3632 if (!console_is_registered_locked(con))
3635 cur_pref_con = console_first();
3637 /* Already preferred? */
3638 if (cur_pref_con == con)
3642 * Delete, but do not re-initialize the entry. This allows the console
3643 * to continue to appear registered (via any hlist_unhashed_lockless()
3644 * checks), even though it was briefly removed from the console list.
3646 hlist_del_rcu(&con->node);
3649 * Ensure that all SRCU list walks have completed so that the console
3650 * can be added to the beginning of the console list and its forward
3651 * list pointer can be re-initialized.
3653 synchronize_srcu(&console_srcu);
3655 con->flags |= CON_CONSDEV;
3656 WARN_ON(!con->device);
3658 /* Only the new head can have CON_CONSDEV set. */
3659 console_srcu_write_flags(cur_pref_con, cur_pref_con->flags & ~CON_CONSDEV);
3660 hlist_add_head_rcu(&con->node, &console_list);
3662 EXPORT_SYMBOL(console_force_preferred_locked);
3665 * Initialize the console device. This is called *early*, so
3666 * we can't necessarily depend on lots of kernel help here.
3667 * Just do some early initializations, and do the complex setup
3670 void __init console_init(void)
3674 initcall_entry_t *ce;
3676 /* Setup the default TTY line discipline. */
3680 * set up the console device so that later boot sequences can
3681 * inform about problems etc..
3683 ce = __con_initcall_start;
3684 trace_initcall_level("console");
3685 while (ce < __con_initcall_end) {
3686 call = initcall_from_entry(ce);
3687 trace_initcall_start(call);
3689 trace_initcall_finish(call, ret);
3695 * Some boot consoles access data that is in the init section and which will
3696 * be discarded after the initcalls have been run. To make sure that no code
3697 * will access this data, unregister the boot consoles in a late initcall.
3699 * If for some reason, such as deferred probe or the driver being a loadable
3700 * module, the real console hasn't registered yet at this point, there will
3701 * be a brief interval in which no messages are logged to the console, which
3702 * makes it difficult to diagnose problems that occur during this time.
3704 * To mitigate this problem somewhat, only unregister consoles whose memory
3705 * intersects with the init section. Note that all other boot consoles will
3706 * get unregistered when the real preferred console is registered.
3708 static int __init printk_late_init(void)
3710 struct hlist_node *tmp;
3711 struct console *con;
3714 console_list_lock();
3715 hlist_for_each_entry_safe(con, tmp, &console_list, node) {
3716 if (!(con->flags & CON_BOOT))
3719 /* Check addresses that might be used for enabled consoles. */
3720 if (init_section_intersects(con, sizeof(*con)) ||
3721 init_section_contains(con->write, 0) ||
3722 init_section_contains(con->read, 0) ||
3723 init_section_contains(con->device, 0) ||
3724 init_section_contains(con->unblank, 0) ||
3725 init_section_contains(con->data, 0)) {
3727 * Please, consider moving the reported consoles out
3728 * of the init section.
3730 pr_warn("bootconsole [%s%d] uses init memory and must be disabled even before the real one is ready\n",
3731 con->name, con->index);
3732 unregister_console_locked(con);
3735 console_list_unlock();
3737 ret = cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD, "printk:dead", NULL,
3738 console_cpu_notify);
3740 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "printk:online",
3741 console_cpu_notify, NULL);
3743 printk_sysctl_init();
3746 late_initcall(printk_late_init);
3748 #if defined CONFIG_PRINTK
3749 /* If @con is specified, only wait for that console. Otherwise wait for all. */
3750 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress)
3752 unsigned long timeout_jiffies = msecs_to_jiffies(timeout_ms);
3753 unsigned long remaining_jiffies = timeout_jiffies;
3764 seq = prb_next_seq(prb);
3766 /* Flush the consoles so that records up to @seq are printed. */
3771 unsigned long begin_jiffies;
3772 unsigned long slept_jiffies;
3777 * Hold the console_lock to guarantee safe access to
3778 * console->seq. Releasing console_lock flushes more
3779 * records in case @seq is still not printed on all
3784 cookie = console_srcu_read_lock();
3785 for_each_console_srcu(c) {
3786 if (con && con != c)
3789 flags = console_srcu_read_flags(c);
3792 * If consoles are not usable, it cannot be expected
3793 * that they make forward progress, so only increment
3794 * @diff for usable consoles.
3796 if (!console_is_usable(c))
3799 if (flags & CON_NBCON) {
3800 printk_seq = nbcon_seq_read(c);
3802 printk_seq = c->seq;
3805 if (printk_seq < seq)
3806 diff += seq - printk_seq;
3808 console_srcu_read_unlock(cookie);
3810 if (diff != last_diff && reset_on_progress)
3811 remaining_jiffies = timeout_jiffies;
3815 /* Note: @diff is 0 if there are no usable consoles. */
3816 if (diff == 0 || remaining_jiffies == 0)
3819 /* msleep(1) might sleep much longer. Check time by jiffies. */
3820 begin_jiffies = jiffies;
3822 slept_jiffies = jiffies - begin_jiffies;
3824 remaining_jiffies -= min(slept_jiffies, remaining_jiffies);
3833 * pr_flush() - Wait for printing threads to catch up.
3835 * @timeout_ms: The maximum time (in ms) to wait.
3836 * @reset_on_progress: Reset the timeout if forward progress is seen.
3838 * A value of 0 for @timeout_ms means no waiting will occur. A value of -1
3839 * represents infinite waiting.
3841 * If @reset_on_progress is true, the timeout will be reset whenever any
3842 * printer has been seen to make some forward progress.
3844 * Context: Process context. May sleep while acquiring console lock.
3845 * Return: true if all usable printers are caught up.
3847 static bool pr_flush(int timeout_ms, bool reset_on_progress)
3849 return __pr_flush(NULL, timeout_ms, reset_on_progress);
3853 * Delayed printk version, for scheduler-internal messages:
3855 #define PRINTK_PENDING_WAKEUP 0x01
3856 #define PRINTK_PENDING_OUTPUT 0x02
3858 static DEFINE_PER_CPU(int, printk_pending);
3860 static void wake_up_klogd_work_func(struct irq_work *irq_work)
3862 int pending = this_cpu_xchg(printk_pending, 0);
3864 if (pending & PRINTK_PENDING_OUTPUT) {
3865 /* If trylock fails, someone else is doing the printing */
3866 if (console_trylock())
3870 if (pending & PRINTK_PENDING_WAKEUP)
3871 wake_up_interruptible(&log_wait);
3874 static DEFINE_PER_CPU(struct irq_work, wake_up_klogd_work) =
3875 IRQ_WORK_INIT_LAZY(wake_up_klogd_work_func);
3877 static void __wake_up_klogd(int val)
3879 if (!printk_percpu_data_ready())
3884 * Guarantee any new records can be seen by tasks preparing to wait
3885 * before this context checks if the wait queue is empty.
3887 * The full memory barrier within wq_has_sleeper() pairs with the full
3888 * memory barrier within set_current_state() of
3889 * prepare_to_wait_event(), which is called after ___wait_event() adds
3890 * the waiter but before it has checked the wait condition.
3892 * This pairs with devkmsg_read:A and syslog_print:A.
3894 if (wq_has_sleeper(&log_wait) || /* LMM(__wake_up_klogd:A) */
3895 (val & PRINTK_PENDING_OUTPUT)) {
3896 this_cpu_or(printk_pending, val);
3897 irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
3903 * wake_up_klogd - Wake kernel logging daemon
3905 * Use this function when new records have been added to the ringbuffer
3906 * and the console printing of those records has already occurred or is
3907 * known to be handled by some other context. This function will only
3908 * wake the logging daemon.
3910 * Context: Any context.
3912 void wake_up_klogd(void)
3914 __wake_up_klogd(PRINTK_PENDING_WAKEUP);
3918 * defer_console_output - Wake kernel logging daemon and trigger
3919 * console printing in a deferred context
3921 * Use this function when new records have been added to the ringbuffer,
3922 * this context is responsible for console printing those records, but
3923 * the current context is not allowed to perform the console printing.
3924 * Trigger an irq_work context to perform the console printing. This
3925 * function also wakes the logging daemon.
3927 * Context: Any context.
3929 void defer_console_output(void)
3932 * New messages may have been added directly to the ringbuffer
3933 * using vprintk_store(), so wake any waiters as well.
3935 __wake_up_klogd(PRINTK_PENDING_WAKEUP | PRINTK_PENDING_OUTPUT);
3938 void printk_trigger_flush(void)
3940 defer_console_output();
3943 int vprintk_deferred(const char *fmt, va_list args)
3945 return vprintk_emit(0, LOGLEVEL_SCHED, NULL, fmt, args);
3948 int _printk_deferred(const char *fmt, ...)
3953 va_start(args, fmt);
3954 r = vprintk_deferred(fmt, args);
3961 * printk rate limiting, lifted from the networking subsystem.
3963 * This enforces a rate limit: not more than 10 kernel messages
3964 * every 5s to make a denial-of-service attack impossible.
3966 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
3968 int __printk_ratelimit(const char *func)
3970 return ___ratelimit(&printk_ratelimit_state, func);
3972 EXPORT_SYMBOL(__printk_ratelimit);
3975 * printk_timed_ratelimit - caller-controlled printk ratelimiting
3976 * @caller_jiffies: pointer to caller's state
3977 * @interval_msecs: minimum interval between prints
3979 * printk_timed_ratelimit() returns true if more than @interval_msecs
3980 * milliseconds have elapsed since the last time printk_timed_ratelimit()
3983 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
3984 unsigned int interval_msecs)
3986 unsigned long elapsed = jiffies - *caller_jiffies;
3988 if (*caller_jiffies && elapsed <= msecs_to_jiffies(interval_msecs))
3991 *caller_jiffies = jiffies;
3994 EXPORT_SYMBOL(printk_timed_ratelimit);
3996 static DEFINE_SPINLOCK(dump_list_lock);
3997 static LIST_HEAD(dump_list);
4000 * kmsg_dump_register - register a kernel log dumper.
4001 * @dumper: pointer to the kmsg_dumper structure
4003 * Adds a kernel log dumper to the system. The dump callback in the
4004 * structure will be called when the kernel oopses or panics and must be
4005 * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
4007 int kmsg_dump_register(struct kmsg_dumper *dumper)
4009 unsigned long flags;
4012 /* The dump callback needs to be set */
4016 spin_lock_irqsave(&dump_list_lock, flags);
4017 /* Don't allow registering multiple times */
4018 if (!dumper->registered) {
4019 dumper->registered = 1;
4020 list_add_tail_rcu(&dumper->list, &dump_list);
4023 spin_unlock_irqrestore(&dump_list_lock, flags);
4027 EXPORT_SYMBOL_GPL(kmsg_dump_register);
4030 * kmsg_dump_unregister - unregister a kmsg dumper.
4031 * @dumper: pointer to the kmsg_dumper structure
4033 * Removes a dump device from the system. Returns zero on success and
4034 * %-EINVAL otherwise.
4036 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
4038 unsigned long flags;
4041 spin_lock_irqsave(&dump_list_lock, flags);
4042 if (dumper->registered) {
4043 dumper->registered = 0;
4044 list_del_rcu(&dumper->list);
4047 spin_unlock_irqrestore(&dump_list_lock, flags);
4052 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
4054 static bool always_kmsg_dump;
4055 module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);
4057 const char *kmsg_dump_reason_str(enum kmsg_dump_reason reason)
4060 case KMSG_DUMP_PANIC:
4062 case KMSG_DUMP_OOPS:
4064 case KMSG_DUMP_EMERG:
4066 case KMSG_DUMP_SHUTDOWN:
4072 EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
4075 * kmsg_dump - dump kernel log to kernel message dumpers.
4076 * @reason: the reason (oops, panic etc) for dumping
4078 * Call each of the registered dumper's dump() callback, which can
4079 * retrieve the kmsg records with kmsg_dump_get_line() or
4080 * kmsg_dump_get_buffer().
4082 void kmsg_dump(enum kmsg_dump_reason reason)
4084 struct kmsg_dumper *dumper;
4087 list_for_each_entry_rcu(dumper, &dump_list, list) {
4088 enum kmsg_dump_reason max_reason = dumper->max_reason;
4091 * If client has not provided a specific max_reason, default
4092 * to KMSG_DUMP_OOPS, unless always_kmsg_dump was set.
4094 if (max_reason == KMSG_DUMP_UNDEF) {
4095 max_reason = always_kmsg_dump ? KMSG_DUMP_MAX :
4098 if (reason > max_reason)
4101 /* invoke dumper which will iterate over records */
4102 dumper->dump(dumper, reason);
4108 * kmsg_dump_get_line - retrieve one kmsg log line
4109 * @iter: kmsg dump iterator
4110 * @syslog: include the "<4>" prefixes
4111 * @line: buffer to copy the line to
4112 * @size: maximum size of the buffer
4113 * @len: length of line placed into buffer
4115 * Start at the beginning of the kmsg buffer, with the oldest kmsg
4116 * record, and copy one record into the provided buffer.
4118 * Consecutive calls will return the next available record moving
4119 * towards the end of the buffer with the youngest messages.
4121 * A return value of FALSE indicates that there are no more records to
4124 bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
4125 char *line, size_t size, size_t *len)
4127 u64 min_seq = latched_seq_read_nolock(&clear_seq);
4128 struct printk_info info;
4129 unsigned int line_count;
4130 struct printk_record r;
4134 if (iter->cur_seq < min_seq)
4135 iter->cur_seq = min_seq;
4137 prb_rec_init_rd(&r, &info, line, size);
4139 /* Read text or count text lines? */
4141 if (!prb_read_valid(prb, iter->cur_seq, &r))
4143 l = record_print_text(&r, syslog, printk_time);
4145 if (!prb_read_valid_info(prb, iter->cur_seq,
4146 &info, &line_count)) {
4149 l = get_record_print_text_size(&info, line_count, syslog,
4154 iter->cur_seq = r.info->seq + 1;
4161 EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
4164 * kmsg_dump_get_buffer - copy kmsg log lines
4165 * @iter: kmsg dump iterator
4166 * @syslog: include the "<4>" prefixes
4167 * @buf: buffer to copy the line to
4168 * @size: maximum size of the buffer
4169 * @len_out: length of line placed into buffer
4171 * Start at the end of the kmsg buffer and fill the provided buffer
4172 * with as many of the *youngest* kmsg records that fit into it.
4173 * If the buffer is large enough, all available kmsg records will be
4174 * copied with a single call.
4176 * Consecutive calls will fill the buffer with the next block of
4177 * available older records, not including the earlier retrieved ones.
4179 * A return value of FALSE indicates that there are no more records to
4182 bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
4183 char *buf, size_t size, size_t *len_out)
4185 u64 min_seq = latched_seq_read_nolock(&clear_seq);
4186 struct printk_info info;
4187 struct printk_record r;
4192 bool time = printk_time;
4197 if (iter->cur_seq < min_seq)
4198 iter->cur_seq = min_seq;
4200 if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
4201 if (info.seq != iter->cur_seq) {
4202 /* messages are gone, move to first available one */
4203 iter->cur_seq = info.seq;
4208 if (iter->cur_seq >= iter->next_seq)
4212 * Find first record that fits, including all following records,
4213 * into the user-provided buffer for this dump. Pass in size-1
4214 * because this function (by way of record_print_text()) will
4215 * not write more than size-1 bytes of text into @buf.
4217 seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,
4218 size - 1, syslog, time);
4221 * Next kmsg_dump_get_buffer() invocation will dump block of
4222 * older records stored right before this one.
4226 prb_rec_init_rd(&r, &info, buf, size);
4228 prb_for_each_record(seq, prb, seq, &r) {
4229 if (r.info->seq >= iter->next_seq)
4232 len += record_print_text(&r, syslog, time);
4234 /* Adjust record to store to remaining buffer space. */
4235 prb_rec_init_rd(&r, &info, buf + len, size - len);
4238 iter->next_seq = next_seq;
4245 EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
4248 * kmsg_dump_rewind - reset the iterator
4249 * @iter: kmsg dump iterator
4251 * Reset the dumper's iterator so that kmsg_dump_get_line() and
4252 * kmsg_dump_get_buffer() can be called again and used multiple
4253 * times within the same dumper.dump() callback.
4255 void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
4257 iter->cur_seq = latched_seq_read_nolock(&clear_seq);
4258 iter->next_seq = prb_next_seq(prb);
4260 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
4265 static atomic_t printk_cpu_sync_owner = ATOMIC_INIT(-1);
4266 static atomic_t printk_cpu_sync_nested = ATOMIC_INIT(0);
4269 * __printk_cpu_sync_wait() - Busy wait until the printk cpu-reentrant
4270 * spinning lock is not owned by any CPU.
4272 * Context: Any context.
4274 void __printk_cpu_sync_wait(void)
4278 } while (atomic_read(&printk_cpu_sync_owner) != -1);
4280 EXPORT_SYMBOL(__printk_cpu_sync_wait);
4283 * __printk_cpu_sync_try_get() - Try to acquire the printk cpu-reentrant
4286 * If no processor has the lock, the calling processor takes the lock and
4287 * becomes the owner. If the calling processor is already the owner of the
4288 * lock, this function succeeds immediately.
4290 * Context: Any context. Expects interrupts to be disabled.
4291 * Return: 1 on success, otherwise 0.
4293 int __printk_cpu_sync_try_get(void)
4298 cpu = smp_processor_id();
4301 * Guarantee loads and stores from this CPU when it is the lock owner
4302 * are _not_ visible to the previous lock owner. This pairs with
4303 * __printk_cpu_sync_put:B.
4305 * Memory barrier involvement:
4307 * If __printk_cpu_sync_try_get:A reads from __printk_cpu_sync_put:B,
4308 * then __printk_cpu_sync_put:A can never read from
4309 * __printk_cpu_sync_try_get:B.
4313 * RELEASE from __printk_cpu_sync_put:A to __printk_cpu_sync_put:B
4314 * of the previous CPU
4316 * ACQUIRE from __printk_cpu_sync_try_get:A to
4317 * __printk_cpu_sync_try_get:B of this CPU
4319 old = atomic_cmpxchg_acquire(&printk_cpu_sync_owner, -1,
4320 cpu); /* LMM(__printk_cpu_sync_try_get:A) */
4323 * This CPU is now the owner and begins loading/storing
4324 * data: LMM(__printk_cpu_sync_try_get:B)
4328 } else if (old == cpu) {
4329 /* This CPU is already the owner. */
4330 atomic_inc(&printk_cpu_sync_nested);
4336 EXPORT_SYMBOL(__printk_cpu_sync_try_get);
4339 * __printk_cpu_sync_put() - Release the printk cpu-reentrant spinning lock.
4341 * The calling processor must be the owner of the lock.
4343 * Context: Any context. Expects interrupts to be disabled.
4345 void __printk_cpu_sync_put(void)
4347 if (atomic_read(&printk_cpu_sync_nested)) {
4348 atomic_dec(&printk_cpu_sync_nested);
4353 * This CPU is finished loading/storing data:
4354 * LMM(__printk_cpu_sync_put:A)
4358 * Guarantee loads and stores from this CPU when it was the
4359 * lock owner are visible to the next lock owner. This pairs
4360 * with __printk_cpu_sync_try_get:A.
4362 * Memory barrier involvement:
4364 * If __printk_cpu_sync_try_get:A reads from __printk_cpu_sync_put:B,
4365 * then __printk_cpu_sync_try_get:B reads from __printk_cpu_sync_put:A.
4369 * RELEASE from __printk_cpu_sync_put:A to __printk_cpu_sync_put:B
4372 * ACQUIRE from __printk_cpu_sync_try_get:A to
4373 * __printk_cpu_sync_try_get:B of the next CPU
4375 atomic_set_release(&printk_cpu_sync_owner,
4376 -1); /* LMM(__printk_cpu_sync_put:B) */
4378 EXPORT_SYMBOL(__printk_cpu_sync_put);
4379 #endif /* CONFIG_SMP */