drm/panthor: Don't add write fences to the shared BOs
[drm/drm-misc.git] / kernel / printk / printk.c
blobbeb808f4c367b9625f43d7d3ecdbd24a55103d2d
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
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).
12 * Ted Ts'o, 2/11/93.
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>
23 #include <linux/mm.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/syscore_ops.h>
38 #include <linux/vmcore_info.h>
39 #include <linux/ratelimit.h>
40 #include <linux/kmsg_dump.h>
41 #include <linux/syslog.h>
42 #include <linux/cpu.h>
43 #include <linux/rculist.h>
44 #include <linux/poll.h>
45 #include <linux/irq_work.h>
46 #include <linux/ctype.h>
47 #include <linux/uio.h>
48 #include <linux/sched/clock.h>
49 #include <linux/sched/debug.h>
50 #include <linux/sched/task_stack.h>
52 #include <linux/uaccess.h>
53 #include <asm/sections.h>
55 #include <trace/events/initcall.h>
56 #define CREATE_TRACE_POINTS
57 #include <trace/events/printk.h>
59 #include "printk_ringbuffer.h"
60 #include "console_cmdline.h"
61 #include "braille.h"
62 #include "internal.h"
64 int console_printk[4] = {
65 CONSOLE_LOGLEVEL_DEFAULT, /* console_loglevel */
66 MESSAGE_LOGLEVEL_DEFAULT, /* default_message_loglevel */
67 CONSOLE_LOGLEVEL_MIN, /* minimum_console_loglevel */
68 CONSOLE_LOGLEVEL_DEFAULT, /* default_console_loglevel */
70 EXPORT_SYMBOL_GPL(console_printk);
72 atomic_t ignore_console_lock_warning __read_mostly = ATOMIC_INIT(0);
73 EXPORT_SYMBOL(ignore_console_lock_warning);
75 EXPORT_TRACEPOINT_SYMBOL_GPL(console);
78 * Low level drivers may need that to know if they can schedule in
79 * their unblank() callback or not. So let's export it.
81 int oops_in_progress;
82 EXPORT_SYMBOL(oops_in_progress);
85 * console_mutex protects console_list updates and console->flags updates.
86 * The flags are synchronized only for consoles that are registered, i.e.
87 * accessible via the console list.
89 static DEFINE_MUTEX(console_mutex);
92 * console_sem protects updates to console->seq
93 * and also provides serialization for console printing.
95 static DEFINE_SEMAPHORE(console_sem, 1);
96 HLIST_HEAD(console_list);
97 EXPORT_SYMBOL_GPL(console_list);
98 DEFINE_STATIC_SRCU(console_srcu);
101 * System may need to suppress printk message under certain
102 * circumstances, like after kernel panic happens.
104 int __read_mostly suppress_printk;
106 #ifdef CONFIG_LOCKDEP
107 static struct lockdep_map console_lock_dep_map = {
108 .name = "console_lock"
111 void lockdep_assert_console_list_lock_held(void)
113 lockdep_assert_held(&console_mutex);
115 EXPORT_SYMBOL(lockdep_assert_console_list_lock_held);
116 #endif
118 #ifdef CONFIG_DEBUG_LOCK_ALLOC
119 bool console_srcu_read_lock_is_held(void)
121 return srcu_read_lock_held(&console_srcu);
123 EXPORT_SYMBOL(console_srcu_read_lock_is_held);
124 #endif
126 enum devkmsg_log_bits {
127 __DEVKMSG_LOG_BIT_ON = 0,
128 __DEVKMSG_LOG_BIT_OFF,
129 __DEVKMSG_LOG_BIT_LOCK,
132 enum devkmsg_log_masks {
133 DEVKMSG_LOG_MASK_ON = BIT(__DEVKMSG_LOG_BIT_ON),
134 DEVKMSG_LOG_MASK_OFF = BIT(__DEVKMSG_LOG_BIT_OFF),
135 DEVKMSG_LOG_MASK_LOCK = BIT(__DEVKMSG_LOG_BIT_LOCK),
138 /* Keep both the 'on' and 'off' bits clear, i.e. ratelimit by default: */
139 #define DEVKMSG_LOG_MASK_DEFAULT 0
141 static unsigned int __read_mostly devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
143 static int __control_devkmsg(char *str)
145 size_t len;
147 if (!str)
148 return -EINVAL;
150 len = str_has_prefix(str, "on");
151 if (len) {
152 devkmsg_log = DEVKMSG_LOG_MASK_ON;
153 return len;
156 len = str_has_prefix(str, "off");
157 if (len) {
158 devkmsg_log = DEVKMSG_LOG_MASK_OFF;
159 return len;
162 len = str_has_prefix(str, "ratelimit");
163 if (len) {
164 devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
165 return len;
168 return -EINVAL;
171 static int __init control_devkmsg(char *str)
173 if (__control_devkmsg(str) < 0) {
174 pr_warn("printk.devkmsg: bad option string '%s'\n", str);
175 return 1;
179 * Set sysctl string accordingly:
181 if (devkmsg_log == DEVKMSG_LOG_MASK_ON)
182 strscpy(devkmsg_log_str, "on");
183 else if (devkmsg_log == DEVKMSG_LOG_MASK_OFF)
184 strscpy(devkmsg_log_str, "off");
185 /* else "ratelimit" which is set by default. */
188 * Sysctl cannot change it anymore. The kernel command line setting of
189 * this parameter is to force the setting to be permanent throughout the
190 * runtime of the system. This is a precation measure against userspace
191 * trying to be a smarta** and attempting to change it up on us.
193 devkmsg_log |= DEVKMSG_LOG_MASK_LOCK;
195 return 1;
197 __setup("printk.devkmsg=", control_devkmsg);
199 char devkmsg_log_str[DEVKMSG_STR_MAX_SIZE] = "ratelimit";
200 #if defined(CONFIG_PRINTK) && defined(CONFIG_SYSCTL)
201 int devkmsg_sysctl_set_loglvl(const struct ctl_table *table, int write,
202 void *buffer, size_t *lenp, loff_t *ppos)
204 char old_str[DEVKMSG_STR_MAX_SIZE];
205 unsigned int old;
206 int err;
208 if (write) {
209 if (devkmsg_log & DEVKMSG_LOG_MASK_LOCK)
210 return -EINVAL;
212 old = devkmsg_log;
213 strscpy(old_str, devkmsg_log_str);
216 err = proc_dostring(table, write, buffer, lenp, ppos);
217 if (err)
218 return err;
220 if (write) {
221 err = __control_devkmsg(devkmsg_log_str);
224 * Do not accept an unknown string OR a known string with
225 * trailing crap...
227 if (err < 0 || (err + 1 != *lenp)) {
229 /* ... and restore old setting. */
230 devkmsg_log = old;
231 strscpy(devkmsg_log_str, old_str);
233 return -EINVAL;
237 return 0;
239 #endif /* CONFIG_PRINTK && CONFIG_SYSCTL */
242 * console_list_lock - Lock the console list
244 * For console list or console->flags updates
246 void console_list_lock(void)
249 * In unregister_console() and console_force_preferred_locked(),
250 * synchronize_srcu() is called with the console_list_lock held.
251 * Therefore it is not allowed that the console_list_lock is taken
252 * with the srcu_lock held.
254 * Detecting if this context is really in the read-side critical
255 * section is only possible if the appropriate debug options are
256 * enabled.
258 WARN_ON_ONCE(debug_lockdep_rcu_enabled() &&
259 srcu_read_lock_held(&console_srcu));
261 mutex_lock(&console_mutex);
263 EXPORT_SYMBOL(console_list_lock);
266 * console_list_unlock - Unlock the console list
268 * Counterpart to console_list_lock()
270 void console_list_unlock(void)
272 mutex_unlock(&console_mutex);
274 EXPORT_SYMBOL(console_list_unlock);
277 * console_srcu_read_lock - Register a new reader for the
278 * SRCU-protected console list
280 * Use for_each_console_srcu() to iterate the console list
282 * Context: Any context.
283 * Return: A cookie to pass to console_srcu_read_unlock().
285 int console_srcu_read_lock(void)
286 __acquires(&console_srcu)
288 return srcu_read_lock_nmisafe(&console_srcu);
290 EXPORT_SYMBOL(console_srcu_read_lock);
293 * console_srcu_read_unlock - Unregister an old reader from
294 * the SRCU-protected console list
295 * @cookie: cookie returned from console_srcu_read_lock()
297 * Counterpart to console_srcu_read_lock()
299 void console_srcu_read_unlock(int cookie)
300 __releases(&console_srcu)
302 srcu_read_unlock_nmisafe(&console_srcu, cookie);
304 EXPORT_SYMBOL(console_srcu_read_unlock);
307 * Helper macros to handle lockdep when locking/unlocking console_sem. We use
308 * macros instead of functions so that _RET_IP_ contains useful information.
310 #define down_console_sem() do { \
311 down(&console_sem);\
312 mutex_acquire(&console_lock_dep_map, 0, 0, _RET_IP_);\
313 } while (0)
315 static int __down_trylock_console_sem(unsigned long ip)
317 int lock_failed;
318 unsigned long flags;
321 * Here and in __up_console_sem() we need to be in safe mode,
322 * because spindump/WARN/etc from under console ->lock will
323 * deadlock in printk()->down_trylock_console_sem() otherwise.
325 printk_safe_enter_irqsave(flags);
326 lock_failed = down_trylock(&console_sem);
327 printk_safe_exit_irqrestore(flags);
329 if (lock_failed)
330 return 1;
331 mutex_acquire(&console_lock_dep_map, 0, 1, ip);
332 return 0;
334 #define down_trylock_console_sem() __down_trylock_console_sem(_RET_IP_)
336 static void __up_console_sem(unsigned long ip)
338 unsigned long flags;
340 mutex_release(&console_lock_dep_map, ip);
342 printk_safe_enter_irqsave(flags);
343 up(&console_sem);
344 printk_safe_exit_irqrestore(flags);
346 #define up_console_sem() __up_console_sem(_RET_IP_)
348 static bool panic_in_progress(void)
350 return unlikely(atomic_read(&panic_cpu) != PANIC_CPU_INVALID);
353 /* Return true if a panic is in progress on the current CPU. */
354 bool this_cpu_in_panic(void)
357 * We can use raw_smp_processor_id() here because it is impossible for
358 * the task to be migrated to the panic_cpu, or away from it. If
359 * panic_cpu has already been set, and we're not currently executing on
360 * that CPU, then we never will be.
362 return unlikely(atomic_read(&panic_cpu) == raw_smp_processor_id());
366 * Return true if a panic is in progress on a remote CPU.
368 * On true, the local CPU should immediately release any printing resources
369 * that may be needed by the panic CPU.
371 bool other_cpu_in_panic(void)
373 return (panic_in_progress() && !this_cpu_in_panic());
377 * This is used for debugging the mess that is the VT code by
378 * keeping track if we have the console semaphore held. It's
379 * definitely not the perfect debug tool (we don't know if _WE_
380 * hold it and are racing, but it helps tracking those weird code
381 * paths in the console code where we end up in places I want
382 * locked without the console semaphore held).
384 static int console_locked;
387 * Array of consoles built from command line options (console=)
390 #define MAX_CMDLINECONSOLES 8
392 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
394 static int preferred_console = -1;
395 int console_set_on_cmdline;
396 EXPORT_SYMBOL(console_set_on_cmdline);
398 /* Flag: console code may call schedule() */
399 static int console_may_schedule;
401 enum con_msg_format_flags {
402 MSG_FORMAT_DEFAULT = 0,
403 MSG_FORMAT_SYSLOG = (1 << 0),
406 static int console_msg_format = MSG_FORMAT_DEFAULT;
409 * The printk log buffer consists of a sequenced collection of records, each
410 * containing variable length message text. Every record also contains its
411 * own meta-data (@info).
413 * Every record meta-data carries the timestamp in microseconds, as well as
414 * the standard userspace syslog level and syslog facility. The usual kernel
415 * messages use LOG_KERN; userspace-injected messages always carry a matching
416 * syslog facility, by default LOG_USER. The origin of every message can be
417 * reliably determined that way.
419 * The human readable log message of a record is available in @text, the
420 * length of the message text in @text_len. The stored message is not
421 * terminated.
423 * Optionally, a record can carry a dictionary of properties (key/value
424 * pairs), to provide userspace with a machine-readable message context.
426 * Examples for well-defined, commonly used property names are:
427 * DEVICE=b12:8 device identifier
428 * b12:8 block dev_t
429 * c127:3 char dev_t
430 * n8 netdev ifindex
431 * +sound:card0 subsystem:devname
432 * SUBSYSTEM=pci driver-core subsystem name
434 * Valid characters in property names are [a-zA-Z0-9.-_]. Property names
435 * and values are terminated by a '\0' character.
437 * Example of record values:
438 * record.text_buf = "it's a line" (unterminated)
439 * record.info.seq = 56
440 * record.info.ts_nsec = 36863
441 * record.info.text_len = 11
442 * record.info.facility = 0 (LOG_KERN)
443 * record.info.flags = 0
444 * record.info.level = 3 (LOG_ERR)
445 * record.info.caller_id = 299 (task 299)
446 * record.info.dev_info.subsystem = "pci" (terminated)
447 * record.info.dev_info.device = "+pci:0000:00:01.0" (terminated)
449 * The 'struct printk_info' buffer must never be directly exported to
450 * userspace, it is a kernel-private implementation detail that might
451 * need to be changed in the future, when the requirements change.
453 * /dev/kmsg exports the structured data in the following line format:
454 * "<level>,<sequnum>,<timestamp>,<contflag>[,additional_values, ... ];<message text>\n"
456 * Users of the export format should ignore possible additional values
457 * separated by ',', and find the message after the ';' character.
459 * The optional key/value pairs are attached as continuation lines starting
460 * with a space character and terminated by a newline. All possible
461 * non-prinatable characters are escaped in the "\xff" notation.
464 /* syslog_lock protects syslog_* variables and write access to clear_seq. */
465 static DEFINE_MUTEX(syslog_lock);
468 * Specifies if a legacy console is registered. If legacy consoles are
469 * present, it is necessary to perform the console lock/unlock dance
470 * whenever console flushing should occur.
472 bool have_legacy_console;
475 * Specifies if an nbcon console is registered. If nbcon consoles are present,
476 * synchronous printing of legacy consoles will not occur during panic until
477 * the backtrace has been stored to the ringbuffer.
479 bool have_nbcon_console;
482 * Specifies if a boot console is registered. If boot consoles are present,
483 * nbcon consoles cannot print simultaneously and must be synchronized by
484 * the console lock. This is because boot consoles and nbcon consoles may
485 * have mapped the same hardware.
487 bool have_boot_console;
489 /* See printk_legacy_allow_panic_sync() for details. */
490 bool legacy_allow_panic_sync;
492 #ifdef CONFIG_PRINTK
493 DECLARE_WAIT_QUEUE_HEAD(log_wait);
494 static DECLARE_WAIT_QUEUE_HEAD(legacy_wait);
495 /* All 3 protected by @syslog_lock. */
496 /* the next printk record to read by syslog(READ) or /proc/kmsg */
497 static u64 syslog_seq;
498 static size_t syslog_partial;
499 static bool syslog_time;
501 /* True when _all_ printer threads are available for printing. */
502 bool printk_kthreads_running;
504 struct latched_seq {
505 seqcount_latch_t latch;
506 u64 val[2];
510 * The next printk record to read after the last 'clear' command. There are
511 * two copies (updated with seqcount_latch) so that reads can locklessly
512 * access a valid value. Writers are synchronized by @syslog_lock.
514 static struct latched_seq clear_seq = {
515 .latch = SEQCNT_LATCH_ZERO(clear_seq.latch),
516 .val[0] = 0,
517 .val[1] = 0,
520 #define LOG_LEVEL(v) ((v) & 0x07)
521 #define LOG_FACILITY(v) ((v) >> 3 & 0xff)
523 /* record buffer */
524 #define LOG_ALIGN __alignof__(unsigned long)
525 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
526 #define LOG_BUF_LEN_MAX (u32)(1 << 31)
527 static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
528 static char *log_buf = __log_buf;
529 static u32 log_buf_len = __LOG_BUF_LEN;
532 * Define the average message size. This only affects the number of
533 * descriptors that will be available. Underestimating is better than
534 * overestimating (too many available descriptors is better than not enough).
536 #define PRB_AVGBITS 5 /* 32 character average length */
538 #if CONFIG_LOG_BUF_SHIFT <= PRB_AVGBITS
539 #error CONFIG_LOG_BUF_SHIFT value too small.
540 #endif
541 _DEFINE_PRINTKRB(printk_rb_static, CONFIG_LOG_BUF_SHIFT - PRB_AVGBITS,
542 PRB_AVGBITS, &__log_buf[0]);
544 static struct printk_ringbuffer printk_rb_dynamic;
546 struct printk_ringbuffer *prb = &printk_rb_static;
549 * We cannot access per-CPU data (e.g. per-CPU flush irq_work) before
550 * per_cpu_areas are initialised. This variable is set to true when
551 * it's safe to access per-CPU data.
553 static bool __printk_percpu_data_ready __ro_after_init;
555 bool printk_percpu_data_ready(void)
557 return __printk_percpu_data_ready;
560 /* Must be called under syslog_lock. */
561 static void latched_seq_write(struct latched_seq *ls, u64 val)
563 raw_write_seqcount_latch(&ls->latch);
564 ls->val[0] = val;
565 raw_write_seqcount_latch(&ls->latch);
566 ls->val[1] = val;
569 /* Can be called from any context. */
570 static u64 latched_seq_read_nolock(struct latched_seq *ls)
572 unsigned int seq;
573 unsigned int idx;
574 u64 val;
576 do {
577 seq = raw_read_seqcount_latch(&ls->latch);
578 idx = seq & 0x1;
579 val = ls->val[idx];
580 } while (raw_read_seqcount_latch_retry(&ls->latch, seq));
582 return val;
585 /* Return log buffer address */
586 char *log_buf_addr_get(void)
588 return log_buf;
591 /* Return log buffer size */
592 u32 log_buf_len_get(void)
594 return log_buf_len;
598 * Define how much of the log buffer we could take at maximum. The value
599 * must be greater than two. Note that only half of the buffer is available
600 * when the index points to the middle.
602 #define MAX_LOG_TAKE_PART 4
603 static const char trunc_msg[] = "<truncated>";
605 static void truncate_msg(u16 *text_len, u16 *trunc_msg_len)
608 * The message should not take the whole buffer. Otherwise, it might
609 * get removed too soon.
611 u32 max_text_len = log_buf_len / MAX_LOG_TAKE_PART;
613 if (*text_len > max_text_len)
614 *text_len = max_text_len;
616 /* enable the warning message (if there is room) */
617 *trunc_msg_len = strlen(trunc_msg);
618 if (*text_len >= *trunc_msg_len)
619 *text_len -= *trunc_msg_len;
620 else
621 *trunc_msg_len = 0;
624 int dmesg_restrict = IS_ENABLED(CONFIG_SECURITY_DMESG_RESTRICT);
626 static int syslog_action_restricted(int type)
628 if (dmesg_restrict)
629 return 1;
631 * Unless restricted, we allow "read all" and "get buffer size"
632 * for everybody.
634 return type != SYSLOG_ACTION_READ_ALL &&
635 type != SYSLOG_ACTION_SIZE_BUFFER;
638 static int check_syslog_permissions(int type, int source)
641 * If this is from /proc/kmsg and we've already opened it, then we've
642 * already done the capabilities checks at open time.
644 if (source == SYSLOG_FROM_PROC && type != SYSLOG_ACTION_OPEN)
645 goto ok;
647 if (syslog_action_restricted(type)) {
648 if (capable(CAP_SYSLOG))
649 goto ok;
650 return -EPERM;
653 return security_syslog(type);
656 static void append_char(char **pp, char *e, char c)
658 if (*pp < e)
659 *(*pp)++ = c;
662 static ssize_t info_print_ext_header(char *buf, size_t size,
663 struct printk_info *info)
665 u64 ts_usec = info->ts_nsec;
666 char caller[20];
667 #ifdef CONFIG_PRINTK_CALLER
668 u32 id = info->caller_id;
670 snprintf(caller, sizeof(caller), ",caller=%c%u",
671 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
672 #else
673 caller[0] = '\0';
674 #endif
676 do_div(ts_usec, 1000);
678 return scnprintf(buf, size, "%u,%llu,%llu,%c%s;",
679 (info->facility << 3) | info->level, info->seq,
680 ts_usec, info->flags & LOG_CONT ? 'c' : '-', caller);
683 static ssize_t msg_add_ext_text(char *buf, size_t size,
684 const char *text, size_t text_len,
685 unsigned char endc)
687 char *p = buf, *e = buf + size;
688 size_t i;
690 /* escape non-printable characters */
691 for (i = 0; i < text_len; i++) {
692 unsigned char c = text[i];
694 if (c < ' ' || c >= 127 || c == '\\')
695 p += scnprintf(p, e - p, "\\x%02x", c);
696 else
697 append_char(&p, e, c);
699 append_char(&p, e, endc);
701 return p - buf;
704 static ssize_t msg_add_dict_text(char *buf, size_t size,
705 const char *key, const char *val)
707 size_t val_len = strlen(val);
708 ssize_t len;
710 if (!val_len)
711 return 0;
713 len = msg_add_ext_text(buf, size, "", 0, ' '); /* dict prefix */
714 len += msg_add_ext_text(buf + len, size - len, key, strlen(key), '=');
715 len += msg_add_ext_text(buf + len, size - len, val, val_len, '\n');
717 return len;
720 static ssize_t msg_print_ext_body(char *buf, size_t size,
721 char *text, size_t text_len,
722 struct dev_printk_info *dev_info)
724 ssize_t len;
726 len = msg_add_ext_text(buf, size, text, text_len, '\n');
728 if (!dev_info)
729 goto out;
731 len += msg_add_dict_text(buf + len, size - len, "SUBSYSTEM",
732 dev_info->subsystem);
733 len += msg_add_dict_text(buf + len, size - len, "DEVICE",
734 dev_info->device);
735 out:
736 return len;
739 /* /dev/kmsg - userspace message inject/listen interface */
740 struct devkmsg_user {
741 atomic64_t seq;
742 struct ratelimit_state rs;
743 struct mutex lock;
744 struct printk_buffers pbufs;
747 static __printf(3, 4) __cold
748 int devkmsg_emit(int facility, int level, const char *fmt, ...)
750 va_list args;
751 int r;
753 va_start(args, fmt);
754 r = vprintk_emit(facility, level, NULL, fmt, args);
755 va_end(args);
757 return r;
760 static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
762 char *buf, *line;
763 int level = default_message_loglevel;
764 int facility = 1; /* LOG_USER */
765 struct file *file = iocb->ki_filp;
766 struct devkmsg_user *user = file->private_data;
767 size_t len = iov_iter_count(from);
768 ssize_t ret = len;
770 if (len > PRINTKRB_RECORD_MAX)
771 return -EINVAL;
773 /* Ignore when user logging is disabled. */
774 if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
775 return len;
777 /* Ratelimit when not explicitly enabled. */
778 if (!(devkmsg_log & DEVKMSG_LOG_MASK_ON)) {
779 if (!___ratelimit(&user->rs, current->comm))
780 return ret;
783 buf = kmalloc(len+1, GFP_KERNEL);
784 if (buf == NULL)
785 return -ENOMEM;
787 buf[len] = '\0';
788 if (!copy_from_iter_full(buf, len, from)) {
789 kfree(buf);
790 return -EFAULT;
794 * Extract and skip the syslog prefix <[0-9]*>. Coming from userspace
795 * the decimal value represents 32bit, the lower 3 bit are the log
796 * level, the rest are the log facility.
798 * If no prefix or no userspace facility is specified, we
799 * enforce LOG_USER, to be able to reliably distinguish
800 * kernel-generated messages from userspace-injected ones.
802 line = buf;
803 if (line[0] == '<') {
804 char *endp = NULL;
805 unsigned int u;
807 u = simple_strtoul(line + 1, &endp, 10);
808 if (endp && endp[0] == '>') {
809 level = LOG_LEVEL(u);
810 if (LOG_FACILITY(u) != 0)
811 facility = LOG_FACILITY(u);
812 endp++;
813 line = endp;
817 devkmsg_emit(facility, level, "%s", line);
818 kfree(buf);
819 return ret;
822 static ssize_t devkmsg_read(struct file *file, char __user *buf,
823 size_t count, loff_t *ppos)
825 struct devkmsg_user *user = file->private_data;
826 char *outbuf = &user->pbufs.outbuf[0];
827 struct printk_message pmsg = {
828 .pbufs = &user->pbufs,
830 ssize_t ret;
832 ret = mutex_lock_interruptible(&user->lock);
833 if (ret)
834 return ret;
836 if (!printk_get_next_message(&pmsg, atomic64_read(&user->seq), true, false)) {
837 if (file->f_flags & O_NONBLOCK) {
838 ret = -EAGAIN;
839 goto out;
843 * Guarantee this task is visible on the waitqueue before
844 * checking the wake condition.
846 * The full memory barrier within set_current_state() of
847 * prepare_to_wait_event() pairs with the full memory barrier
848 * within wq_has_sleeper().
850 * This pairs with __wake_up_klogd:A.
852 ret = wait_event_interruptible(log_wait,
853 printk_get_next_message(&pmsg, atomic64_read(&user->seq), true,
854 false)); /* LMM(devkmsg_read:A) */
855 if (ret)
856 goto out;
859 if (pmsg.dropped) {
860 /* our last seen message is gone, return error and reset */
861 atomic64_set(&user->seq, pmsg.seq);
862 ret = -EPIPE;
863 goto out;
866 atomic64_set(&user->seq, pmsg.seq + 1);
868 if (pmsg.outbuf_len > count) {
869 ret = -EINVAL;
870 goto out;
873 if (copy_to_user(buf, outbuf, pmsg.outbuf_len)) {
874 ret = -EFAULT;
875 goto out;
877 ret = pmsg.outbuf_len;
878 out:
879 mutex_unlock(&user->lock);
880 return ret;
884 * Be careful when modifying this function!!!
886 * Only few operations are supported because the device works only with the
887 * entire variable length messages (records). Non-standard values are
888 * returned in the other cases and has been this way for quite some time.
889 * User space applications might depend on this behavior.
891 static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
893 struct devkmsg_user *user = file->private_data;
894 loff_t ret = 0;
896 if (offset)
897 return -ESPIPE;
899 switch (whence) {
900 case SEEK_SET:
901 /* the first record */
902 atomic64_set(&user->seq, prb_first_valid_seq(prb));
903 break;
904 case SEEK_DATA:
906 * The first record after the last SYSLOG_ACTION_CLEAR,
907 * like issued by 'dmesg -c'. Reading /dev/kmsg itself
908 * changes no global state, and does not clear anything.
910 atomic64_set(&user->seq, latched_seq_read_nolock(&clear_seq));
911 break;
912 case SEEK_END:
913 /* after the last record */
914 atomic64_set(&user->seq, prb_next_seq(prb));
915 break;
916 default:
917 ret = -EINVAL;
919 return ret;
922 static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
924 struct devkmsg_user *user = file->private_data;
925 struct printk_info info;
926 __poll_t ret = 0;
928 poll_wait(file, &log_wait, wait);
930 if (prb_read_valid_info(prb, atomic64_read(&user->seq), &info, NULL)) {
931 /* return error when data has vanished underneath us */
932 if (info.seq != atomic64_read(&user->seq))
933 ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;
934 else
935 ret = EPOLLIN|EPOLLRDNORM;
938 return ret;
941 static int devkmsg_open(struct inode *inode, struct file *file)
943 struct devkmsg_user *user;
944 int err;
946 if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
947 return -EPERM;
949 /* write-only does not need any file context */
950 if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
951 err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
952 SYSLOG_FROM_READER);
953 if (err)
954 return err;
957 user = kvmalloc(sizeof(struct devkmsg_user), GFP_KERNEL);
958 if (!user)
959 return -ENOMEM;
961 ratelimit_default_init(&user->rs);
962 ratelimit_set_flags(&user->rs, RATELIMIT_MSG_ON_RELEASE);
964 mutex_init(&user->lock);
966 atomic64_set(&user->seq, prb_first_valid_seq(prb));
968 file->private_data = user;
969 return 0;
972 static int devkmsg_release(struct inode *inode, struct file *file)
974 struct devkmsg_user *user = file->private_data;
976 ratelimit_state_exit(&user->rs);
978 mutex_destroy(&user->lock);
979 kvfree(user);
980 return 0;
983 const struct file_operations kmsg_fops = {
984 .open = devkmsg_open,
985 .read = devkmsg_read,
986 .write_iter = devkmsg_write,
987 .llseek = devkmsg_llseek,
988 .poll = devkmsg_poll,
989 .release = devkmsg_release,
992 #ifdef CONFIG_VMCORE_INFO
994 * This appends the listed symbols to /proc/vmcore
996 * /proc/vmcore is used by various utilities, like crash and makedumpfile to
997 * obtain access to symbols that are otherwise very difficult to locate. These
998 * symbols are specifically used so that utilities can access and extract the
999 * dmesg log from a vmcore file after a crash.
1001 void log_buf_vmcoreinfo_setup(void)
1003 struct dev_printk_info *dev_info = NULL;
1005 VMCOREINFO_SYMBOL(prb);
1006 VMCOREINFO_SYMBOL(printk_rb_static);
1007 VMCOREINFO_SYMBOL(clear_seq);
1010 * Export struct size and field offsets. User space tools can
1011 * parse it and detect any changes to structure down the line.
1014 VMCOREINFO_STRUCT_SIZE(printk_ringbuffer);
1015 VMCOREINFO_OFFSET(printk_ringbuffer, desc_ring);
1016 VMCOREINFO_OFFSET(printk_ringbuffer, text_data_ring);
1017 VMCOREINFO_OFFSET(printk_ringbuffer, fail);
1019 VMCOREINFO_STRUCT_SIZE(prb_desc_ring);
1020 VMCOREINFO_OFFSET(prb_desc_ring, count_bits);
1021 VMCOREINFO_OFFSET(prb_desc_ring, descs);
1022 VMCOREINFO_OFFSET(prb_desc_ring, infos);
1023 VMCOREINFO_OFFSET(prb_desc_ring, head_id);
1024 VMCOREINFO_OFFSET(prb_desc_ring, tail_id);
1026 VMCOREINFO_STRUCT_SIZE(prb_desc);
1027 VMCOREINFO_OFFSET(prb_desc, state_var);
1028 VMCOREINFO_OFFSET(prb_desc, text_blk_lpos);
1030 VMCOREINFO_STRUCT_SIZE(prb_data_blk_lpos);
1031 VMCOREINFO_OFFSET(prb_data_blk_lpos, begin);
1032 VMCOREINFO_OFFSET(prb_data_blk_lpos, next);
1034 VMCOREINFO_STRUCT_SIZE(printk_info);
1035 VMCOREINFO_OFFSET(printk_info, seq);
1036 VMCOREINFO_OFFSET(printk_info, ts_nsec);
1037 VMCOREINFO_OFFSET(printk_info, text_len);
1038 VMCOREINFO_OFFSET(printk_info, caller_id);
1039 VMCOREINFO_OFFSET(printk_info, dev_info);
1041 VMCOREINFO_STRUCT_SIZE(dev_printk_info);
1042 VMCOREINFO_OFFSET(dev_printk_info, subsystem);
1043 VMCOREINFO_LENGTH(printk_info_subsystem, sizeof(dev_info->subsystem));
1044 VMCOREINFO_OFFSET(dev_printk_info, device);
1045 VMCOREINFO_LENGTH(printk_info_device, sizeof(dev_info->device));
1047 VMCOREINFO_STRUCT_SIZE(prb_data_ring);
1048 VMCOREINFO_OFFSET(prb_data_ring, size_bits);
1049 VMCOREINFO_OFFSET(prb_data_ring, data);
1050 VMCOREINFO_OFFSET(prb_data_ring, head_lpos);
1051 VMCOREINFO_OFFSET(prb_data_ring, tail_lpos);
1053 VMCOREINFO_SIZE(atomic_long_t);
1054 VMCOREINFO_TYPE_OFFSET(atomic_long_t, counter);
1056 VMCOREINFO_STRUCT_SIZE(latched_seq);
1057 VMCOREINFO_OFFSET(latched_seq, val);
1059 #endif
1061 /* requested log_buf_len from kernel cmdline */
1062 static unsigned long __initdata new_log_buf_len;
1064 /* we practice scaling the ring buffer by powers of 2 */
1065 static void __init log_buf_len_update(u64 size)
1067 if (size > (u64)LOG_BUF_LEN_MAX) {
1068 size = (u64)LOG_BUF_LEN_MAX;
1069 pr_err("log_buf over 2G is not supported.\n");
1072 if (size)
1073 size = roundup_pow_of_two(size);
1074 if (size > log_buf_len)
1075 new_log_buf_len = (unsigned long)size;
1078 /* save requested log_buf_len since it's too early to process it */
1079 static int __init log_buf_len_setup(char *str)
1081 u64 size;
1083 if (!str)
1084 return -EINVAL;
1086 size = memparse(str, &str);
1088 log_buf_len_update(size);
1090 return 0;
1092 early_param("log_buf_len", log_buf_len_setup);
1094 #ifdef CONFIG_SMP
1095 #define __LOG_CPU_MAX_BUF_LEN (1 << CONFIG_LOG_CPU_MAX_BUF_SHIFT)
1097 static void __init log_buf_add_cpu(void)
1099 unsigned int cpu_extra;
1102 * archs should set up cpu_possible_bits properly with
1103 * set_cpu_possible() after setup_arch() but just in
1104 * case lets ensure this is valid.
1106 if (num_possible_cpus() == 1)
1107 return;
1109 cpu_extra = (num_possible_cpus() - 1) * __LOG_CPU_MAX_BUF_LEN;
1111 /* by default this will only continue through for large > 64 CPUs */
1112 if (cpu_extra <= __LOG_BUF_LEN / 2)
1113 return;
1115 pr_info("log_buf_len individual max cpu contribution: %d bytes\n",
1116 __LOG_CPU_MAX_BUF_LEN);
1117 pr_info("log_buf_len total cpu_extra contributions: %d bytes\n",
1118 cpu_extra);
1119 pr_info("log_buf_len min size: %d bytes\n", __LOG_BUF_LEN);
1121 log_buf_len_update(cpu_extra + __LOG_BUF_LEN);
1123 #else /* !CONFIG_SMP */
1124 static inline void log_buf_add_cpu(void) {}
1125 #endif /* CONFIG_SMP */
1127 static void __init set_percpu_data_ready(void)
1129 __printk_percpu_data_ready = true;
1132 static unsigned int __init add_to_rb(struct printk_ringbuffer *rb,
1133 struct printk_record *r)
1135 struct prb_reserved_entry e;
1136 struct printk_record dest_r;
1138 prb_rec_init_wr(&dest_r, r->info->text_len);
1140 if (!prb_reserve(&e, rb, &dest_r))
1141 return 0;
1143 memcpy(&dest_r.text_buf[0], &r->text_buf[0], r->info->text_len);
1144 dest_r.info->text_len = r->info->text_len;
1145 dest_r.info->facility = r->info->facility;
1146 dest_r.info->level = r->info->level;
1147 dest_r.info->flags = r->info->flags;
1148 dest_r.info->ts_nsec = r->info->ts_nsec;
1149 dest_r.info->caller_id = r->info->caller_id;
1150 memcpy(&dest_r.info->dev_info, &r->info->dev_info, sizeof(dest_r.info->dev_info));
1152 prb_final_commit(&e);
1154 return prb_record_text_space(&e);
1157 static char setup_text_buf[PRINTKRB_RECORD_MAX] __initdata;
1159 void __init setup_log_buf(int early)
1161 struct printk_info *new_infos;
1162 unsigned int new_descs_count;
1163 struct prb_desc *new_descs;
1164 struct printk_info info;
1165 struct printk_record r;
1166 unsigned int text_size;
1167 size_t new_descs_size;
1168 size_t new_infos_size;
1169 unsigned long flags;
1170 char *new_log_buf;
1171 unsigned int free;
1172 u64 seq;
1175 * Some archs call setup_log_buf() multiple times - first is very
1176 * early, e.g. from setup_arch(), and second - when percpu_areas
1177 * are initialised.
1179 if (!early)
1180 set_percpu_data_ready();
1182 if (log_buf != __log_buf)
1183 return;
1185 if (!early && !new_log_buf_len)
1186 log_buf_add_cpu();
1188 if (!new_log_buf_len)
1189 return;
1191 new_descs_count = new_log_buf_len >> PRB_AVGBITS;
1192 if (new_descs_count == 0) {
1193 pr_err("new_log_buf_len: %lu too small\n", new_log_buf_len);
1194 return;
1197 new_log_buf = memblock_alloc(new_log_buf_len, LOG_ALIGN);
1198 if (unlikely(!new_log_buf)) {
1199 pr_err("log_buf_len: %lu text bytes not available\n",
1200 new_log_buf_len);
1201 return;
1204 new_descs_size = new_descs_count * sizeof(struct prb_desc);
1205 new_descs = memblock_alloc(new_descs_size, LOG_ALIGN);
1206 if (unlikely(!new_descs)) {
1207 pr_err("log_buf_len: %zu desc bytes not available\n",
1208 new_descs_size);
1209 goto err_free_log_buf;
1212 new_infos_size = new_descs_count * sizeof(struct printk_info);
1213 new_infos = memblock_alloc(new_infos_size, LOG_ALIGN);
1214 if (unlikely(!new_infos)) {
1215 pr_err("log_buf_len: %zu info bytes not available\n",
1216 new_infos_size);
1217 goto err_free_descs;
1220 prb_rec_init_rd(&r, &info, &setup_text_buf[0], sizeof(setup_text_buf));
1222 prb_init(&printk_rb_dynamic,
1223 new_log_buf, ilog2(new_log_buf_len),
1224 new_descs, ilog2(new_descs_count),
1225 new_infos);
1227 local_irq_save(flags);
1229 log_buf_len = new_log_buf_len;
1230 log_buf = new_log_buf;
1231 new_log_buf_len = 0;
1233 free = __LOG_BUF_LEN;
1234 prb_for_each_record(0, &printk_rb_static, seq, &r) {
1235 text_size = add_to_rb(&printk_rb_dynamic, &r);
1236 if (text_size > free)
1237 free = 0;
1238 else
1239 free -= text_size;
1242 prb = &printk_rb_dynamic;
1244 local_irq_restore(flags);
1247 * Copy any remaining messages that might have appeared from
1248 * NMI context after copying but before switching to the
1249 * dynamic buffer.
1251 prb_for_each_record(seq, &printk_rb_static, seq, &r) {
1252 text_size = add_to_rb(&printk_rb_dynamic, &r);
1253 if (text_size > free)
1254 free = 0;
1255 else
1256 free -= text_size;
1259 if (seq != prb_next_seq(&printk_rb_static)) {
1260 pr_err("dropped %llu messages\n",
1261 prb_next_seq(&printk_rb_static) - seq);
1264 pr_info("log_buf_len: %u bytes\n", log_buf_len);
1265 pr_info("early log buf free: %u(%u%%)\n",
1266 free, (free * 100) / __LOG_BUF_LEN);
1267 return;
1269 err_free_descs:
1270 memblock_free(new_descs, new_descs_size);
1271 err_free_log_buf:
1272 memblock_free(new_log_buf, new_log_buf_len);
1275 static bool __read_mostly ignore_loglevel;
1277 static int __init ignore_loglevel_setup(char *str)
1279 ignore_loglevel = true;
1280 pr_info("debug: ignoring loglevel setting.\n");
1282 return 0;
1285 early_param("ignore_loglevel", ignore_loglevel_setup);
1286 module_param(ignore_loglevel, bool, S_IRUGO | S_IWUSR);
1287 MODULE_PARM_DESC(ignore_loglevel,
1288 "ignore loglevel setting (prints all kernel messages to the console)");
1290 static bool suppress_message_printing(int level)
1292 return (level >= console_loglevel && !ignore_loglevel);
1295 #ifdef CONFIG_BOOT_PRINTK_DELAY
1297 static int boot_delay; /* msecs delay after each printk during bootup */
1298 static unsigned long long loops_per_msec; /* based on boot_delay */
1300 static int __init boot_delay_setup(char *str)
1302 unsigned long lpj;
1304 lpj = preset_lpj ? preset_lpj : 1000000; /* some guess */
1305 loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
1307 get_option(&str, &boot_delay);
1308 if (boot_delay > 10 * 1000)
1309 boot_delay = 0;
1311 pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
1312 "HZ: %d, loops_per_msec: %llu\n",
1313 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
1314 return 0;
1316 early_param("boot_delay", boot_delay_setup);
1318 static void boot_delay_msec(int level)
1320 unsigned long long k;
1321 unsigned long timeout;
1323 if ((boot_delay == 0 || system_state >= SYSTEM_RUNNING)
1324 || suppress_message_printing(level)) {
1325 return;
1328 k = (unsigned long long)loops_per_msec * boot_delay;
1330 timeout = jiffies + msecs_to_jiffies(boot_delay);
1331 while (k) {
1332 k--;
1333 cpu_relax();
1335 * use (volatile) jiffies to prevent
1336 * compiler reduction; loop termination via jiffies
1337 * is secondary and may or may not happen.
1339 if (time_after(jiffies, timeout))
1340 break;
1341 touch_nmi_watchdog();
1344 #else
1345 static inline void boot_delay_msec(int level)
1348 #endif
1350 static bool printk_time = IS_ENABLED(CONFIG_PRINTK_TIME);
1351 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
1353 static size_t print_syslog(unsigned int level, char *buf)
1355 return sprintf(buf, "<%u>", level);
1358 static size_t print_time(u64 ts, char *buf)
1360 unsigned long rem_nsec = do_div(ts, 1000000000);
1362 return sprintf(buf, "[%5lu.%06lu]",
1363 (unsigned long)ts, rem_nsec / 1000);
1366 #ifdef CONFIG_PRINTK_CALLER
1367 static size_t print_caller(u32 id, char *buf)
1369 char caller[12];
1371 snprintf(caller, sizeof(caller), "%c%u",
1372 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
1373 return sprintf(buf, "[%6s]", caller);
1375 #else
1376 #define print_caller(id, buf) 0
1377 #endif
1379 static size_t info_print_prefix(const struct printk_info *info, bool syslog,
1380 bool time, char *buf)
1382 size_t len = 0;
1384 if (syslog)
1385 len = print_syslog((info->facility << 3) | info->level, buf);
1387 if (time)
1388 len += print_time(info->ts_nsec, buf + len);
1390 len += print_caller(info->caller_id, buf + len);
1392 if (IS_ENABLED(CONFIG_PRINTK_CALLER) || time) {
1393 buf[len++] = ' ';
1394 buf[len] = '\0';
1397 return len;
1401 * Prepare the record for printing. The text is shifted within the given
1402 * buffer to avoid a need for another one. The following operations are
1403 * done:
1405 * - Add prefix for each line.
1406 * - Drop truncated lines that no longer fit into the buffer.
1407 * - Add the trailing newline that has been removed in vprintk_store().
1408 * - Add a string terminator.
1410 * Since the produced string is always terminated, the maximum possible
1411 * return value is @r->text_buf_size - 1;
1413 * Return: The length of the updated/prepared text, including the added
1414 * prefixes and the newline. The terminator is not counted. The dropped
1415 * line(s) are not counted.
1417 static size_t record_print_text(struct printk_record *r, bool syslog,
1418 bool time)
1420 size_t text_len = r->info->text_len;
1421 size_t buf_size = r->text_buf_size;
1422 char *text = r->text_buf;
1423 char prefix[PRINTK_PREFIX_MAX];
1424 bool truncated = false;
1425 size_t prefix_len;
1426 size_t line_len;
1427 size_t len = 0;
1428 char *next;
1431 * If the message was truncated because the buffer was not large
1432 * enough, treat the available text as if it were the full text.
1434 if (text_len > buf_size)
1435 text_len = buf_size;
1437 prefix_len = info_print_prefix(r->info, syslog, time, prefix);
1440 * @text_len: bytes of unprocessed text
1441 * @line_len: bytes of current line _without_ newline
1442 * @text: pointer to beginning of current line
1443 * @len: number of bytes prepared in r->text_buf
1445 for (;;) {
1446 next = memchr(text, '\n', text_len);
1447 if (next) {
1448 line_len = next - text;
1449 } else {
1450 /* Drop truncated line(s). */
1451 if (truncated)
1452 break;
1453 line_len = text_len;
1457 * Truncate the text if there is not enough space to add the
1458 * prefix and a trailing newline and a terminator.
1460 if (len + prefix_len + text_len + 1 + 1 > buf_size) {
1461 /* Drop even the current line if no space. */
1462 if (len + prefix_len + line_len + 1 + 1 > buf_size)
1463 break;
1465 text_len = buf_size - len - prefix_len - 1 - 1;
1466 truncated = true;
1469 memmove(text + prefix_len, text, text_len);
1470 memcpy(text, prefix, prefix_len);
1473 * Increment the prepared length to include the text and
1474 * prefix that were just moved+copied. Also increment for the
1475 * newline at the end of this line. If this is the last line,
1476 * there is no newline, but it will be added immediately below.
1478 len += prefix_len + line_len + 1;
1479 if (text_len == line_len) {
1481 * This is the last line. Add the trailing newline
1482 * removed in vprintk_store().
1484 text[prefix_len + line_len] = '\n';
1485 break;
1489 * Advance beyond the added prefix and the related line with
1490 * its newline.
1492 text += prefix_len + line_len + 1;
1495 * The remaining text has only decreased by the line with its
1496 * newline.
1498 * Note that @text_len can become zero. It happens when @text
1499 * ended with a newline (either due to truncation or the
1500 * original string ending with "\n\n"). The loop is correctly
1501 * repeated and (if not truncated) an empty line with a prefix
1502 * will be prepared.
1504 text_len -= line_len + 1;
1508 * If a buffer was provided, it will be terminated. Space for the
1509 * string terminator is guaranteed to be available. The terminator is
1510 * not counted in the return value.
1512 if (buf_size > 0)
1513 r->text_buf[len] = 0;
1515 return len;
1518 static size_t get_record_print_text_size(struct printk_info *info,
1519 unsigned int line_count,
1520 bool syslog, bool time)
1522 char prefix[PRINTK_PREFIX_MAX];
1523 size_t prefix_len;
1525 prefix_len = info_print_prefix(info, syslog, time, prefix);
1528 * Each line will be preceded with a prefix. The intermediate
1529 * newlines are already within the text, but a final trailing
1530 * newline will be added.
1532 return ((prefix_len * line_count) + info->text_len + 1);
1536 * Beginning with @start_seq, find the first record where it and all following
1537 * records up to (but not including) @max_seq fit into @size.
1539 * @max_seq is simply an upper bound and does not need to exist. If the caller
1540 * does not require an upper bound, -1 can be used for @max_seq.
1542 static u64 find_first_fitting_seq(u64 start_seq, u64 max_seq, size_t size,
1543 bool syslog, bool time)
1545 struct printk_info info;
1546 unsigned int line_count;
1547 size_t len = 0;
1548 u64 seq;
1550 /* Determine the size of the records up to @max_seq. */
1551 prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
1552 if (info.seq >= max_seq)
1553 break;
1554 len += get_record_print_text_size(&info, line_count, syslog, time);
1558 * Adjust the upper bound for the next loop to avoid subtracting
1559 * lengths that were never added.
1561 if (seq < max_seq)
1562 max_seq = seq;
1565 * Move first record forward until length fits into the buffer. Ignore
1566 * newest messages that were not counted in the above cycle. Messages
1567 * might appear and get lost in the meantime. This is a best effort
1568 * that prevents an infinite loop that could occur with a retry.
1570 prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
1571 if (len <= size || info.seq >= max_seq)
1572 break;
1573 len -= get_record_print_text_size(&info, line_count, syslog, time);
1576 return seq;
1579 /* The caller is responsible for making sure @size is greater than 0. */
1580 static int syslog_print(char __user *buf, int size)
1582 struct printk_info info;
1583 struct printk_record r;
1584 char *text;
1585 int len = 0;
1586 u64 seq;
1588 text = kmalloc(PRINTK_MESSAGE_MAX, GFP_KERNEL);
1589 if (!text)
1590 return -ENOMEM;
1592 prb_rec_init_rd(&r, &info, text, PRINTK_MESSAGE_MAX);
1594 mutex_lock(&syslog_lock);
1597 * Wait for the @syslog_seq record to be available. @syslog_seq may
1598 * change while waiting.
1600 do {
1601 seq = syslog_seq;
1603 mutex_unlock(&syslog_lock);
1605 * Guarantee this task is visible on the waitqueue before
1606 * checking the wake condition.
1608 * The full memory barrier within set_current_state() of
1609 * prepare_to_wait_event() pairs with the full memory barrier
1610 * within wq_has_sleeper().
1612 * This pairs with __wake_up_klogd:A.
1614 len = wait_event_interruptible(log_wait,
1615 prb_read_valid(prb, seq, NULL)); /* LMM(syslog_print:A) */
1616 mutex_lock(&syslog_lock);
1618 if (len)
1619 goto out;
1620 } while (syslog_seq != seq);
1623 * Copy records that fit into the buffer. The above cycle makes sure
1624 * that the first record is always available.
1626 do {
1627 size_t n;
1628 size_t skip;
1629 int err;
1631 if (!prb_read_valid(prb, syslog_seq, &r))
1632 break;
1634 if (r.info->seq != syslog_seq) {
1635 /* message is gone, move to next valid one */
1636 syslog_seq = r.info->seq;
1637 syslog_partial = 0;
1641 * To keep reading/counting partial line consistent,
1642 * use printk_time value as of the beginning of a line.
1644 if (!syslog_partial)
1645 syslog_time = printk_time;
1647 skip = syslog_partial;
1648 n = record_print_text(&r, true, syslog_time);
1649 if (n - syslog_partial <= size) {
1650 /* message fits into buffer, move forward */
1651 syslog_seq = r.info->seq + 1;
1652 n -= syslog_partial;
1653 syslog_partial = 0;
1654 } else if (!len){
1655 /* partial read(), remember position */
1656 n = size;
1657 syslog_partial += n;
1658 } else
1659 n = 0;
1661 if (!n)
1662 break;
1664 mutex_unlock(&syslog_lock);
1665 err = copy_to_user(buf, text + skip, n);
1666 mutex_lock(&syslog_lock);
1668 if (err) {
1669 if (!len)
1670 len = -EFAULT;
1671 break;
1674 len += n;
1675 size -= n;
1676 buf += n;
1677 } while (size);
1678 out:
1679 mutex_unlock(&syslog_lock);
1680 kfree(text);
1681 return len;
1684 static int syslog_print_all(char __user *buf, int size, bool clear)
1686 struct printk_info info;
1687 struct printk_record r;
1688 char *text;
1689 int len = 0;
1690 u64 seq;
1691 bool time;
1693 text = kmalloc(PRINTK_MESSAGE_MAX, GFP_KERNEL);
1694 if (!text)
1695 return -ENOMEM;
1697 time = printk_time;
1699 * Find first record that fits, including all following records,
1700 * into the user-provided buffer for this dump.
1702 seq = find_first_fitting_seq(latched_seq_read_nolock(&clear_seq), -1,
1703 size, true, time);
1705 prb_rec_init_rd(&r, &info, text, PRINTK_MESSAGE_MAX);
1707 prb_for_each_record(seq, prb, seq, &r) {
1708 int textlen;
1710 textlen = record_print_text(&r, true, time);
1712 if (len + textlen > size) {
1713 seq--;
1714 break;
1717 if (copy_to_user(buf + len, text, textlen))
1718 len = -EFAULT;
1719 else
1720 len += textlen;
1722 if (len < 0)
1723 break;
1726 if (clear) {
1727 mutex_lock(&syslog_lock);
1728 latched_seq_write(&clear_seq, seq);
1729 mutex_unlock(&syslog_lock);
1732 kfree(text);
1733 return len;
1736 static void syslog_clear(void)
1738 mutex_lock(&syslog_lock);
1739 latched_seq_write(&clear_seq, prb_next_seq(prb));
1740 mutex_unlock(&syslog_lock);
1743 int do_syslog(int type, char __user *buf, int len, int source)
1745 struct printk_info info;
1746 bool clear = false;
1747 static int saved_console_loglevel = LOGLEVEL_DEFAULT;
1748 int error;
1750 error = check_syslog_permissions(type, source);
1751 if (error)
1752 return error;
1754 switch (type) {
1755 case SYSLOG_ACTION_CLOSE: /* Close log */
1756 break;
1757 case SYSLOG_ACTION_OPEN: /* Open log */
1758 break;
1759 case SYSLOG_ACTION_READ: /* Read from log */
1760 if (!buf || len < 0)
1761 return -EINVAL;
1762 if (!len)
1763 return 0;
1764 if (!access_ok(buf, len))
1765 return -EFAULT;
1766 error = syslog_print(buf, len);
1767 break;
1768 /* Read/clear last kernel messages */
1769 case SYSLOG_ACTION_READ_CLEAR:
1770 clear = true;
1771 fallthrough;
1772 /* Read last kernel messages */
1773 case SYSLOG_ACTION_READ_ALL:
1774 if (!buf || len < 0)
1775 return -EINVAL;
1776 if (!len)
1777 return 0;
1778 if (!access_ok(buf, len))
1779 return -EFAULT;
1780 error = syslog_print_all(buf, len, clear);
1781 break;
1782 /* Clear ring buffer */
1783 case SYSLOG_ACTION_CLEAR:
1784 syslog_clear();
1785 break;
1786 /* Disable logging to console */
1787 case SYSLOG_ACTION_CONSOLE_OFF:
1788 if (saved_console_loglevel == LOGLEVEL_DEFAULT)
1789 saved_console_loglevel = console_loglevel;
1790 console_loglevel = minimum_console_loglevel;
1791 break;
1792 /* Enable logging to console */
1793 case SYSLOG_ACTION_CONSOLE_ON:
1794 if (saved_console_loglevel != LOGLEVEL_DEFAULT) {
1795 console_loglevel = saved_console_loglevel;
1796 saved_console_loglevel = LOGLEVEL_DEFAULT;
1798 break;
1799 /* Set level of messages printed to console */
1800 case SYSLOG_ACTION_CONSOLE_LEVEL:
1801 if (len < 1 || len > 8)
1802 return -EINVAL;
1803 if (len < minimum_console_loglevel)
1804 len = minimum_console_loglevel;
1805 console_loglevel = len;
1806 /* Implicitly re-enable logging to console */
1807 saved_console_loglevel = LOGLEVEL_DEFAULT;
1808 break;
1809 /* Number of chars in the log buffer */
1810 case SYSLOG_ACTION_SIZE_UNREAD:
1811 mutex_lock(&syslog_lock);
1812 if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) {
1813 /* No unread messages. */
1814 mutex_unlock(&syslog_lock);
1815 return 0;
1817 if (info.seq != syslog_seq) {
1818 /* messages are gone, move to first one */
1819 syslog_seq = info.seq;
1820 syslog_partial = 0;
1822 if (source == SYSLOG_FROM_PROC) {
1824 * Short-cut for poll(/"proc/kmsg") which simply checks
1825 * for pending data, not the size; return the count of
1826 * records, not the length.
1828 error = prb_next_seq(prb) - syslog_seq;
1829 } else {
1830 bool time = syslog_partial ? syslog_time : printk_time;
1831 unsigned int line_count;
1832 u64 seq;
1834 prb_for_each_info(syslog_seq, prb, seq, &info,
1835 &line_count) {
1836 error += get_record_print_text_size(&info, line_count,
1837 true, time);
1838 time = printk_time;
1840 error -= syslog_partial;
1842 mutex_unlock(&syslog_lock);
1843 break;
1844 /* Size of the log buffer */
1845 case SYSLOG_ACTION_SIZE_BUFFER:
1846 error = log_buf_len;
1847 break;
1848 default:
1849 error = -EINVAL;
1850 break;
1853 return error;
1856 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
1858 return do_syslog(type, buf, len, SYSLOG_FROM_READER);
1862 * Special console_lock variants that help to reduce the risk of soft-lockups.
1863 * They allow to pass console_lock to another printk() call using a busy wait.
1866 #ifdef CONFIG_LOCKDEP
1867 static struct lockdep_map console_owner_dep_map = {
1868 .name = "console_owner"
1870 #endif
1872 static DEFINE_RAW_SPINLOCK(console_owner_lock);
1873 static struct task_struct *console_owner;
1874 static bool console_waiter;
1877 * console_lock_spinning_enable - mark beginning of code where another
1878 * thread might safely busy wait
1880 * This basically converts console_lock into a spinlock. This marks
1881 * the section where the console_lock owner can not sleep, because
1882 * there may be a waiter spinning (like a spinlock). Also it must be
1883 * ready to hand over the lock at the end of the section.
1885 void console_lock_spinning_enable(void)
1888 * Do not use spinning in panic(). The panic CPU wants to keep the lock.
1889 * Non-panic CPUs abandon the flush anyway.
1891 * Just keep the lockdep annotation. The panic-CPU should avoid
1892 * taking console_owner_lock because it might cause a deadlock.
1893 * This looks like the easiest way how to prevent false lockdep
1894 * reports without handling races a lockless way.
1896 if (panic_in_progress())
1897 goto lockdep;
1899 raw_spin_lock(&console_owner_lock);
1900 console_owner = current;
1901 raw_spin_unlock(&console_owner_lock);
1903 lockdep:
1904 /* The waiter may spin on us after setting console_owner */
1905 spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
1909 * console_lock_spinning_disable_and_check - mark end of code where another
1910 * thread was able to busy wait and check if there is a waiter
1911 * @cookie: cookie returned from console_srcu_read_lock()
1913 * This is called at the end of the section where spinning is allowed.
1914 * It has two functions. First, it is a signal that it is no longer
1915 * safe to start busy waiting for the lock. Second, it checks if
1916 * there is a busy waiter and passes the lock rights to her.
1918 * Important: Callers lose both the console_lock and the SRCU read lock if
1919 * there was a busy waiter. They must not touch items synchronized by
1920 * console_lock or SRCU read lock in this case.
1922 * Return: 1 if the lock rights were passed, 0 otherwise.
1924 int console_lock_spinning_disable_and_check(int cookie)
1926 int waiter;
1929 * Ignore spinning waiters during panic() because they might get stopped
1930 * or blocked at any time,
1932 * It is safe because nobody is allowed to start spinning during panic
1933 * in the first place. If there has been a waiter then non panic CPUs
1934 * might stay spinning. They would get stopped anyway. The panic context
1935 * will never start spinning and an interrupted spin on panic CPU will
1936 * never continue.
1938 if (panic_in_progress()) {
1939 /* Keep lockdep happy. */
1940 spin_release(&console_owner_dep_map, _THIS_IP_);
1941 return 0;
1944 raw_spin_lock(&console_owner_lock);
1945 waiter = READ_ONCE(console_waiter);
1946 console_owner = NULL;
1947 raw_spin_unlock(&console_owner_lock);
1949 if (!waiter) {
1950 spin_release(&console_owner_dep_map, _THIS_IP_);
1951 return 0;
1954 /* The waiter is now free to continue */
1955 WRITE_ONCE(console_waiter, false);
1957 spin_release(&console_owner_dep_map, _THIS_IP_);
1960 * Preserve lockdep lock ordering. Release the SRCU read lock before
1961 * releasing the console_lock.
1963 console_srcu_read_unlock(cookie);
1966 * Hand off console_lock to waiter. The waiter will perform
1967 * the up(). After this, the waiter is the console_lock owner.
1969 mutex_release(&console_lock_dep_map, _THIS_IP_);
1970 return 1;
1974 * console_trylock_spinning - try to get console_lock by busy waiting
1976 * This allows to busy wait for the console_lock when the current
1977 * owner is running in specially marked sections. It means that
1978 * the current owner is running and cannot reschedule until it
1979 * is ready to lose the lock.
1981 * Return: 1 if we got the lock, 0 othrewise
1983 static int console_trylock_spinning(void)
1985 struct task_struct *owner = NULL;
1986 bool waiter;
1987 bool spin = false;
1988 unsigned long flags;
1990 if (console_trylock())
1991 return 1;
1994 * It's unsafe to spin once a panic has begun. If we are the
1995 * panic CPU, we may have already halted the owner of the
1996 * console_sem. If we are not the panic CPU, then we should
1997 * avoid taking console_sem, so the panic CPU has a better
1998 * chance of cleanly acquiring it later.
2000 if (panic_in_progress())
2001 return 0;
2003 printk_safe_enter_irqsave(flags);
2005 raw_spin_lock(&console_owner_lock);
2006 owner = READ_ONCE(console_owner);
2007 waiter = READ_ONCE(console_waiter);
2008 if (!waiter && owner && owner != current) {
2009 WRITE_ONCE(console_waiter, true);
2010 spin = true;
2012 raw_spin_unlock(&console_owner_lock);
2015 * If there is an active printk() writing to the
2016 * consoles, instead of having it write our data too,
2017 * see if we can offload that load from the active
2018 * printer, and do some printing ourselves.
2019 * Go into a spin only if there isn't already a waiter
2020 * spinning, and there is an active printer, and
2021 * that active printer isn't us (recursive printk?).
2023 if (!spin) {
2024 printk_safe_exit_irqrestore(flags);
2025 return 0;
2028 /* We spin waiting for the owner to release us */
2029 spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
2030 /* Owner will clear console_waiter on hand off */
2031 while (READ_ONCE(console_waiter))
2032 cpu_relax();
2033 spin_release(&console_owner_dep_map, _THIS_IP_);
2035 printk_safe_exit_irqrestore(flags);
2037 * The owner passed the console lock to us.
2038 * Since we did not spin on console lock, annotate
2039 * this as a trylock. Otherwise lockdep will
2040 * complain.
2042 mutex_acquire(&console_lock_dep_map, 0, 1, _THIS_IP_);
2045 * Update @console_may_schedule for trylock because the previous
2046 * owner may have been schedulable.
2048 console_may_schedule = 0;
2050 return 1;
2054 * Recursion is tracked separately on each CPU. If NMIs are supported, an
2055 * additional NMI context per CPU is also separately tracked. Until per-CPU
2056 * is available, a separate "early tracking" is performed.
2058 static DEFINE_PER_CPU(u8, printk_count);
2059 static u8 printk_count_early;
2060 #ifdef CONFIG_HAVE_NMI
2061 static DEFINE_PER_CPU(u8, printk_count_nmi);
2062 static u8 printk_count_nmi_early;
2063 #endif
2066 * Recursion is limited to keep the output sane. printk() should not require
2067 * more than 1 level of recursion (allowing, for example, printk() to trigger
2068 * a WARN), but a higher value is used in case some printk-internal errors
2069 * exist, such as the ringbuffer validation checks failing.
2071 #define PRINTK_MAX_RECURSION 3
2074 * Return a pointer to the dedicated counter for the CPU+context of the
2075 * caller.
2077 static u8 *__printk_recursion_counter(void)
2079 #ifdef CONFIG_HAVE_NMI
2080 if (in_nmi()) {
2081 if (printk_percpu_data_ready())
2082 return this_cpu_ptr(&printk_count_nmi);
2083 return &printk_count_nmi_early;
2085 #endif
2086 if (printk_percpu_data_ready())
2087 return this_cpu_ptr(&printk_count);
2088 return &printk_count_early;
2092 * Enter recursion tracking. Interrupts are disabled to simplify tracking.
2093 * The caller must check the boolean return value to see if the recursion is
2094 * allowed. On failure, interrupts are not disabled.
2096 * @recursion_ptr must be a variable of type (u8 *) and is the same variable
2097 * that is passed to printk_exit_irqrestore().
2099 #define printk_enter_irqsave(recursion_ptr, flags) \
2100 ({ \
2101 bool success = true; \
2103 typecheck(u8 *, recursion_ptr); \
2104 local_irq_save(flags); \
2105 (recursion_ptr) = __printk_recursion_counter(); \
2106 if (*(recursion_ptr) > PRINTK_MAX_RECURSION) { \
2107 local_irq_restore(flags); \
2108 success = false; \
2109 } else { \
2110 (*(recursion_ptr))++; \
2112 success; \
2115 /* Exit recursion tracking, restoring interrupts. */
2116 #define printk_exit_irqrestore(recursion_ptr, flags) \
2117 do { \
2118 typecheck(u8 *, recursion_ptr); \
2119 (*(recursion_ptr))--; \
2120 local_irq_restore(flags); \
2121 } while (0)
2123 int printk_delay_msec __read_mostly;
2125 static inline void printk_delay(int level)
2127 boot_delay_msec(level);
2129 if (unlikely(printk_delay_msec)) {
2130 int m = printk_delay_msec;
2132 while (m--) {
2133 mdelay(1);
2134 touch_nmi_watchdog();
2139 static inline u32 printk_caller_id(void)
2141 return in_task() ? task_pid_nr(current) :
2142 0x80000000 + smp_processor_id();
2146 * printk_parse_prefix - Parse level and control flags.
2148 * @text: The terminated text message.
2149 * @level: A pointer to the current level value, will be updated.
2150 * @flags: A pointer to the current printk_info flags, will be updated.
2152 * @level may be NULL if the caller is not interested in the parsed value.
2153 * Otherwise the variable pointed to by @level must be set to
2154 * LOGLEVEL_DEFAULT in order to be updated with the parsed value.
2156 * @flags may be NULL if the caller is not interested in the parsed value.
2157 * Otherwise the variable pointed to by @flags will be OR'd with the parsed
2158 * value.
2160 * Return: The length of the parsed level and control flags.
2162 u16 printk_parse_prefix(const char *text, int *level,
2163 enum printk_info_flags *flags)
2165 u16 prefix_len = 0;
2166 int kern_level;
2168 while (*text) {
2169 kern_level = printk_get_level(text);
2170 if (!kern_level)
2171 break;
2173 switch (kern_level) {
2174 case '0' ... '7':
2175 if (level && *level == LOGLEVEL_DEFAULT)
2176 *level = kern_level - '0';
2177 break;
2178 case 'c': /* KERN_CONT */
2179 if (flags)
2180 *flags |= LOG_CONT;
2183 prefix_len += 2;
2184 text += 2;
2187 return prefix_len;
2190 __printf(5, 0)
2191 static u16 printk_sprint(char *text, u16 size, int facility,
2192 enum printk_info_flags *flags, const char *fmt,
2193 va_list args)
2195 u16 text_len;
2197 text_len = vscnprintf(text, size, fmt, args);
2199 /* Mark and strip a trailing newline. */
2200 if (text_len && text[text_len - 1] == '\n') {
2201 text_len--;
2202 *flags |= LOG_NEWLINE;
2205 /* Strip log level and control flags. */
2206 if (facility == 0) {
2207 u16 prefix_len;
2209 prefix_len = printk_parse_prefix(text, NULL, NULL);
2210 if (prefix_len) {
2211 text_len -= prefix_len;
2212 memmove(text, text + prefix_len, text_len);
2216 trace_console(text, text_len);
2218 return text_len;
2221 __printf(4, 0)
2222 int vprintk_store(int facility, int level,
2223 const struct dev_printk_info *dev_info,
2224 const char *fmt, va_list args)
2226 struct prb_reserved_entry e;
2227 enum printk_info_flags flags = 0;
2228 struct printk_record r;
2229 unsigned long irqflags;
2230 u16 trunc_msg_len = 0;
2231 char prefix_buf[8];
2232 u8 *recursion_ptr;
2233 u16 reserve_size;
2234 va_list args2;
2235 u32 caller_id;
2236 u16 text_len;
2237 int ret = 0;
2238 u64 ts_nsec;
2240 if (!printk_enter_irqsave(recursion_ptr, irqflags))
2241 return 0;
2244 * Since the duration of printk() can vary depending on the message
2245 * and state of the ringbuffer, grab the timestamp now so that it is
2246 * close to the call of printk(). This provides a more deterministic
2247 * timestamp with respect to the caller.
2249 ts_nsec = local_clock();
2251 caller_id = printk_caller_id();
2254 * The sprintf needs to come first since the syslog prefix might be
2255 * passed in as a parameter. An extra byte must be reserved so that
2256 * later the vscnprintf() into the reserved buffer has room for the
2257 * terminating '\0', which is not counted by vsnprintf().
2259 va_copy(args2, args);
2260 reserve_size = vsnprintf(&prefix_buf[0], sizeof(prefix_buf), fmt, args2) + 1;
2261 va_end(args2);
2263 if (reserve_size > PRINTKRB_RECORD_MAX)
2264 reserve_size = PRINTKRB_RECORD_MAX;
2266 /* Extract log level or control flags. */
2267 if (facility == 0)
2268 printk_parse_prefix(&prefix_buf[0], &level, &flags);
2270 if (level == LOGLEVEL_DEFAULT)
2271 level = default_message_loglevel;
2273 if (dev_info)
2274 flags |= LOG_NEWLINE;
2276 if (flags & LOG_CONT) {
2277 prb_rec_init_wr(&r, reserve_size);
2278 if (prb_reserve_in_last(&e, prb, &r, caller_id, PRINTKRB_RECORD_MAX)) {
2279 text_len = printk_sprint(&r.text_buf[r.info->text_len], reserve_size,
2280 facility, &flags, fmt, args);
2281 r.info->text_len += text_len;
2283 if (flags & LOG_NEWLINE) {
2284 r.info->flags |= LOG_NEWLINE;
2285 prb_final_commit(&e);
2286 } else {
2287 prb_commit(&e);
2290 ret = text_len;
2291 goto out;
2296 * Explicitly initialize the record before every prb_reserve() call.
2297 * prb_reserve_in_last() and prb_reserve() purposely invalidate the
2298 * structure when they fail.
2300 prb_rec_init_wr(&r, reserve_size);
2301 if (!prb_reserve(&e, prb, &r)) {
2302 /* truncate the message if it is too long for empty buffer */
2303 truncate_msg(&reserve_size, &trunc_msg_len);
2305 prb_rec_init_wr(&r, reserve_size + trunc_msg_len);
2306 if (!prb_reserve(&e, prb, &r))
2307 goto out;
2310 /* fill message */
2311 text_len = printk_sprint(&r.text_buf[0], reserve_size, facility, &flags, fmt, args);
2312 if (trunc_msg_len)
2313 memcpy(&r.text_buf[text_len], trunc_msg, trunc_msg_len);
2314 r.info->text_len = text_len + trunc_msg_len;
2315 r.info->facility = facility;
2316 r.info->level = level & 7;
2317 r.info->flags = flags & 0x1f;
2318 r.info->ts_nsec = ts_nsec;
2319 r.info->caller_id = caller_id;
2320 if (dev_info)
2321 memcpy(&r.info->dev_info, dev_info, sizeof(r.info->dev_info));
2323 /* A message without a trailing newline can be continued. */
2324 if (!(flags & LOG_NEWLINE))
2325 prb_commit(&e);
2326 else
2327 prb_final_commit(&e);
2329 ret = text_len + trunc_msg_len;
2330 out:
2331 printk_exit_irqrestore(recursion_ptr, irqflags);
2332 return ret;
2336 * This acts as a one-way switch to allow legacy consoles to print from
2337 * the printk() caller context on a panic CPU. It also attempts to flush
2338 * the legacy consoles in this context.
2340 void printk_legacy_allow_panic_sync(void)
2342 struct console_flush_type ft;
2344 legacy_allow_panic_sync = true;
2346 printk_get_console_flush_type(&ft);
2347 if (ft.legacy_direct) {
2348 if (console_trylock())
2349 console_unlock();
2353 asmlinkage int vprintk_emit(int facility, int level,
2354 const struct dev_printk_info *dev_info,
2355 const char *fmt, va_list args)
2357 struct console_flush_type ft;
2358 int printed_len;
2360 /* Suppress unimportant messages after panic happens */
2361 if (unlikely(suppress_printk))
2362 return 0;
2365 * The messages on the panic CPU are the most important. If
2366 * non-panic CPUs are generating any messages, they will be
2367 * silently dropped.
2369 if (other_cpu_in_panic() && !panic_triggering_all_cpu_backtrace)
2370 return 0;
2372 printk_get_console_flush_type(&ft);
2374 /* If called from the scheduler, we can not call up(). */
2375 if (level == LOGLEVEL_SCHED) {
2376 level = LOGLEVEL_DEFAULT;
2377 ft.legacy_offload |= ft.legacy_direct;
2378 ft.legacy_direct = false;
2381 printk_delay(level);
2383 printed_len = vprintk_store(facility, level, dev_info, fmt, args);
2385 if (ft.nbcon_atomic)
2386 nbcon_atomic_flush_pending();
2388 if (ft.nbcon_offload)
2389 nbcon_kthreads_wake();
2391 if (ft.legacy_direct) {
2393 * The caller may be holding system-critical or
2394 * timing-sensitive locks. Disable preemption during
2395 * printing of all remaining records to all consoles so that
2396 * this context can return as soon as possible. Hopefully
2397 * another printk() caller will take over the printing.
2399 preempt_disable();
2401 * Try to acquire and then immediately release the console
2402 * semaphore. The release will print out buffers. With the
2403 * spinning variant, this context tries to take over the
2404 * printing from another printing context.
2406 if (console_trylock_spinning())
2407 console_unlock();
2408 preempt_enable();
2411 if (ft.legacy_offload)
2412 defer_console_output();
2413 else
2414 wake_up_klogd();
2416 return printed_len;
2418 EXPORT_SYMBOL(vprintk_emit);
2420 int vprintk_default(const char *fmt, va_list args)
2422 return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, fmt, args);
2424 EXPORT_SYMBOL_GPL(vprintk_default);
2426 asmlinkage __visible int _printk(const char *fmt, ...)
2428 va_list args;
2429 int r;
2431 va_start(args, fmt);
2432 r = vprintk(fmt, args);
2433 va_end(args);
2435 return r;
2437 EXPORT_SYMBOL(_printk);
2439 static bool pr_flush(int timeout_ms, bool reset_on_progress);
2440 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress);
2442 #else /* CONFIG_PRINTK */
2444 #define printk_time false
2446 #define prb_read_valid(rb, seq, r) false
2447 #define prb_first_valid_seq(rb) 0
2448 #define prb_next_seq(rb) 0
2450 static u64 syslog_seq;
2452 static bool pr_flush(int timeout_ms, bool reset_on_progress) { return true; }
2453 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { return true; }
2455 #endif /* CONFIG_PRINTK */
2457 #ifdef CONFIG_EARLY_PRINTK
2458 struct console *early_console;
2460 asmlinkage __visible void early_printk(const char *fmt, ...)
2462 va_list ap;
2463 char buf[512];
2464 int n;
2466 if (!early_console)
2467 return;
2469 va_start(ap, fmt);
2470 n = vscnprintf(buf, sizeof(buf), fmt, ap);
2471 va_end(ap);
2473 early_console->write(early_console, buf, n);
2475 #endif
2477 static void set_user_specified(struct console_cmdline *c, bool user_specified)
2479 if (!user_specified)
2480 return;
2483 * @c console was defined by the user on the command line.
2484 * Do not clear when added twice also by SPCR or the device tree.
2486 c->user_specified = true;
2487 /* At least one console defined by the user on the command line. */
2488 console_set_on_cmdline = 1;
2491 static int __add_preferred_console(const char *name, const short idx,
2492 const char *devname, char *options,
2493 char *brl_options, bool user_specified)
2495 struct console_cmdline *c;
2496 int i;
2498 if (!name && !devname)
2499 return -EINVAL;
2502 * We use a signed short index for struct console for device drivers to
2503 * indicate a not yet assigned index or port. However, a negative index
2504 * value is not valid when the console name and index are defined on
2505 * the command line.
2507 if (name && idx < 0)
2508 return -EINVAL;
2511 * See if this tty is not yet registered, and
2512 * if we have a slot free.
2514 for (i = 0, c = console_cmdline;
2515 i < MAX_CMDLINECONSOLES && (c->name[0] || c->devname[0]);
2516 i++, c++) {
2517 if ((name && strcmp(c->name, name) == 0 && c->index == idx) ||
2518 (devname && strcmp(c->devname, devname) == 0)) {
2519 if (!brl_options)
2520 preferred_console = i;
2521 set_user_specified(c, user_specified);
2522 return 0;
2525 if (i == MAX_CMDLINECONSOLES)
2526 return -E2BIG;
2527 if (!brl_options)
2528 preferred_console = i;
2529 if (name)
2530 strscpy(c->name, name);
2531 if (devname)
2532 strscpy(c->devname, devname);
2533 c->options = options;
2534 set_user_specified(c, user_specified);
2535 braille_set_options(c, brl_options);
2537 c->index = idx;
2538 return 0;
2541 static int __init console_msg_format_setup(char *str)
2543 if (!strcmp(str, "syslog"))
2544 console_msg_format = MSG_FORMAT_SYSLOG;
2545 if (!strcmp(str, "default"))
2546 console_msg_format = MSG_FORMAT_DEFAULT;
2547 return 1;
2549 __setup("console_msg_format=", console_msg_format_setup);
2552 * Set up a console. Called via do_early_param() in init/main.c
2553 * for each "console=" parameter in the boot command line.
2555 static int __init console_setup(char *str)
2557 static_assert(sizeof(console_cmdline[0].devname) >= sizeof(console_cmdline[0].name) + 4);
2558 char buf[sizeof(console_cmdline[0].devname)];
2559 char *brl_options = NULL;
2560 char *ttyname = NULL;
2561 char *devname = NULL;
2562 char *options;
2563 char *s;
2564 int idx;
2567 * console="" or console=null have been suggested as a way to
2568 * disable console output. Use ttynull that has been created
2569 * for exactly this purpose.
2571 if (str[0] == 0 || strcmp(str, "null") == 0) {
2572 __add_preferred_console("ttynull", 0, NULL, NULL, NULL, true);
2573 return 1;
2576 if (_braille_console_setup(&str, &brl_options))
2577 return 1;
2579 /* For a DEVNAME:0.0 style console the character device is unknown early */
2580 if (strchr(str, ':'))
2581 devname = buf;
2582 else
2583 ttyname = buf;
2586 * Decode str into name, index, options.
2588 if (ttyname && isdigit(str[0]))
2589 scnprintf(buf, sizeof(buf), "ttyS%s", str);
2590 else
2591 strscpy(buf, str);
2593 options = strchr(str, ',');
2594 if (options)
2595 *(options++) = 0;
2597 #ifdef __sparc__
2598 if (!strcmp(str, "ttya"))
2599 strscpy(buf, "ttyS0");
2600 if (!strcmp(str, "ttyb"))
2601 strscpy(buf, "ttyS1");
2602 #endif
2604 for (s = buf; *s; s++)
2605 if ((ttyname && isdigit(*s)) || *s == ',')
2606 break;
2608 /* @idx will get defined when devname matches. */
2609 if (devname)
2610 idx = -1;
2611 else
2612 idx = simple_strtoul(s, NULL, 10);
2614 *s = 0;
2616 __add_preferred_console(ttyname, idx, devname, options, brl_options, true);
2617 return 1;
2619 __setup("console=", console_setup);
2622 * add_preferred_console - add a device to the list of preferred consoles.
2623 * @name: device name
2624 * @idx: device index
2625 * @options: options for this console
2627 * The last preferred console added will be used for kernel messages
2628 * and stdin/out/err for init. Normally this is used by console_setup
2629 * above to handle user-supplied console arguments; however it can also
2630 * be used by arch-specific code either to override the user or more
2631 * commonly to provide a default console (ie from PROM variables) when
2632 * the user has not supplied one.
2634 int add_preferred_console(const char *name, const short idx, char *options)
2636 return __add_preferred_console(name, idx, NULL, options, NULL, false);
2640 * match_devname_and_update_preferred_console - Update a preferred console
2641 * when matching devname is found.
2642 * @devname: DEVNAME:0.0 style device name
2643 * @name: Name of the corresponding console driver, e.g. "ttyS"
2644 * @idx: Console index, e.g. port number.
2646 * The function checks whether a device with the given @devname is
2647 * preferred via the console=DEVNAME:0.0 command line option.
2648 * It fills the missing console driver name and console index
2649 * so that a later register_console() call could find (match)
2650 * and enable this device.
2652 * It might be used when a driver subsystem initializes particular
2653 * devices with already known DEVNAME:0.0 style names. And it
2654 * could predict which console driver name and index this device
2655 * would later get associated with.
2657 * Return: 0 on success, negative error code on failure.
2659 int match_devname_and_update_preferred_console(const char *devname,
2660 const char *name,
2661 const short idx)
2663 struct console_cmdline *c = console_cmdline;
2664 int i;
2666 if (!devname || !strlen(devname) || !name || !strlen(name) || idx < 0)
2667 return -EINVAL;
2669 for (i = 0; i < MAX_CMDLINECONSOLES && (c->name[0] || c->devname[0]);
2670 i++, c++) {
2671 if (!strcmp(devname, c->devname)) {
2672 pr_info("associate the preferred console \"%s\" with \"%s%d\"\n",
2673 devname, name, idx);
2674 strscpy(c->name, name);
2675 c->index = idx;
2676 return 0;
2680 return -ENOENT;
2682 EXPORT_SYMBOL_GPL(match_devname_and_update_preferred_console);
2684 bool console_suspend_enabled = true;
2685 EXPORT_SYMBOL(console_suspend_enabled);
2687 static int __init console_suspend_disable(char *str)
2689 console_suspend_enabled = false;
2690 return 1;
2692 __setup("no_console_suspend", console_suspend_disable);
2693 module_param_named(console_suspend, console_suspend_enabled,
2694 bool, S_IRUGO | S_IWUSR);
2695 MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
2696 " and hibernate operations");
2698 static bool printk_console_no_auto_verbose;
2700 void console_verbose(void)
2702 if (console_loglevel && !printk_console_no_auto_verbose)
2703 console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
2705 EXPORT_SYMBOL_GPL(console_verbose);
2707 module_param_named(console_no_auto_verbose, printk_console_no_auto_verbose, bool, 0644);
2708 MODULE_PARM_DESC(console_no_auto_verbose, "Disable console loglevel raise to highest on oops/panic/etc");
2711 * suspend_console - suspend the console subsystem
2713 * This disables printk() while we go into suspend states
2715 void suspend_console(void)
2717 struct console *con;
2719 if (!console_suspend_enabled)
2720 return;
2721 pr_info("Suspending console(s) (use no_console_suspend to debug)\n");
2722 pr_flush(1000, true);
2724 console_list_lock();
2725 for_each_console(con)
2726 console_srcu_write_flags(con, con->flags | CON_SUSPENDED);
2727 console_list_unlock();
2730 * Ensure that all SRCU list walks have completed. All printing
2731 * contexts must be able to see that they are suspended so that it
2732 * is guaranteed that all printing has stopped when this function
2733 * completes.
2735 synchronize_srcu(&console_srcu);
2738 void resume_console(void)
2740 struct console_flush_type ft;
2741 struct console *con;
2743 if (!console_suspend_enabled)
2744 return;
2746 console_list_lock();
2747 for_each_console(con)
2748 console_srcu_write_flags(con, con->flags & ~CON_SUSPENDED);
2749 console_list_unlock();
2752 * Ensure that all SRCU list walks have completed. All printing
2753 * contexts must be able to see they are no longer suspended so
2754 * that they are guaranteed to wake up and resume printing.
2756 synchronize_srcu(&console_srcu);
2758 printk_get_console_flush_type(&ft);
2759 if (ft.nbcon_offload)
2760 nbcon_kthreads_wake();
2761 if (ft.legacy_offload)
2762 defer_console_output();
2764 pr_flush(1000, true);
2768 * console_cpu_notify - print deferred console messages after CPU hotplug
2769 * @cpu: unused
2771 * If printk() is called from a CPU that is not online yet, the messages
2772 * will be printed on the console only if there are CON_ANYTIME consoles.
2773 * This function is called when a new CPU comes online (or fails to come
2774 * up) or goes offline.
2776 static int console_cpu_notify(unsigned int cpu)
2778 struct console_flush_type ft;
2780 if (!cpuhp_tasks_frozen) {
2781 printk_get_console_flush_type(&ft);
2782 if (ft.nbcon_atomic)
2783 nbcon_atomic_flush_pending();
2784 if (ft.legacy_direct) {
2785 if (console_trylock())
2786 console_unlock();
2789 return 0;
2793 * console_lock - block the console subsystem from printing
2795 * Acquires a lock which guarantees that no consoles will
2796 * be in or enter their write() callback.
2798 * Can sleep, returns nothing.
2800 void console_lock(void)
2802 might_sleep();
2804 /* On panic, the console_lock must be left to the panic cpu. */
2805 while (other_cpu_in_panic())
2806 msleep(1000);
2808 down_console_sem();
2809 console_locked = 1;
2810 console_may_schedule = 1;
2812 EXPORT_SYMBOL(console_lock);
2815 * console_trylock - try to block the console subsystem from printing
2817 * Try to acquire a lock which guarantees that no consoles will
2818 * be in or enter their write() callback.
2820 * returns 1 on success, and 0 on failure to acquire the lock.
2822 int console_trylock(void)
2824 /* On panic, the console_lock must be left to the panic cpu. */
2825 if (other_cpu_in_panic())
2826 return 0;
2827 if (down_trylock_console_sem())
2828 return 0;
2829 console_locked = 1;
2830 console_may_schedule = 0;
2831 return 1;
2833 EXPORT_SYMBOL(console_trylock);
2835 int is_console_locked(void)
2837 return console_locked;
2839 EXPORT_SYMBOL(is_console_locked);
2841 static void __console_unlock(void)
2843 console_locked = 0;
2844 up_console_sem();
2847 #ifdef CONFIG_PRINTK
2850 * Prepend the message in @pmsg->pbufs->outbuf. This is achieved by shifting
2851 * the existing message over and inserting the scratchbuf message.
2853 * @pmsg is the original printk message.
2854 * @fmt is the printf format of the message which will prepend the existing one.
2856 * If there is not enough space in @pmsg->pbufs->outbuf, the existing
2857 * message text will be sufficiently truncated.
2859 * If @pmsg->pbufs->outbuf is modified, @pmsg->outbuf_len is updated.
2861 __printf(2, 3)
2862 static void console_prepend_message(struct printk_message *pmsg, const char *fmt, ...)
2864 struct printk_buffers *pbufs = pmsg->pbufs;
2865 const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);
2866 const size_t outbuf_sz = sizeof(pbufs->outbuf);
2867 char *scratchbuf = &pbufs->scratchbuf[0];
2868 char *outbuf = &pbufs->outbuf[0];
2869 va_list args;
2870 size_t len;
2872 va_start(args, fmt);
2873 len = vscnprintf(scratchbuf, scratchbuf_sz, fmt, args);
2874 va_end(args);
2877 * Make sure outbuf is sufficiently large before prepending.
2878 * Keep at least the prefix when the message must be truncated.
2879 * It is a rather theoretical problem when someone tries to
2880 * use a minimalist buffer.
2882 if (WARN_ON_ONCE(len + PRINTK_PREFIX_MAX >= outbuf_sz))
2883 return;
2885 if (pmsg->outbuf_len + len >= outbuf_sz) {
2886 /* Truncate the message, but keep it terminated. */
2887 pmsg->outbuf_len = outbuf_sz - (len + 1);
2888 outbuf[pmsg->outbuf_len] = 0;
2891 memmove(outbuf + len, outbuf, pmsg->outbuf_len + 1);
2892 memcpy(outbuf, scratchbuf, len);
2893 pmsg->outbuf_len += len;
2897 * Prepend the message in @pmsg->pbufs->outbuf with a "dropped message".
2898 * @pmsg->outbuf_len is updated appropriately.
2900 * @pmsg is the printk message to prepend.
2902 * @dropped is the dropped count to report in the dropped message.
2904 void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
2906 console_prepend_message(pmsg, "** %lu printk messages dropped **\n", dropped);
2910 * Prepend the message in @pmsg->pbufs->outbuf with a "replay message".
2911 * @pmsg->outbuf_len is updated appropriately.
2913 * @pmsg is the printk message to prepend.
2915 void console_prepend_replay(struct printk_message *pmsg)
2917 console_prepend_message(pmsg, "** replaying previous printk message **\n");
2921 * Read and format the specified record (or a later record if the specified
2922 * record is not available).
2924 * @pmsg will contain the formatted result. @pmsg->pbufs must point to a
2925 * struct printk_buffers.
2927 * @seq is the record to read and format. If it is not available, the next
2928 * valid record is read.
2930 * @is_extended specifies if the message should be formatted for extended
2931 * console output.
2933 * @may_supress specifies if records may be skipped based on loglevel.
2935 * Returns false if no record is available. Otherwise true and all fields
2936 * of @pmsg are valid. (See the documentation of struct printk_message
2937 * for information about the @pmsg fields.)
2939 bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
2940 bool is_extended, bool may_suppress)
2942 struct printk_buffers *pbufs = pmsg->pbufs;
2943 const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);
2944 const size_t outbuf_sz = sizeof(pbufs->outbuf);
2945 char *scratchbuf = &pbufs->scratchbuf[0];
2946 char *outbuf = &pbufs->outbuf[0];
2947 struct printk_info info;
2948 struct printk_record r;
2949 size_t len = 0;
2952 * Formatting extended messages requires a separate buffer, so use the
2953 * scratch buffer to read in the ringbuffer text.
2955 * Formatting normal messages is done in-place, so read the ringbuffer
2956 * text directly into the output buffer.
2958 if (is_extended)
2959 prb_rec_init_rd(&r, &info, scratchbuf, scratchbuf_sz);
2960 else
2961 prb_rec_init_rd(&r, &info, outbuf, outbuf_sz);
2963 if (!prb_read_valid(prb, seq, &r))
2964 return false;
2966 pmsg->seq = r.info->seq;
2967 pmsg->dropped = r.info->seq - seq;
2969 /* Skip record that has level above the console loglevel. */
2970 if (may_suppress && suppress_message_printing(r.info->level))
2971 goto out;
2973 if (is_extended) {
2974 len = info_print_ext_header(outbuf, outbuf_sz, r.info);
2975 len += msg_print_ext_body(outbuf + len, outbuf_sz - len,
2976 &r.text_buf[0], r.info->text_len, &r.info->dev_info);
2977 } else {
2978 len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time);
2980 out:
2981 pmsg->outbuf_len = len;
2982 return true;
2986 * Legacy console printing from printk() caller context does not respect
2987 * raw_spinlock/spinlock nesting. For !PREEMPT_RT the lockdep warning is a
2988 * false positive. For PREEMPT_RT the false positive condition does not
2989 * occur.
2991 * This map is used to temporarily establish LD_WAIT_SLEEP context for the
2992 * console write() callback when legacy printing to avoid false positive
2993 * lockdep complaints, thus allowing lockdep to continue to function for
2994 * real issues.
2996 #ifdef CONFIG_PREEMPT_RT
2997 static inline void printk_legacy_allow_spinlock_enter(void) { }
2998 static inline void printk_legacy_allow_spinlock_exit(void) { }
2999 #else
3000 static DEFINE_WAIT_OVERRIDE_MAP(printk_legacy_map, LD_WAIT_SLEEP);
3002 static inline void printk_legacy_allow_spinlock_enter(void)
3004 lock_map_acquire_try(&printk_legacy_map);
3007 static inline void printk_legacy_allow_spinlock_exit(void)
3009 lock_map_release(&printk_legacy_map);
3011 #endif /* CONFIG_PREEMPT_RT */
3014 * Used as the printk buffers for non-panic, serialized console printing.
3015 * This is for legacy (!CON_NBCON) as well as all boot (CON_BOOT) consoles.
3016 * Its usage requires the console_lock held.
3018 struct printk_buffers printk_shared_pbufs;
3021 * Print one record for the given console. The record printed is whatever
3022 * record is the next available record for the given console.
3024 * @handover will be set to true if a printk waiter has taken over the
3025 * console_lock, in which case the caller is no longer holding both the
3026 * console_lock and the SRCU read lock. Otherwise it is set to false.
3028 * @cookie is the cookie from the SRCU read lock.
3030 * Returns false if the given console has no next record to print, otherwise
3031 * true.
3033 * Requires the console_lock and the SRCU read lock.
3035 static bool console_emit_next_record(struct console *con, bool *handover, int cookie)
3037 bool is_extended = console_srcu_read_flags(con) & CON_EXTENDED;
3038 char *outbuf = &printk_shared_pbufs.outbuf[0];
3039 struct printk_message pmsg = {
3040 .pbufs = &printk_shared_pbufs,
3042 unsigned long flags;
3044 *handover = false;
3046 if (!printk_get_next_message(&pmsg, con->seq, is_extended, true))
3047 return false;
3049 con->dropped += pmsg.dropped;
3051 /* Skip messages of formatted length 0. */
3052 if (pmsg.outbuf_len == 0) {
3053 con->seq = pmsg.seq + 1;
3054 goto skip;
3057 if (con->dropped && !is_extended) {
3058 console_prepend_dropped(&pmsg, con->dropped);
3059 con->dropped = 0;
3062 /* Write everything out to the hardware. */
3064 if (force_legacy_kthread() && !panic_in_progress()) {
3066 * With forced threading this function is in a task context
3067 * (either legacy kthread or get_init_console_seq()). There
3068 * is no need for concern about printk reentrance, handovers,
3069 * or lockdep complaints.
3072 con->write(con, outbuf, pmsg.outbuf_len);
3073 con->seq = pmsg.seq + 1;
3074 } else {
3076 * While actively printing out messages, if another printk()
3077 * were to occur on another CPU, it may wait for this one to
3078 * finish. This task can not be preempted if there is a
3079 * waiter waiting to take over.
3081 * Interrupts are disabled because the hand over to a waiter
3082 * must not be interrupted until the hand over is completed
3083 * (@console_waiter is cleared).
3085 printk_safe_enter_irqsave(flags);
3086 console_lock_spinning_enable();
3088 /* Do not trace print latency. */
3089 stop_critical_timings();
3091 printk_legacy_allow_spinlock_enter();
3092 con->write(con, outbuf, pmsg.outbuf_len);
3093 printk_legacy_allow_spinlock_exit();
3095 start_critical_timings();
3097 con->seq = pmsg.seq + 1;
3099 *handover = console_lock_spinning_disable_and_check(cookie);
3100 printk_safe_exit_irqrestore(flags);
3102 skip:
3103 return true;
3106 #else
3108 static bool console_emit_next_record(struct console *con, bool *handover, int cookie)
3110 *handover = false;
3111 return false;
3114 static inline void printk_kthreads_check_locked(void) { }
3116 #endif /* CONFIG_PRINTK */
3119 * Print out all remaining records to all consoles.
3121 * @do_cond_resched is set by the caller. It can be true only in schedulable
3122 * context.
3124 * @next_seq is set to the sequence number after the last available record.
3125 * The value is valid only when this function returns true. It means that all
3126 * usable consoles are completely flushed.
3128 * @handover will be set to true if a printk waiter has taken over the
3129 * console_lock, in which case the caller is no longer holding the
3130 * console_lock. Otherwise it is set to false.
3132 * Returns true when there was at least one usable console and all messages
3133 * were flushed to all usable consoles. A returned false informs the caller
3134 * that everything was not flushed (either there were no usable consoles or
3135 * another context has taken over printing or it is a panic situation and this
3136 * is not the panic CPU). Regardless the reason, the caller should assume it
3137 * is not useful to immediately try again.
3139 * Requires the console_lock.
3141 static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handover)
3143 struct console_flush_type ft;
3144 bool any_usable = false;
3145 struct console *con;
3146 bool any_progress;
3147 int cookie;
3149 *next_seq = 0;
3150 *handover = false;
3152 do {
3153 any_progress = false;
3155 printk_get_console_flush_type(&ft);
3157 cookie = console_srcu_read_lock();
3158 for_each_console_srcu(con) {
3159 short flags = console_srcu_read_flags(con);
3160 u64 printk_seq;
3161 bool progress;
3164 * console_flush_all() is only responsible for nbcon
3165 * consoles when the nbcon consoles cannot print via
3166 * their atomic or threaded flushing.
3168 if ((flags & CON_NBCON) && (ft.nbcon_atomic || ft.nbcon_offload))
3169 continue;
3171 if (!console_is_usable(con, flags, !do_cond_resched))
3172 continue;
3173 any_usable = true;
3175 if (flags & CON_NBCON) {
3176 progress = nbcon_legacy_emit_next_record(con, handover, cookie,
3177 !do_cond_resched);
3178 printk_seq = nbcon_seq_read(con);
3179 } else {
3180 progress = console_emit_next_record(con, handover, cookie);
3181 printk_seq = con->seq;
3185 * If a handover has occurred, the SRCU read lock
3186 * is already released.
3188 if (*handover)
3189 return false;
3191 /* Track the next of the highest seq flushed. */
3192 if (printk_seq > *next_seq)
3193 *next_seq = printk_seq;
3195 if (!progress)
3196 continue;
3197 any_progress = true;
3199 /* Allow panic_cpu to take over the consoles safely. */
3200 if (other_cpu_in_panic())
3201 goto abandon;
3203 if (do_cond_resched)
3204 cond_resched();
3206 console_srcu_read_unlock(cookie);
3207 } while (any_progress);
3209 return any_usable;
3211 abandon:
3212 console_srcu_read_unlock(cookie);
3213 return false;
3216 static void __console_flush_and_unlock(void)
3218 bool do_cond_resched;
3219 bool handover;
3220 bool flushed;
3221 u64 next_seq;
3224 * Console drivers are called with interrupts disabled, so
3225 * @console_may_schedule should be cleared before; however, we may
3226 * end up dumping a lot of lines, for example, if called from
3227 * console registration path, and should invoke cond_resched()
3228 * between lines if allowable. Not doing so can cause a very long
3229 * scheduling stall on a slow console leading to RCU stall and
3230 * softlockup warnings which exacerbate the issue with more
3231 * messages practically incapacitating the system. Therefore, create
3232 * a local to use for the printing loop.
3234 do_cond_resched = console_may_schedule;
3236 do {
3237 console_may_schedule = 0;
3239 flushed = console_flush_all(do_cond_resched, &next_seq, &handover);
3240 if (!handover)
3241 __console_unlock();
3244 * Abort if there was a failure to flush all messages to all
3245 * usable consoles. Either it is not possible to flush (in
3246 * which case it would be an infinite loop of retrying) or
3247 * another context has taken over printing.
3249 if (!flushed)
3250 break;
3253 * Some context may have added new records after
3254 * console_flush_all() but before unlocking the console.
3255 * Re-check if there is a new record to flush. If the trylock
3256 * fails, another context is already handling the printing.
3258 } while (prb_read_valid(prb, next_seq, NULL) && console_trylock());
3262 * console_unlock - unblock the legacy console subsystem from printing
3264 * Releases the console_lock which the caller holds to block printing of
3265 * the legacy console subsystem.
3267 * While the console_lock was held, console output may have been buffered
3268 * by printk(). If this is the case, console_unlock() emits the output on
3269 * legacy consoles prior to releasing the lock.
3271 * console_unlock(); may be called from any context.
3273 void console_unlock(void)
3275 struct console_flush_type ft;
3277 printk_get_console_flush_type(&ft);
3278 if (ft.legacy_direct)
3279 __console_flush_and_unlock();
3280 else
3281 __console_unlock();
3283 EXPORT_SYMBOL(console_unlock);
3286 * console_conditional_schedule - yield the CPU if required
3288 * If the console code is currently allowed to sleep, and
3289 * if this CPU should yield the CPU to another task, do
3290 * so here.
3292 * Must be called within console_lock();.
3294 void __sched console_conditional_schedule(void)
3296 if (console_may_schedule)
3297 cond_resched();
3299 EXPORT_SYMBOL(console_conditional_schedule);
3301 void console_unblank(void)
3303 bool found_unblank = false;
3304 struct console *c;
3305 int cookie;
3308 * First check if there are any consoles implementing the unblank()
3309 * callback. If not, there is no reason to continue and take the
3310 * console lock, which in particular can be dangerous if
3311 * @oops_in_progress is set.
3313 cookie = console_srcu_read_lock();
3314 for_each_console_srcu(c) {
3315 if ((console_srcu_read_flags(c) & CON_ENABLED) && c->unblank) {
3316 found_unblank = true;
3317 break;
3320 console_srcu_read_unlock(cookie);
3321 if (!found_unblank)
3322 return;
3325 * Stop console printing because the unblank() callback may
3326 * assume the console is not within its write() callback.
3328 * If @oops_in_progress is set, this may be an atomic context.
3329 * In that case, attempt a trylock as best-effort.
3331 if (oops_in_progress) {
3332 /* Semaphores are not NMI-safe. */
3333 if (in_nmi())
3334 return;
3337 * Attempting to trylock the console lock can deadlock
3338 * if another CPU was stopped while modifying the
3339 * semaphore. "Hope and pray" that this is not the
3340 * current situation.
3342 if (down_trylock_console_sem() != 0)
3343 return;
3344 } else
3345 console_lock();
3347 console_locked = 1;
3348 console_may_schedule = 0;
3350 cookie = console_srcu_read_lock();
3351 for_each_console_srcu(c) {
3352 if ((console_srcu_read_flags(c) & CON_ENABLED) && c->unblank)
3353 c->unblank();
3355 console_srcu_read_unlock(cookie);
3357 console_unlock();
3359 if (!oops_in_progress)
3360 pr_flush(1000, true);
3364 * Rewind all consoles to the oldest available record.
3366 * IMPORTANT: The function is safe only when called under
3367 * console_lock(). It is not enforced because
3368 * it is used as a best effort in panic().
3370 static void __console_rewind_all(void)
3372 struct console *c;
3373 short flags;
3374 int cookie;
3375 u64 seq;
3377 seq = prb_first_valid_seq(prb);
3379 cookie = console_srcu_read_lock();
3380 for_each_console_srcu(c) {
3381 flags = console_srcu_read_flags(c);
3383 if (flags & CON_NBCON) {
3384 nbcon_seq_force(c, seq);
3385 } else {
3387 * This assignment is safe only when called under
3388 * console_lock(). On panic, legacy consoles are
3389 * only best effort.
3391 c->seq = seq;
3394 console_srcu_read_unlock(cookie);
3398 * console_flush_on_panic - flush console content on panic
3399 * @mode: flush all messages in buffer or just the pending ones
3401 * Immediately output all pending messages no matter what.
3403 void console_flush_on_panic(enum con_flush_mode mode)
3405 struct console_flush_type ft;
3406 bool handover;
3407 u64 next_seq;
3410 * Ignore the console lock and flush out the messages. Attempting a
3411 * trylock would not be useful because:
3413 * - if it is contended, it must be ignored anyway
3414 * - console_lock() and console_trylock() block and fail
3415 * respectively in panic for non-panic CPUs
3416 * - semaphores are not NMI-safe
3420 * If another context is holding the console lock,
3421 * @console_may_schedule might be set. Clear it so that
3422 * this context does not call cond_resched() while flushing.
3424 console_may_schedule = 0;
3426 if (mode == CONSOLE_REPLAY_ALL)
3427 __console_rewind_all();
3429 printk_get_console_flush_type(&ft);
3430 if (ft.nbcon_atomic)
3431 nbcon_atomic_flush_pending();
3433 /* Flush legacy consoles once allowed, even when dangerous. */
3434 if (legacy_allow_panic_sync)
3435 console_flush_all(false, &next_seq, &handover);
3439 * Return the console tty driver structure and its associated index
3441 struct tty_driver *console_device(int *index)
3443 struct console *c;
3444 struct tty_driver *driver = NULL;
3445 int cookie;
3448 * Take console_lock to serialize device() callback with
3449 * other console operations. For example, fg_console is
3450 * modified under console_lock when switching vt.
3452 console_lock();
3454 cookie = console_srcu_read_lock();
3455 for_each_console_srcu(c) {
3456 if (!c->device)
3457 continue;
3458 driver = c->device(c, index);
3459 if (driver)
3460 break;
3462 console_srcu_read_unlock(cookie);
3464 console_unlock();
3465 return driver;
3469 * Prevent further output on the passed console device so that (for example)
3470 * serial drivers can disable console output before suspending a port, and can
3471 * re-enable output afterwards.
3473 void console_stop(struct console *console)
3475 __pr_flush(console, 1000, true);
3476 console_list_lock();
3477 console_srcu_write_flags(console, console->flags & ~CON_ENABLED);
3478 console_list_unlock();
3481 * Ensure that all SRCU list walks have completed. All contexts must
3482 * be able to see that this console is disabled so that (for example)
3483 * the caller can suspend the port without risk of another context
3484 * using the port.
3486 synchronize_srcu(&console_srcu);
3488 EXPORT_SYMBOL(console_stop);
3490 void console_start(struct console *console)
3492 struct console_flush_type ft;
3493 bool is_nbcon;
3495 console_list_lock();
3496 console_srcu_write_flags(console, console->flags | CON_ENABLED);
3497 is_nbcon = console->flags & CON_NBCON;
3498 console_list_unlock();
3501 * Ensure that all SRCU list walks have completed. The related
3502 * printing context must be able to see it is enabled so that
3503 * it is guaranteed to wake up and resume printing.
3505 synchronize_srcu(&console_srcu);
3507 printk_get_console_flush_type(&ft);
3508 if (is_nbcon && ft.nbcon_offload)
3509 nbcon_kthread_wake(console);
3510 else if (ft.legacy_offload)
3511 defer_console_output();
3513 __pr_flush(console, 1000, true);
3515 EXPORT_SYMBOL(console_start);
3517 #ifdef CONFIG_PRINTK
3518 static int unregister_console_locked(struct console *console);
3520 /* True when system boot is far enough to create printer threads. */
3521 static bool printk_kthreads_ready __ro_after_init;
3523 static struct task_struct *printk_legacy_kthread;
3525 static bool legacy_kthread_should_wakeup(void)
3527 struct console_flush_type ft;
3528 struct console *con;
3529 bool ret = false;
3530 int cookie;
3532 if (kthread_should_stop())
3533 return true;
3535 printk_get_console_flush_type(&ft);
3537 cookie = console_srcu_read_lock();
3538 for_each_console_srcu(con) {
3539 short flags = console_srcu_read_flags(con);
3540 u64 printk_seq;
3543 * The legacy printer thread is only responsible for nbcon
3544 * consoles when the nbcon consoles cannot print via their
3545 * atomic or threaded flushing.
3547 if ((flags & CON_NBCON) && (ft.nbcon_atomic || ft.nbcon_offload))
3548 continue;
3550 if (!console_is_usable(con, flags, false))
3551 continue;
3553 if (flags & CON_NBCON) {
3554 printk_seq = nbcon_seq_read(con);
3555 } else {
3557 * It is safe to read @seq because only this
3558 * thread context updates @seq.
3560 printk_seq = con->seq;
3563 if (prb_read_valid(prb, printk_seq, NULL)) {
3564 ret = true;
3565 break;
3568 console_srcu_read_unlock(cookie);
3570 return ret;
3573 static int legacy_kthread_func(void *unused)
3575 for (;;) {
3576 wait_event_interruptible(legacy_wait, legacy_kthread_should_wakeup());
3578 if (kthread_should_stop())
3579 break;
3581 console_lock();
3582 __console_flush_and_unlock();
3585 return 0;
3588 static bool legacy_kthread_create(void)
3590 struct task_struct *kt;
3592 lockdep_assert_console_list_lock_held();
3594 kt = kthread_run(legacy_kthread_func, NULL, "pr/legacy");
3595 if (WARN_ON(IS_ERR(kt))) {
3596 pr_err("failed to start legacy printing thread\n");
3597 return false;
3600 printk_legacy_kthread = kt;
3603 * It is important that console printing threads are scheduled
3604 * shortly after a printk call and with generous runtime budgets.
3606 sched_set_normal(printk_legacy_kthread, -20);
3608 return true;
3612 * printk_kthreads_shutdown - shutdown all threaded printers
3614 * On system shutdown all threaded printers are stopped. This allows printk
3615 * to transition back to atomic printing, thus providing a robust mechanism
3616 * for the final shutdown/reboot messages to be output.
3618 static void printk_kthreads_shutdown(void)
3620 struct console *con;
3622 console_list_lock();
3623 if (printk_kthreads_running) {
3624 printk_kthreads_running = false;
3626 for_each_console(con) {
3627 if (con->flags & CON_NBCON)
3628 nbcon_kthread_stop(con);
3632 * The threads may have been stopped while printing a
3633 * backlog. Flush any records left over.
3635 nbcon_atomic_flush_pending();
3637 console_list_unlock();
3640 static struct syscore_ops printk_syscore_ops = {
3641 .shutdown = printk_kthreads_shutdown,
3645 * If appropriate, start nbcon kthreads and set @printk_kthreads_running.
3646 * If any kthreads fail to start, those consoles are unregistered.
3648 * Must be called under console_list_lock().
3650 static void printk_kthreads_check_locked(void)
3652 struct hlist_node *tmp;
3653 struct console *con;
3655 lockdep_assert_console_list_lock_held();
3657 if (!printk_kthreads_ready)
3658 return;
3660 if (have_legacy_console || have_boot_console) {
3661 if (!printk_legacy_kthread &&
3662 force_legacy_kthread() &&
3663 !legacy_kthread_create()) {
3665 * All legacy consoles must be unregistered. If there
3666 * are any nbcon consoles, they will set up their own
3667 * kthread.
3669 hlist_for_each_entry_safe(con, tmp, &console_list, node) {
3670 if (con->flags & CON_NBCON)
3671 continue;
3673 unregister_console_locked(con);
3676 } else if (printk_legacy_kthread) {
3677 kthread_stop(printk_legacy_kthread);
3678 printk_legacy_kthread = NULL;
3682 * Printer threads cannot be started as long as any boot console is
3683 * registered because there is no way to synchronize the hardware
3684 * registers between boot console code and regular console code.
3685 * It can only be known that there will be no new boot consoles when
3686 * an nbcon console is registered.
3688 if (have_boot_console || !have_nbcon_console) {
3689 /* Clear flag in case all nbcon consoles unregistered. */
3690 printk_kthreads_running = false;
3691 return;
3694 if (printk_kthreads_running)
3695 return;
3697 hlist_for_each_entry_safe(con, tmp, &console_list, node) {
3698 if (!(con->flags & CON_NBCON))
3699 continue;
3701 if (!nbcon_kthread_create(con))
3702 unregister_console_locked(con);
3705 printk_kthreads_running = true;
3708 static int __init printk_set_kthreads_ready(void)
3710 register_syscore_ops(&printk_syscore_ops);
3712 console_list_lock();
3713 printk_kthreads_ready = true;
3714 printk_kthreads_check_locked();
3715 console_list_unlock();
3717 return 0;
3719 early_initcall(printk_set_kthreads_ready);
3720 #endif /* CONFIG_PRINTK */
3722 static int __read_mostly keep_bootcon;
3724 static int __init keep_bootcon_setup(char *str)
3726 keep_bootcon = 1;
3727 pr_info("debug: skip boot console de-registration.\n");
3729 return 0;
3732 early_param("keep_bootcon", keep_bootcon_setup);
3734 static int console_call_setup(struct console *newcon, char *options)
3736 int err;
3738 if (!newcon->setup)
3739 return 0;
3741 /* Synchronize with possible boot console. */
3742 console_lock();
3743 err = newcon->setup(newcon, options);
3744 console_unlock();
3746 return err;
3750 * This is called by register_console() to try to match
3751 * the newly registered console with any of the ones selected
3752 * by either the command line or add_preferred_console() and
3753 * setup/enable it.
3755 * Care need to be taken with consoles that are statically
3756 * enabled such as netconsole
3758 static int try_enable_preferred_console(struct console *newcon,
3759 bool user_specified)
3761 struct console_cmdline *c;
3762 int i, err;
3764 for (i = 0, c = console_cmdline;
3765 i < MAX_CMDLINECONSOLES && (c->name[0] || c->devname[0]);
3766 i++, c++) {
3767 /* Console not yet initialized? */
3768 if (!c->name[0])
3769 continue;
3770 if (c->user_specified != user_specified)
3771 continue;
3772 if (!newcon->match ||
3773 newcon->match(newcon, c->name, c->index, c->options) != 0) {
3774 /* default matching */
3775 BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));
3776 if (strcmp(c->name, newcon->name) != 0)
3777 continue;
3778 if (newcon->index >= 0 &&
3779 newcon->index != c->index)
3780 continue;
3781 if (newcon->index < 0)
3782 newcon->index = c->index;
3784 if (_braille_register_console(newcon, c))
3785 return 0;
3787 err = console_call_setup(newcon, c->options);
3788 if (err)
3789 return err;
3791 newcon->flags |= CON_ENABLED;
3792 if (i == preferred_console)
3793 newcon->flags |= CON_CONSDEV;
3794 return 0;
3798 * Some consoles, such as pstore and netconsole, can be enabled even
3799 * without matching. Accept the pre-enabled consoles only when match()
3800 * and setup() had a chance to be called.
3802 if (newcon->flags & CON_ENABLED && c->user_specified == user_specified)
3803 return 0;
3805 return -ENOENT;
3808 /* Try to enable the console unconditionally */
3809 static void try_enable_default_console(struct console *newcon)
3811 if (newcon->index < 0)
3812 newcon->index = 0;
3814 if (console_call_setup(newcon, NULL) != 0)
3815 return;
3817 newcon->flags |= CON_ENABLED;
3819 if (newcon->device)
3820 newcon->flags |= CON_CONSDEV;
3823 /* Return the starting sequence number for a newly registered console. */
3824 static u64 get_init_console_seq(struct console *newcon, bool bootcon_registered)
3826 struct console *con;
3827 bool handover;
3828 u64 init_seq;
3830 if (newcon->flags & (CON_PRINTBUFFER | CON_BOOT)) {
3831 /* Get a consistent copy of @syslog_seq. */
3832 mutex_lock(&syslog_lock);
3833 init_seq = syslog_seq;
3834 mutex_unlock(&syslog_lock);
3835 } else {
3836 /* Begin with next message added to ringbuffer. */
3837 init_seq = prb_next_seq(prb);
3840 * If any enabled boot consoles are due to be unregistered
3841 * shortly, some may not be caught up and may be the same
3842 * device as @newcon. Since it is not known which boot console
3843 * is the same device, flush all consoles and, if necessary,
3844 * start with the message of the enabled boot console that is
3845 * the furthest behind.
3847 if (bootcon_registered && !keep_bootcon) {
3849 * Hold the console_lock to stop console printing and
3850 * guarantee safe access to console->seq.
3852 console_lock();
3855 * Flush all consoles and set the console to start at
3856 * the next unprinted sequence number.
3858 if (!console_flush_all(true, &init_seq, &handover)) {
3860 * Flushing failed. Just choose the lowest
3861 * sequence of the enabled boot consoles.
3865 * If there was a handover, this context no
3866 * longer holds the console_lock.
3868 if (handover)
3869 console_lock();
3871 init_seq = prb_next_seq(prb);
3872 for_each_console(con) {
3873 u64 seq;
3875 if (!(con->flags & CON_BOOT) ||
3876 !(con->flags & CON_ENABLED)) {
3877 continue;
3880 if (con->flags & CON_NBCON)
3881 seq = nbcon_seq_read(con);
3882 else
3883 seq = con->seq;
3885 if (seq < init_seq)
3886 init_seq = seq;
3890 console_unlock();
3894 return init_seq;
3897 #define console_first() \
3898 hlist_entry(console_list.first, struct console, node)
3900 static int unregister_console_locked(struct console *console);
3903 * The console driver calls this routine during kernel initialization
3904 * to register the console printing procedure with printk() and to
3905 * print any messages that were printed by the kernel before the
3906 * console driver was initialized.
3908 * This can happen pretty early during the boot process (because of
3909 * early_printk) - sometimes before setup_arch() completes - be careful
3910 * of what kernel features are used - they may not be initialised yet.
3912 * There are two types of consoles - bootconsoles (early_printk) and
3913 * "real" consoles (everything which is not a bootconsole) which are
3914 * handled differently.
3915 * - Any number of bootconsoles can be registered at any time.
3916 * - As soon as a "real" console is registered, all bootconsoles
3917 * will be unregistered automatically.
3918 * - Once a "real" console is registered, any attempt to register a
3919 * bootconsoles will be rejected
3921 void register_console(struct console *newcon)
3923 bool use_device_lock = (newcon->flags & CON_NBCON) && newcon->write_atomic;
3924 bool bootcon_registered = false;
3925 bool realcon_registered = false;
3926 struct console *con;
3927 unsigned long flags;
3928 u64 init_seq;
3929 int err;
3931 console_list_lock();
3933 for_each_console(con) {
3934 if (WARN(con == newcon, "console '%s%d' already registered\n",
3935 con->name, con->index)) {
3936 goto unlock;
3939 if (con->flags & CON_BOOT)
3940 bootcon_registered = true;
3941 else
3942 realcon_registered = true;
3945 /* Do not register boot consoles when there already is a real one. */
3946 if ((newcon->flags & CON_BOOT) && realcon_registered) {
3947 pr_info("Too late to register bootconsole %s%d\n",
3948 newcon->name, newcon->index);
3949 goto unlock;
3952 if (newcon->flags & CON_NBCON) {
3954 * Ensure the nbcon console buffers can be allocated
3955 * before modifying any global data.
3957 if (!nbcon_alloc(newcon))
3958 goto unlock;
3962 * See if we want to enable this console driver by default.
3964 * Nope when a console is preferred by the command line, device
3965 * tree, or SPCR.
3967 * The first real console with tty binding (driver) wins. More
3968 * consoles might get enabled before the right one is found.
3970 * Note that a console with tty binding will have CON_CONSDEV
3971 * flag set and will be first in the list.
3973 if (preferred_console < 0) {
3974 if (hlist_empty(&console_list) || !console_first()->device ||
3975 console_first()->flags & CON_BOOT) {
3976 try_enable_default_console(newcon);
3980 /* See if this console matches one we selected on the command line */
3981 err = try_enable_preferred_console(newcon, true);
3983 /* If not, try to match against the platform default(s) */
3984 if (err == -ENOENT)
3985 err = try_enable_preferred_console(newcon, false);
3987 /* printk() messages are not printed to the Braille console. */
3988 if (err || newcon->flags & CON_BRL) {
3989 if (newcon->flags & CON_NBCON)
3990 nbcon_free(newcon);
3991 goto unlock;
3995 * If we have a bootconsole, and are switching to a real console,
3996 * don't print everything out again, since when the boot console, and
3997 * the real console are the same physical device, it's annoying to
3998 * see the beginning boot messages twice
4000 if (bootcon_registered &&
4001 ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
4002 newcon->flags &= ~CON_PRINTBUFFER;
4005 newcon->dropped = 0;
4006 init_seq = get_init_console_seq(newcon, bootcon_registered);
4008 if (newcon->flags & CON_NBCON) {
4009 have_nbcon_console = true;
4010 nbcon_seq_force(newcon, init_seq);
4011 } else {
4012 have_legacy_console = true;
4013 newcon->seq = init_seq;
4016 if (newcon->flags & CON_BOOT)
4017 have_boot_console = true;
4020 * If another context is actively using the hardware of this new
4021 * console, it will not be aware of the nbcon synchronization. This
4022 * is a risk that two contexts could access the hardware
4023 * simultaneously if this new console is used for atomic printing
4024 * and the other context is still using the hardware.
4026 * Use the driver synchronization to ensure that the hardware is not
4027 * in use while this new console transitions to being registered.
4029 if (use_device_lock)
4030 newcon->device_lock(newcon, &flags);
4033 * Put this console in the list - keep the
4034 * preferred driver at the head of the list.
4036 if (hlist_empty(&console_list)) {
4037 /* Ensure CON_CONSDEV is always set for the head. */
4038 newcon->flags |= CON_CONSDEV;
4039 hlist_add_head_rcu(&newcon->node, &console_list);
4041 } else if (newcon->flags & CON_CONSDEV) {
4042 /* Only the new head can have CON_CONSDEV set. */
4043 console_srcu_write_flags(console_first(), console_first()->flags & ~CON_CONSDEV);
4044 hlist_add_head_rcu(&newcon->node, &console_list);
4046 } else {
4047 hlist_add_behind_rcu(&newcon->node, console_list.first);
4051 * No need to synchronize SRCU here! The caller does not rely
4052 * on all contexts being able to see the new console before
4053 * register_console() completes.
4056 /* This new console is now registered. */
4057 if (use_device_lock)
4058 newcon->device_unlock(newcon, flags);
4060 console_sysfs_notify();
4063 * By unregistering the bootconsoles after we enable the real console
4064 * we get the "console xxx enabled" message on all the consoles -
4065 * boot consoles, real consoles, etc - this is to ensure that end
4066 * users know there might be something in the kernel's log buffer that
4067 * went to the bootconsole (that they do not see on the real console)
4069 con_printk(KERN_INFO, newcon, "enabled\n");
4070 if (bootcon_registered &&
4071 ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) &&
4072 !keep_bootcon) {
4073 struct hlist_node *tmp;
4075 hlist_for_each_entry_safe(con, tmp, &console_list, node) {
4076 if (con->flags & CON_BOOT)
4077 unregister_console_locked(con);
4081 /* Changed console list, may require printer threads to start/stop. */
4082 printk_kthreads_check_locked();
4083 unlock:
4084 console_list_unlock();
4086 EXPORT_SYMBOL(register_console);
4088 /* Must be called under console_list_lock(). */
4089 static int unregister_console_locked(struct console *console)
4091 bool use_device_lock = (console->flags & CON_NBCON) && console->write_atomic;
4092 bool found_legacy_con = false;
4093 bool found_nbcon_con = false;
4094 bool found_boot_con = false;
4095 unsigned long flags;
4096 struct console *c;
4097 int res;
4099 lockdep_assert_console_list_lock_held();
4101 con_printk(KERN_INFO, console, "disabled\n");
4103 res = _braille_unregister_console(console);
4104 if (res < 0)
4105 return res;
4106 if (res > 0)
4107 return 0;
4109 if (!console_is_registered_locked(console))
4110 res = -ENODEV;
4111 else if (console_is_usable(console, console->flags, true))
4112 __pr_flush(console, 1000, true);
4114 /* Disable it unconditionally */
4115 console_srcu_write_flags(console, console->flags & ~CON_ENABLED);
4117 if (res < 0)
4118 return res;
4121 * Use the driver synchronization to ensure that the hardware is not
4122 * in use while this console transitions to being unregistered.
4124 if (use_device_lock)
4125 console->device_lock(console, &flags);
4127 hlist_del_init_rcu(&console->node);
4129 if (use_device_lock)
4130 console->device_unlock(console, flags);
4133 * <HISTORICAL>
4134 * If this isn't the last console and it has CON_CONSDEV set, we
4135 * need to set it on the next preferred console.
4136 * </HISTORICAL>
4138 * The above makes no sense as there is no guarantee that the next
4139 * console has any device attached. Oh well....
4141 if (!hlist_empty(&console_list) && console->flags & CON_CONSDEV)
4142 console_srcu_write_flags(console_first(), console_first()->flags | CON_CONSDEV);
4145 * Ensure that all SRCU list walks have completed. All contexts
4146 * must not be able to see this console in the list so that any
4147 * exit/cleanup routines can be performed safely.
4149 synchronize_srcu(&console_srcu);
4151 if (console->flags & CON_NBCON)
4152 nbcon_free(console);
4154 console_sysfs_notify();
4156 if (console->exit)
4157 res = console->exit(console);
4160 * With this console gone, the global flags tracking registered
4161 * console types may have changed. Update them.
4163 for_each_console(c) {
4164 if (c->flags & CON_BOOT)
4165 found_boot_con = true;
4167 if (c->flags & CON_NBCON)
4168 found_nbcon_con = true;
4169 else
4170 found_legacy_con = true;
4172 if (!found_boot_con)
4173 have_boot_console = found_boot_con;
4174 if (!found_legacy_con)
4175 have_legacy_console = found_legacy_con;
4176 if (!found_nbcon_con)
4177 have_nbcon_console = found_nbcon_con;
4179 /* Changed console list, may require printer threads to start/stop. */
4180 printk_kthreads_check_locked();
4182 return res;
4185 int unregister_console(struct console *console)
4187 int res;
4189 console_list_lock();
4190 res = unregister_console_locked(console);
4191 console_list_unlock();
4192 return res;
4194 EXPORT_SYMBOL(unregister_console);
4197 * console_force_preferred_locked - force a registered console preferred
4198 * @con: The registered console to force preferred.
4200 * Must be called under console_list_lock().
4202 void console_force_preferred_locked(struct console *con)
4204 struct console *cur_pref_con;
4206 if (!console_is_registered_locked(con))
4207 return;
4209 cur_pref_con = console_first();
4211 /* Already preferred? */
4212 if (cur_pref_con == con)
4213 return;
4216 * Delete, but do not re-initialize the entry. This allows the console
4217 * to continue to appear registered (via any hlist_unhashed_lockless()
4218 * checks), even though it was briefly removed from the console list.
4220 hlist_del_rcu(&con->node);
4223 * Ensure that all SRCU list walks have completed so that the console
4224 * can be added to the beginning of the console list and its forward
4225 * list pointer can be re-initialized.
4227 synchronize_srcu(&console_srcu);
4229 con->flags |= CON_CONSDEV;
4230 WARN_ON(!con->device);
4232 /* Only the new head can have CON_CONSDEV set. */
4233 console_srcu_write_flags(cur_pref_con, cur_pref_con->flags & ~CON_CONSDEV);
4234 hlist_add_head_rcu(&con->node, &console_list);
4236 EXPORT_SYMBOL(console_force_preferred_locked);
4239 * Initialize the console device. This is called *early*, so
4240 * we can't necessarily depend on lots of kernel help here.
4241 * Just do some early initializations, and do the complex setup
4242 * later.
4244 void __init console_init(void)
4246 int ret;
4247 initcall_t call;
4248 initcall_entry_t *ce;
4250 /* Setup the default TTY line discipline. */
4251 n_tty_init();
4254 * set up the console device so that later boot sequences can
4255 * inform about problems etc..
4257 ce = __con_initcall_start;
4258 trace_initcall_level("console");
4259 while (ce < __con_initcall_end) {
4260 call = initcall_from_entry(ce);
4261 trace_initcall_start(call);
4262 ret = call();
4263 trace_initcall_finish(call, ret);
4264 ce++;
4269 * Some boot consoles access data that is in the init section and which will
4270 * be discarded after the initcalls have been run. To make sure that no code
4271 * will access this data, unregister the boot consoles in a late initcall.
4273 * If for some reason, such as deferred probe or the driver being a loadable
4274 * module, the real console hasn't registered yet at this point, there will
4275 * be a brief interval in which no messages are logged to the console, which
4276 * makes it difficult to diagnose problems that occur during this time.
4278 * To mitigate this problem somewhat, only unregister consoles whose memory
4279 * intersects with the init section. Note that all other boot consoles will
4280 * get unregistered when the real preferred console is registered.
4282 static int __init printk_late_init(void)
4284 struct hlist_node *tmp;
4285 struct console *con;
4286 int ret;
4288 console_list_lock();
4289 hlist_for_each_entry_safe(con, tmp, &console_list, node) {
4290 if (!(con->flags & CON_BOOT))
4291 continue;
4293 /* Check addresses that might be used for enabled consoles. */
4294 if (init_section_intersects(con, sizeof(*con)) ||
4295 init_section_contains(con->write, 0) ||
4296 init_section_contains(con->read, 0) ||
4297 init_section_contains(con->device, 0) ||
4298 init_section_contains(con->unblank, 0) ||
4299 init_section_contains(con->data, 0)) {
4301 * Please, consider moving the reported consoles out
4302 * of the init section.
4304 pr_warn("bootconsole [%s%d] uses init memory and must be disabled even before the real one is ready\n",
4305 con->name, con->index);
4306 unregister_console_locked(con);
4309 console_list_unlock();
4311 ret = cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD, "printk:dead", NULL,
4312 console_cpu_notify);
4313 WARN_ON(ret < 0);
4314 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "printk:online",
4315 console_cpu_notify, NULL);
4316 WARN_ON(ret < 0);
4317 printk_sysctl_init();
4318 return 0;
4320 late_initcall(printk_late_init);
4322 #if defined CONFIG_PRINTK
4323 /* If @con is specified, only wait for that console. Otherwise wait for all. */
4324 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress)
4326 unsigned long timeout_jiffies = msecs_to_jiffies(timeout_ms);
4327 unsigned long remaining_jiffies = timeout_jiffies;
4328 struct console_flush_type ft;
4329 struct console *c;
4330 u64 last_diff = 0;
4331 u64 printk_seq;
4332 short flags;
4333 int cookie;
4334 u64 diff;
4335 u64 seq;
4337 /* Sorry, pr_flush() will not work this early. */
4338 if (system_state < SYSTEM_SCHEDULING)
4339 return false;
4341 might_sleep();
4343 seq = prb_next_reserve_seq(prb);
4345 /* Flush the consoles so that records up to @seq are printed. */
4346 printk_get_console_flush_type(&ft);
4347 if (ft.nbcon_atomic)
4348 nbcon_atomic_flush_pending();
4349 if (ft.legacy_direct) {
4350 console_lock();
4351 console_unlock();
4354 for (;;) {
4355 unsigned long begin_jiffies;
4356 unsigned long slept_jiffies;
4358 diff = 0;
4361 * Hold the console_lock to guarantee safe access to
4362 * console->seq. Releasing console_lock flushes more
4363 * records in case @seq is still not printed on all
4364 * usable consoles.
4366 * Holding the console_lock is not necessary if there
4367 * are no legacy or boot consoles. However, such a
4368 * console could register at any time. Always hold the
4369 * console_lock as a precaution rather than
4370 * synchronizing against register_console().
4372 console_lock();
4374 cookie = console_srcu_read_lock();
4375 for_each_console_srcu(c) {
4376 if (con && con != c)
4377 continue;
4379 flags = console_srcu_read_flags(c);
4382 * If consoles are not usable, it cannot be expected
4383 * that they make forward progress, so only increment
4384 * @diff for usable consoles.
4386 if (!console_is_usable(c, flags, true) &&
4387 !console_is_usable(c, flags, false)) {
4388 continue;
4391 if (flags & CON_NBCON) {
4392 printk_seq = nbcon_seq_read(c);
4393 } else {
4394 printk_seq = c->seq;
4397 if (printk_seq < seq)
4398 diff += seq - printk_seq;
4400 console_srcu_read_unlock(cookie);
4402 if (diff != last_diff && reset_on_progress)
4403 remaining_jiffies = timeout_jiffies;
4405 console_unlock();
4407 /* Note: @diff is 0 if there are no usable consoles. */
4408 if (diff == 0 || remaining_jiffies == 0)
4409 break;
4411 /* msleep(1) might sleep much longer. Check time by jiffies. */
4412 begin_jiffies = jiffies;
4413 msleep(1);
4414 slept_jiffies = jiffies - begin_jiffies;
4416 remaining_jiffies -= min(slept_jiffies, remaining_jiffies);
4418 last_diff = diff;
4421 return (diff == 0);
4425 * pr_flush() - Wait for printing threads to catch up.
4427 * @timeout_ms: The maximum time (in ms) to wait.
4428 * @reset_on_progress: Reset the timeout if forward progress is seen.
4430 * A value of 0 for @timeout_ms means no waiting will occur. A value of -1
4431 * represents infinite waiting.
4433 * If @reset_on_progress is true, the timeout will be reset whenever any
4434 * printer has been seen to make some forward progress.
4436 * Context: Process context. May sleep while acquiring console lock.
4437 * Return: true if all usable printers are caught up.
4439 static bool pr_flush(int timeout_ms, bool reset_on_progress)
4441 return __pr_flush(NULL, timeout_ms, reset_on_progress);
4445 * Delayed printk version, for scheduler-internal messages:
4447 #define PRINTK_PENDING_WAKEUP 0x01
4448 #define PRINTK_PENDING_OUTPUT 0x02
4450 static DEFINE_PER_CPU(int, printk_pending);
4452 static void wake_up_klogd_work_func(struct irq_work *irq_work)
4454 int pending = this_cpu_xchg(printk_pending, 0);
4456 if (pending & PRINTK_PENDING_OUTPUT) {
4457 if (force_legacy_kthread()) {
4458 if (printk_legacy_kthread)
4459 wake_up_interruptible(&legacy_wait);
4460 } else {
4461 if (console_trylock())
4462 console_unlock();
4466 if (pending & PRINTK_PENDING_WAKEUP)
4467 wake_up_interruptible(&log_wait);
4470 static DEFINE_PER_CPU(struct irq_work, wake_up_klogd_work) =
4471 IRQ_WORK_INIT_LAZY(wake_up_klogd_work_func);
4473 static void __wake_up_klogd(int val)
4475 if (!printk_percpu_data_ready())
4476 return;
4478 preempt_disable();
4480 * Guarantee any new records can be seen by tasks preparing to wait
4481 * before this context checks if the wait queue is empty.
4483 * The full memory barrier within wq_has_sleeper() pairs with the full
4484 * memory barrier within set_current_state() of
4485 * prepare_to_wait_event(), which is called after ___wait_event() adds
4486 * the waiter but before it has checked the wait condition.
4488 * This pairs with devkmsg_read:A and syslog_print:A.
4490 if (wq_has_sleeper(&log_wait) || /* LMM(__wake_up_klogd:A) */
4491 (val & PRINTK_PENDING_OUTPUT)) {
4492 this_cpu_or(printk_pending, val);
4493 irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
4495 preempt_enable();
4499 * wake_up_klogd - Wake kernel logging daemon
4501 * Use this function when new records have been added to the ringbuffer
4502 * and the console printing of those records has already occurred or is
4503 * known to be handled by some other context. This function will only
4504 * wake the logging daemon.
4506 * Context: Any context.
4508 void wake_up_klogd(void)
4510 __wake_up_klogd(PRINTK_PENDING_WAKEUP);
4514 * defer_console_output - Wake kernel logging daemon and trigger
4515 * console printing in a deferred context
4517 * Use this function when new records have been added to the ringbuffer,
4518 * this context is responsible for console printing those records, but
4519 * the current context is not allowed to perform the console printing.
4520 * Trigger an irq_work context to perform the console printing. This
4521 * function also wakes the logging daemon.
4523 * Context: Any context.
4525 void defer_console_output(void)
4528 * New messages may have been added directly to the ringbuffer
4529 * using vprintk_store(), so wake any waiters as well.
4531 __wake_up_klogd(PRINTK_PENDING_WAKEUP | PRINTK_PENDING_OUTPUT);
4534 void printk_trigger_flush(void)
4536 defer_console_output();
4539 int vprintk_deferred(const char *fmt, va_list args)
4541 return vprintk_emit(0, LOGLEVEL_SCHED, NULL, fmt, args);
4544 int _printk_deferred(const char *fmt, ...)
4546 va_list args;
4547 int r;
4549 va_start(args, fmt);
4550 r = vprintk_deferred(fmt, args);
4551 va_end(args);
4553 return r;
4557 * printk rate limiting, lifted from the networking subsystem.
4559 * This enforces a rate limit: not more than 10 kernel messages
4560 * every 5s to make a denial-of-service attack impossible.
4562 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
4564 int __printk_ratelimit(const char *func)
4566 return ___ratelimit(&printk_ratelimit_state, func);
4568 EXPORT_SYMBOL(__printk_ratelimit);
4571 * printk_timed_ratelimit - caller-controlled printk ratelimiting
4572 * @caller_jiffies: pointer to caller's state
4573 * @interval_msecs: minimum interval between prints
4575 * printk_timed_ratelimit() returns true if more than @interval_msecs
4576 * milliseconds have elapsed since the last time printk_timed_ratelimit()
4577 * returned true.
4579 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
4580 unsigned int interval_msecs)
4582 unsigned long elapsed = jiffies - *caller_jiffies;
4584 if (*caller_jiffies && elapsed <= msecs_to_jiffies(interval_msecs))
4585 return false;
4587 *caller_jiffies = jiffies;
4588 return true;
4590 EXPORT_SYMBOL(printk_timed_ratelimit);
4592 static DEFINE_SPINLOCK(dump_list_lock);
4593 static LIST_HEAD(dump_list);
4596 * kmsg_dump_register - register a kernel log dumper.
4597 * @dumper: pointer to the kmsg_dumper structure
4599 * Adds a kernel log dumper to the system. The dump callback in the
4600 * structure will be called when the kernel oopses or panics and must be
4601 * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
4603 int kmsg_dump_register(struct kmsg_dumper *dumper)
4605 unsigned long flags;
4606 int err = -EBUSY;
4608 /* The dump callback needs to be set */
4609 if (!dumper->dump)
4610 return -EINVAL;
4612 spin_lock_irqsave(&dump_list_lock, flags);
4613 /* Don't allow registering multiple times */
4614 if (!dumper->registered) {
4615 dumper->registered = 1;
4616 list_add_tail_rcu(&dumper->list, &dump_list);
4617 err = 0;
4619 spin_unlock_irqrestore(&dump_list_lock, flags);
4621 return err;
4623 EXPORT_SYMBOL_GPL(kmsg_dump_register);
4626 * kmsg_dump_unregister - unregister a kmsg dumper.
4627 * @dumper: pointer to the kmsg_dumper structure
4629 * Removes a dump device from the system. Returns zero on success and
4630 * %-EINVAL otherwise.
4632 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
4634 unsigned long flags;
4635 int err = -EINVAL;
4637 spin_lock_irqsave(&dump_list_lock, flags);
4638 if (dumper->registered) {
4639 dumper->registered = 0;
4640 list_del_rcu(&dumper->list);
4641 err = 0;
4643 spin_unlock_irqrestore(&dump_list_lock, flags);
4644 synchronize_rcu();
4646 return err;
4648 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
4650 static bool always_kmsg_dump;
4651 module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);
4653 const char *kmsg_dump_reason_str(enum kmsg_dump_reason reason)
4655 switch (reason) {
4656 case KMSG_DUMP_PANIC:
4657 return "Panic";
4658 case KMSG_DUMP_OOPS:
4659 return "Oops";
4660 case KMSG_DUMP_EMERG:
4661 return "Emergency";
4662 case KMSG_DUMP_SHUTDOWN:
4663 return "Shutdown";
4664 default:
4665 return "Unknown";
4668 EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
4671 * kmsg_dump_desc - dump kernel log to kernel message dumpers.
4672 * @reason: the reason (oops, panic etc) for dumping
4673 * @desc: a short string to describe what caused the panic or oops. Can be NULL
4674 * if no additional description is available.
4676 * Call each of the registered dumper's dump() callback, which can
4677 * retrieve the kmsg records with kmsg_dump_get_line() or
4678 * kmsg_dump_get_buffer().
4680 void kmsg_dump_desc(enum kmsg_dump_reason reason, const char *desc)
4682 struct kmsg_dumper *dumper;
4683 struct kmsg_dump_detail detail = {
4684 .reason = reason,
4685 .description = desc};
4687 rcu_read_lock();
4688 list_for_each_entry_rcu(dumper, &dump_list, list) {
4689 enum kmsg_dump_reason max_reason = dumper->max_reason;
4692 * If client has not provided a specific max_reason, default
4693 * to KMSG_DUMP_OOPS, unless always_kmsg_dump was set.
4695 if (max_reason == KMSG_DUMP_UNDEF) {
4696 max_reason = always_kmsg_dump ? KMSG_DUMP_MAX :
4697 KMSG_DUMP_OOPS;
4699 if (reason > max_reason)
4700 continue;
4702 /* invoke dumper which will iterate over records */
4703 dumper->dump(dumper, &detail);
4705 rcu_read_unlock();
4709 * kmsg_dump_get_line - retrieve one kmsg log line
4710 * @iter: kmsg dump iterator
4711 * @syslog: include the "<4>" prefixes
4712 * @line: buffer to copy the line to
4713 * @size: maximum size of the buffer
4714 * @len: length of line placed into buffer
4716 * Start at the beginning of the kmsg buffer, with the oldest kmsg
4717 * record, and copy one record into the provided buffer.
4719 * Consecutive calls will return the next available record moving
4720 * towards the end of the buffer with the youngest messages.
4722 * A return value of FALSE indicates that there are no more records to
4723 * read.
4725 bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
4726 char *line, size_t size, size_t *len)
4728 u64 min_seq = latched_seq_read_nolock(&clear_seq);
4729 struct printk_info info;
4730 unsigned int line_count;
4731 struct printk_record r;
4732 size_t l = 0;
4733 bool ret = false;
4735 if (iter->cur_seq < min_seq)
4736 iter->cur_seq = min_seq;
4738 prb_rec_init_rd(&r, &info, line, size);
4740 /* Read text or count text lines? */
4741 if (line) {
4742 if (!prb_read_valid(prb, iter->cur_seq, &r))
4743 goto out;
4744 l = record_print_text(&r, syslog, printk_time);
4745 } else {
4746 if (!prb_read_valid_info(prb, iter->cur_seq,
4747 &info, &line_count)) {
4748 goto out;
4750 l = get_record_print_text_size(&info, line_count, syslog,
4751 printk_time);
4755 iter->cur_seq = r.info->seq + 1;
4756 ret = true;
4757 out:
4758 if (len)
4759 *len = l;
4760 return ret;
4762 EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
4765 * kmsg_dump_get_buffer - copy kmsg log lines
4766 * @iter: kmsg dump iterator
4767 * @syslog: include the "<4>" prefixes
4768 * @buf: buffer to copy the line to
4769 * @size: maximum size of the buffer
4770 * @len_out: length of line placed into buffer
4772 * Start at the end of the kmsg buffer and fill the provided buffer
4773 * with as many of the *youngest* kmsg records that fit into it.
4774 * If the buffer is large enough, all available kmsg records will be
4775 * copied with a single call.
4777 * Consecutive calls will fill the buffer with the next block of
4778 * available older records, not including the earlier retrieved ones.
4780 * A return value of FALSE indicates that there are no more records to
4781 * read.
4783 bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
4784 char *buf, size_t size, size_t *len_out)
4786 u64 min_seq = latched_seq_read_nolock(&clear_seq);
4787 struct printk_info info;
4788 struct printk_record r;
4789 u64 seq;
4790 u64 next_seq;
4791 size_t len = 0;
4792 bool ret = false;
4793 bool time = printk_time;
4795 if (!buf || !size)
4796 goto out;
4798 if (iter->cur_seq < min_seq)
4799 iter->cur_seq = min_seq;
4801 if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
4802 if (info.seq != iter->cur_seq) {
4803 /* messages are gone, move to first available one */
4804 iter->cur_seq = info.seq;
4808 /* last entry */
4809 if (iter->cur_seq >= iter->next_seq)
4810 goto out;
4813 * Find first record that fits, including all following records,
4814 * into the user-provided buffer for this dump. Pass in size-1
4815 * because this function (by way of record_print_text()) will
4816 * not write more than size-1 bytes of text into @buf.
4818 seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,
4819 size - 1, syslog, time);
4822 * Next kmsg_dump_get_buffer() invocation will dump block of
4823 * older records stored right before this one.
4825 next_seq = seq;
4827 prb_rec_init_rd(&r, &info, buf, size);
4829 prb_for_each_record(seq, prb, seq, &r) {
4830 if (r.info->seq >= iter->next_seq)
4831 break;
4833 len += record_print_text(&r, syslog, time);
4835 /* Adjust record to store to remaining buffer space. */
4836 prb_rec_init_rd(&r, &info, buf + len, size - len);
4839 iter->next_seq = next_seq;
4840 ret = true;
4841 out:
4842 if (len_out)
4843 *len_out = len;
4844 return ret;
4846 EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
4849 * kmsg_dump_rewind - reset the iterator
4850 * @iter: kmsg dump iterator
4852 * Reset the dumper's iterator so that kmsg_dump_get_line() and
4853 * kmsg_dump_get_buffer() can be called again and used multiple
4854 * times within the same dumper.dump() callback.
4856 void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
4858 iter->cur_seq = latched_seq_read_nolock(&clear_seq);
4859 iter->next_seq = prb_next_seq(prb);
4861 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
4864 * console_try_replay_all - try to replay kernel log on consoles
4866 * Try to obtain lock on console subsystem and replay all
4867 * available records in printk buffer on the consoles.
4868 * Does nothing if lock is not obtained.
4870 * Context: Any, except for NMI.
4872 void console_try_replay_all(void)
4874 struct console_flush_type ft;
4876 printk_get_console_flush_type(&ft);
4877 if (console_trylock()) {
4878 __console_rewind_all();
4879 if (ft.nbcon_atomic)
4880 nbcon_atomic_flush_pending();
4881 if (ft.nbcon_offload)
4882 nbcon_kthreads_wake();
4883 if (ft.legacy_offload)
4884 defer_console_output();
4885 /* Consoles are flushed as part of console_unlock(). */
4886 console_unlock();
4889 #endif
4891 #ifdef CONFIG_SMP
4892 static atomic_t printk_cpu_sync_owner = ATOMIC_INIT(-1);
4893 static atomic_t printk_cpu_sync_nested = ATOMIC_INIT(0);
4896 * __printk_cpu_sync_wait() - Busy wait until the printk cpu-reentrant
4897 * spinning lock is not owned by any CPU.
4899 * Context: Any context.
4901 void __printk_cpu_sync_wait(void)
4903 do {
4904 cpu_relax();
4905 } while (atomic_read(&printk_cpu_sync_owner) != -1);
4907 EXPORT_SYMBOL(__printk_cpu_sync_wait);
4910 * __printk_cpu_sync_try_get() - Try to acquire the printk cpu-reentrant
4911 * spinning lock.
4913 * If no processor has the lock, the calling processor takes the lock and
4914 * becomes the owner. If the calling processor is already the owner of the
4915 * lock, this function succeeds immediately.
4917 * Context: Any context. Expects interrupts to be disabled.
4918 * Return: 1 on success, otherwise 0.
4920 int __printk_cpu_sync_try_get(void)
4922 int cpu;
4923 int old;
4925 cpu = smp_processor_id();
4928 * Guarantee loads and stores from this CPU when it is the lock owner
4929 * are _not_ visible to the previous lock owner. This pairs with
4930 * __printk_cpu_sync_put:B.
4932 * Memory barrier involvement:
4934 * If __printk_cpu_sync_try_get:A reads from __printk_cpu_sync_put:B,
4935 * then __printk_cpu_sync_put:A can never read from
4936 * __printk_cpu_sync_try_get:B.
4938 * Relies on:
4940 * RELEASE from __printk_cpu_sync_put:A to __printk_cpu_sync_put:B
4941 * of the previous CPU
4942 * matching
4943 * ACQUIRE from __printk_cpu_sync_try_get:A to
4944 * __printk_cpu_sync_try_get:B of this CPU
4946 old = atomic_cmpxchg_acquire(&printk_cpu_sync_owner, -1,
4947 cpu); /* LMM(__printk_cpu_sync_try_get:A) */
4948 if (old == -1) {
4950 * This CPU is now the owner and begins loading/storing
4951 * data: LMM(__printk_cpu_sync_try_get:B)
4953 return 1;
4955 } else if (old == cpu) {
4956 /* This CPU is already the owner. */
4957 atomic_inc(&printk_cpu_sync_nested);
4958 return 1;
4961 return 0;
4963 EXPORT_SYMBOL(__printk_cpu_sync_try_get);
4966 * __printk_cpu_sync_put() - Release the printk cpu-reentrant spinning lock.
4968 * The calling processor must be the owner of the lock.
4970 * Context: Any context. Expects interrupts to be disabled.
4972 void __printk_cpu_sync_put(void)
4974 if (atomic_read(&printk_cpu_sync_nested)) {
4975 atomic_dec(&printk_cpu_sync_nested);
4976 return;
4980 * This CPU is finished loading/storing data:
4981 * LMM(__printk_cpu_sync_put:A)
4985 * Guarantee loads and stores from this CPU when it was the
4986 * lock owner are visible to the next lock owner. This pairs
4987 * with __printk_cpu_sync_try_get:A.
4989 * Memory barrier involvement:
4991 * If __printk_cpu_sync_try_get:A reads from __printk_cpu_sync_put:B,
4992 * then __printk_cpu_sync_try_get:B reads from __printk_cpu_sync_put:A.
4994 * Relies on:
4996 * RELEASE from __printk_cpu_sync_put:A to __printk_cpu_sync_put:B
4997 * of this CPU
4998 * matching
4999 * ACQUIRE from __printk_cpu_sync_try_get:A to
5000 * __printk_cpu_sync_try_get:B of the next CPU
5002 atomic_set_release(&printk_cpu_sync_owner,
5003 -1); /* LMM(__printk_cpu_sync_put:B) */
5005 EXPORT_SYMBOL(__printk_cpu_sync_put);
5006 #endif /* CONFIG_SMP */