1 // SPDX-License-Identifier: GPL-2.0-only
3 * linux/kernel/printk.c
5 * Copyright (C) 1991, 1992 Linus Torvalds
7 * Modified to make sys_syslog() more flexible: added commands to
8 * return the last 4k of kernel messages, regardless of whether
9 * they've been read or not. Added option to suppress kernel printk's
10 * to the console. Added hook for sending the console messages
11 * elsewhere, in preparation for a serial line console (someday).
13 * Modified for sysctl support, 1/8/97, Chris Horn.
14 * Fixed SMP synchronization, 08/08/99, Manfred Spraul
15 * manfred@colorfullife.com
16 * Rewrote bits to get rid of console_lock
17 * 01Mar01 Andrew Morton
20 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
22 #include <linux/kernel.h>
24 #include <linux/tty.h>
25 #include <linux/tty_driver.h>
26 #include <linux/console.h>
27 #include <linux/init.h>
28 #include <linux/jiffies.h>
29 #include <linux/nmi.h>
30 #include <linux/module.h>
31 #include <linux/moduleparam.h>
32 #include <linux/delay.h>
33 #include <linux/smp.h>
34 #include <linux/security.h>
35 #include <linux/memblock.h>
36 #include <linux/syscalls.h>
37 #include <linux/crash_core.h>
38 #include <linux/ratelimit.h>
39 #include <linux/kmsg_dump.h>
40 #include <linux/syslog.h>
41 #include <linux/cpu.h>
42 #include <linux/rculist.h>
43 #include <linux/poll.h>
44 #include <linux/irq_work.h>
45 #include <linux/ctype.h>
46 #include <linux/uio.h>
47 #include <linux/sched/clock.h>
48 #include <linux/sched/debug.h>
49 #include <linux/sched/task_stack.h>
51 #include <linux/uaccess.h>
52 #include <asm/sections.h>
54 #include <trace/events/initcall.h>
55 #define CREATE_TRACE_POINTS
56 #include <trace/events/printk.h>
58 #include "printk_ringbuffer.h"
59 #include "console_cmdline.h"
63 int console_printk[4] = {
64 CONSOLE_LOGLEVEL_DEFAULT, /* console_loglevel */
65 MESSAGE_LOGLEVEL_DEFAULT, /* default_message_loglevel */
66 CONSOLE_LOGLEVEL_MIN, /* minimum_console_loglevel */
67 CONSOLE_LOGLEVEL_DEFAULT, /* default_console_loglevel */
69 EXPORT_SYMBOL_GPL(console_printk);
71 atomic_t ignore_console_lock_warning __read_mostly = ATOMIC_INIT(0);
72 EXPORT_SYMBOL(ignore_console_lock_warning);
75 * Low level drivers may need that to know if they can schedule in
76 * their unblank() callback or not. So let's export it.
79 EXPORT_SYMBOL(oops_in_progress);
82 * console_sem protects the console_drivers list, and also
83 * provides serialisation for access to the entire console
86 static DEFINE_SEMAPHORE(console_sem);
87 struct console *console_drivers;
88 EXPORT_SYMBOL_GPL(console_drivers);
91 * System may need to suppress printk message under certain
92 * circumstances, like after kernel panic happens.
94 int __read_mostly suppress_printk;
97 static struct lockdep_map console_lock_dep_map = {
98 .name = "console_lock"
102 enum devkmsg_log_bits {
103 __DEVKMSG_LOG_BIT_ON = 0,
104 __DEVKMSG_LOG_BIT_OFF,
105 __DEVKMSG_LOG_BIT_LOCK,
108 enum devkmsg_log_masks {
109 DEVKMSG_LOG_MASK_ON = BIT(__DEVKMSG_LOG_BIT_ON),
110 DEVKMSG_LOG_MASK_OFF = BIT(__DEVKMSG_LOG_BIT_OFF),
111 DEVKMSG_LOG_MASK_LOCK = BIT(__DEVKMSG_LOG_BIT_LOCK),
114 /* Keep both the 'on' and 'off' bits clear, i.e. ratelimit by default: */
115 #define DEVKMSG_LOG_MASK_DEFAULT 0
117 static unsigned int __read_mostly devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
119 static int __control_devkmsg(char *str)
126 len = str_has_prefix(str, "on");
128 devkmsg_log = DEVKMSG_LOG_MASK_ON;
132 len = str_has_prefix(str, "off");
134 devkmsg_log = DEVKMSG_LOG_MASK_OFF;
138 len = str_has_prefix(str, "ratelimit");
140 devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
147 static int __init control_devkmsg(char *str)
149 if (__control_devkmsg(str) < 0)
153 * Set sysctl string accordingly:
155 if (devkmsg_log == DEVKMSG_LOG_MASK_ON)
156 strcpy(devkmsg_log_str, "on");
157 else if (devkmsg_log == DEVKMSG_LOG_MASK_OFF)
158 strcpy(devkmsg_log_str, "off");
159 /* else "ratelimit" which is set by default. */
162 * Sysctl cannot change it anymore. The kernel command line setting of
163 * this parameter is to force the setting to be permanent throughout the
164 * runtime of the system. This is a precation measure against userspace
165 * trying to be a smarta** and attempting to change it up on us.
167 devkmsg_log |= DEVKMSG_LOG_MASK_LOCK;
171 __setup("printk.devkmsg=", control_devkmsg);
173 char devkmsg_log_str[DEVKMSG_STR_MAX_SIZE] = "ratelimit";
175 int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write,
176 void *buffer, size_t *lenp, loff_t *ppos)
178 char old_str[DEVKMSG_STR_MAX_SIZE];
183 if (devkmsg_log & DEVKMSG_LOG_MASK_LOCK)
187 strncpy(old_str, devkmsg_log_str, DEVKMSG_STR_MAX_SIZE);
190 err = proc_dostring(table, write, buffer, lenp, ppos);
195 err = __control_devkmsg(devkmsg_log_str);
198 * Do not accept an unknown string OR a known string with
201 if (err < 0 || (err + 1 != *lenp)) {
203 /* ... and restore old setting. */
205 strncpy(devkmsg_log_str, old_str, DEVKMSG_STR_MAX_SIZE);
214 /* Number of registered extended console drivers. */
215 static int nr_ext_console_drivers;
218 * Helper macros to handle lockdep when locking/unlocking console_sem. We use
219 * macros instead of functions so that _RET_IP_ contains useful information.
221 #define down_console_sem() do { \
223 mutex_acquire(&console_lock_dep_map, 0, 0, _RET_IP_);\
226 static int __down_trylock_console_sem(unsigned long ip)
232 * Here and in __up_console_sem() we need to be in safe mode,
233 * because spindump/WARN/etc from under console ->lock will
234 * deadlock in printk()->down_trylock_console_sem() otherwise.
236 printk_safe_enter_irqsave(flags);
237 lock_failed = down_trylock(&console_sem);
238 printk_safe_exit_irqrestore(flags);
242 mutex_acquire(&console_lock_dep_map, 0, 1, ip);
245 #define down_trylock_console_sem() __down_trylock_console_sem(_RET_IP_)
247 static void __up_console_sem(unsigned long ip)
251 mutex_release(&console_lock_dep_map, ip);
253 printk_safe_enter_irqsave(flags);
255 printk_safe_exit_irqrestore(flags);
257 #define up_console_sem() __up_console_sem(_RET_IP_)
260 * This is used for debugging the mess that is the VT code by
261 * keeping track if we have the console semaphore held. It's
262 * definitely not the perfect debug tool (we don't know if _WE_
263 * hold it and are racing, but it helps tracking those weird code
264 * paths in the console code where we end up in places I want
265 * locked without the console semaphore held).
267 static int console_locked, console_suspended;
270 * If exclusive_console is non-NULL then only this console is to be printed to.
272 static struct console *exclusive_console;
275 * Array of consoles built from command line options (console=)
278 #define MAX_CMDLINECONSOLES 8
280 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
282 static int preferred_console = -1;
283 static bool has_preferred_console;
284 int console_set_on_cmdline;
285 EXPORT_SYMBOL(console_set_on_cmdline);
287 /* Flag: console code may call schedule() */
288 static int console_may_schedule;
290 enum con_msg_format_flags {
291 MSG_FORMAT_DEFAULT = 0,
292 MSG_FORMAT_SYSLOG = (1 << 0),
295 static int console_msg_format = MSG_FORMAT_DEFAULT;
298 * The printk log buffer consists of a sequenced collection of records, each
299 * containing variable length message text. Every record also contains its
300 * own meta-data (@info).
302 * Every record meta-data carries the timestamp in microseconds, as well as
303 * the standard userspace syslog level and syslog facility. The usual kernel
304 * messages use LOG_KERN; userspace-injected messages always carry a matching
305 * syslog facility, by default LOG_USER. The origin of every message can be
306 * reliably determined that way.
308 * The human readable log message of a record is available in @text, the
309 * length of the message text in @text_len. The stored message is not
312 * Optionally, a record can carry a dictionary of properties (key/value
313 * pairs), to provide userspace with a machine-readable message context.
315 * Examples for well-defined, commonly used property names are:
316 * DEVICE=b12:8 device identifier
320 * +sound:card0 subsystem:devname
321 * SUBSYSTEM=pci driver-core subsystem name
323 * Valid characters in property names are [a-zA-Z0-9.-_]. Property names
324 * and values are terminated by a '\0' character.
326 * Example of record values:
327 * record.text_buf = "it's a line" (unterminated)
328 * record.info.seq = 56
329 * record.info.ts_nsec = 36863
330 * record.info.text_len = 11
331 * record.info.facility = 0 (LOG_KERN)
332 * record.info.flags = 0
333 * record.info.level = 3 (LOG_ERR)
334 * record.info.caller_id = 299 (task 299)
335 * record.info.dev_info.subsystem = "pci" (terminated)
336 * record.info.dev_info.device = "+pci:0000:00:01.0" (terminated)
338 * The 'struct printk_info' buffer must never be directly exported to
339 * userspace, it is a kernel-private implementation detail that might
340 * need to be changed in the future, when the requirements change.
342 * /dev/kmsg exports the structured data in the following line format:
343 * "<level>,<sequnum>,<timestamp>,<contflag>[,additional_values, ... ];<message text>\n"
345 * Users of the export format should ignore possible additional values
346 * separated by ',', and find the message after the ';' character.
348 * The optional key/value pairs are attached as continuation lines starting
349 * with a space character and terminated by a newline. All possible
350 * non-prinatable characters are escaped in the "\xff" notation.
353 /* syslog_lock protects syslog_* variables and write access to clear_seq. */
354 static DEFINE_MUTEX(syslog_lock);
357 DECLARE_WAIT_QUEUE_HEAD(log_wait);
358 /* All 3 protected by @syslog_lock. */
359 /* the next printk record to read by syslog(READ) or /proc/kmsg */
360 static u64 syslog_seq;
361 static size_t syslog_partial;
362 static bool syslog_time;
364 /* All 3 protected by @console_sem. */
365 /* the next printk record to write to the console */
366 static u64 console_seq;
367 static u64 exclusive_console_stop_seq;
368 static unsigned long console_dropped;
371 seqcount_latch_t latch;
376 * The next printk record to read after the last 'clear' command. There are
377 * two copies (updated with seqcount_latch) so that reads can locklessly
378 * access a valid value. Writers are synchronized by @syslog_lock.
380 static struct latched_seq clear_seq = {
381 .latch = SEQCNT_LATCH_ZERO(clear_seq.latch),
386 #ifdef CONFIG_PRINTK_CALLER
387 #define PREFIX_MAX 48
389 #define PREFIX_MAX 32
392 /* the maximum size of a formatted record (i.e. with prefix added per line) */
393 #define CONSOLE_LOG_MAX 1024
395 /* the maximum size allowed to be reserved for a record */
396 #define LOG_LINE_MAX (CONSOLE_LOG_MAX - PREFIX_MAX)
398 #define LOG_LEVEL(v) ((v) & 0x07)
399 #define LOG_FACILITY(v) ((v) >> 3 & 0xff)
402 #define LOG_ALIGN __alignof__(unsigned long)
403 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
404 #define LOG_BUF_LEN_MAX (u32)(1 << 31)
405 static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
406 static char *log_buf = __log_buf;
407 static u32 log_buf_len = __LOG_BUF_LEN;
410 * Define the average message size. This only affects the number of
411 * descriptors that will be available. Underestimating is better than
412 * overestimating (too many available descriptors is better than not enough).
414 #define PRB_AVGBITS 5 /* 32 character average length */
416 #if CONFIG_LOG_BUF_SHIFT <= PRB_AVGBITS
417 #error CONFIG_LOG_BUF_SHIFT value too small.
419 _DEFINE_PRINTKRB(printk_rb_static, CONFIG_LOG_BUF_SHIFT - PRB_AVGBITS,
420 PRB_AVGBITS, &__log_buf[0]);
422 static struct printk_ringbuffer printk_rb_dynamic;
424 static struct printk_ringbuffer *prb = &printk_rb_static;
427 * We cannot access per-CPU data (e.g. per-CPU flush irq_work) before
428 * per_cpu_areas are initialised. This variable is set to true when
429 * it's safe to access per-CPU data.
431 static bool __printk_percpu_data_ready __read_mostly;
433 bool printk_percpu_data_ready(void)
435 return __printk_percpu_data_ready;
438 /* Must be called under syslog_lock. */
439 static void latched_seq_write(struct latched_seq *ls, u64 val)
441 raw_write_seqcount_latch(&ls->latch);
443 raw_write_seqcount_latch(&ls->latch);
447 /* Can be called from any context. */
448 static u64 latched_seq_read_nolock(struct latched_seq *ls)
455 seq = raw_read_seqcount_latch(&ls->latch);
458 } while (read_seqcount_latch_retry(&ls->latch, seq));
463 /* Return log buffer address */
464 char *log_buf_addr_get(void)
469 /* Return log buffer size */
470 u32 log_buf_len_get(void)
476 * Define how much of the log buffer we could take at maximum. The value
477 * must be greater than two. Note that only half of the buffer is available
478 * when the index points to the middle.
480 #define MAX_LOG_TAKE_PART 4
481 static const char trunc_msg[] = "<truncated>";
483 static void truncate_msg(u16 *text_len, u16 *trunc_msg_len)
486 * The message should not take the whole buffer. Otherwise, it might
487 * get removed too soon.
489 u32 max_text_len = log_buf_len / MAX_LOG_TAKE_PART;
491 if (*text_len > max_text_len)
492 *text_len = max_text_len;
494 /* enable the warning message (if there is room) */
495 *trunc_msg_len = strlen(trunc_msg);
496 if (*text_len >= *trunc_msg_len)
497 *text_len -= *trunc_msg_len;
502 int dmesg_restrict = IS_ENABLED(CONFIG_SECURITY_DMESG_RESTRICT);
504 static int syslog_action_restricted(int type)
509 * Unless restricted, we allow "read all" and "get buffer size"
512 return type != SYSLOG_ACTION_READ_ALL &&
513 type != SYSLOG_ACTION_SIZE_BUFFER;
516 static int check_syslog_permissions(int type, int source)
519 * If this is from /proc/kmsg and we've already opened it, then we've
520 * already done the capabilities checks at open time.
522 if (source == SYSLOG_FROM_PROC && type != SYSLOG_ACTION_OPEN)
525 if (syslog_action_restricted(type)) {
526 if (capable(CAP_SYSLOG))
529 * For historical reasons, accept CAP_SYS_ADMIN too, with
532 if (capable(CAP_SYS_ADMIN)) {
533 pr_warn_once("%s (%d): Attempt to access syslog with "
534 "CAP_SYS_ADMIN but no CAP_SYSLOG "
536 current->comm, task_pid_nr(current));
542 return security_syslog(type);
545 static void append_char(char **pp, char *e, char c)
551 static ssize_t info_print_ext_header(char *buf, size_t size,
552 struct printk_info *info)
554 u64 ts_usec = info->ts_nsec;
556 #ifdef CONFIG_PRINTK_CALLER
557 u32 id = info->caller_id;
559 snprintf(caller, sizeof(caller), ",caller=%c%u",
560 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
565 do_div(ts_usec, 1000);
567 return scnprintf(buf, size, "%u,%llu,%llu,%c%s;",
568 (info->facility << 3) | info->level, info->seq,
569 ts_usec, info->flags & LOG_CONT ? 'c' : '-', caller);
572 static ssize_t msg_add_ext_text(char *buf, size_t size,
573 const char *text, size_t text_len,
576 char *p = buf, *e = buf + size;
579 /* escape non-printable characters */
580 for (i = 0; i < text_len; i++) {
581 unsigned char c = text[i];
583 if (c < ' ' || c >= 127 || c == '\\')
584 p += scnprintf(p, e - p, "\\x%02x", c);
586 append_char(&p, e, c);
588 append_char(&p, e, endc);
593 static ssize_t msg_add_dict_text(char *buf, size_t size,
594 const char *key, const char *val)
596 size_t val_len = strlen(val);
602 len = msg_add_ext_text(buf, size, "", 0, ' '); /* dict prefix */
603 len += msg_add_ext_text(buf + len, size - len, key, strlen(key), '=');
604 len += msg_add_ext_text(buf + len, size - len, val, val_len, '\n');
609 static ssize_t msg_print_ext_body(char *buf, size_t size,
610 char *text, size_t text_len,
611 struct dev_printk_info *dev_info)
615 len = msg_add_ext_text(buf, size, text, text_len, '\n');
620 len += msg_add_dict_text(buf + len, size - len, "SUBSYSTEM",
621 dev_info->subsystem);
622 len += msg_add_dict_text(buf + len, size - len, "DEVICE",
628 /* /dev/kmsg - userspace message inject/listen interface */
629 struct devkmsg_user {
631 struct ratelimit_state rs;
633 char buf[CONSOLE_EXT_LOG_MAX];
635 struct printk_info info;
636 char text_buf[CONSOLE_EXT_LOG_MAX];
637 struct printk_record record;
640 static __printf(3, 4) __cold
641 int devkmsg_emit(int facility, int level, const char *fmt, ...)
647 r = vprintk_emit(facility, level, NULL, fmt, args);
653 static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
656 int level = default_message_loglevel;
657 int facility = 1; /* LOG_USER */
658 struct file *file = iocb->ki_filp;
659 struct devkmsg_user *user = file->private_data;
660 size_t len = iov_iter_count(from);
663 if (!user || len > LOG_LINE_MAX)
666 /* Ignore when user logging is disabled. */
667 if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
670 /* Ratelimit when not explicitly enabled. */
671 if (!(devkmsg_log & DEVKMSG_LOG_MASK_ON)) {
672 if (!___ratelimit(&user->rs, current->comm))
676 buf = kmalloc(len+1, GFP_KERNEL);
681 if (!copy_from_iter_full(buf, len, from)) {
687 * Extract and skip the syslog prefix <[0-9]*>. Coming from userspace
688 * the decimal value represents 32bit, the lower 3 bit are the log
689 * level, the rest are the log facility.
691 * If no prefix or no userspace facility is specified, we
692 * enforce LOG_USER, to be able to reliably distinguish
693 * kernel-generated messages from userspace-injected ones.
696 if (line[0] == '<') {
700 u = simple_strtoul(line + 1, &endp, 10);
701 if (endp && endp[0] == '>') {
702 level = LOG_LEVEL(u);
703 if (LOG_FACILITY(u) != 0)
704 facility = LOG_FACILITY(u);
710 devkmsg_emit(facility, level, "%s", line);
715 static ssize_t devkmsg_read(struct file *file, char __user *buf,
716 size_t count, loff_t *ppos)
718 struct devkmsg_user *user = file->private_data;
719 struct printk_record *r = &user->record;
726 ret = mutex_lock_interruptible(&user->lock);
730 if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {
731 if (file->f_flags & O_NONBLOCK) {
736 ret = wait_event_interruptible(log_wait,
737 prb_read_valid(prb, atomic64_read(&user->seq), r));
742 if (r->info->seq != atomic64_read(&user->seq)) {
743 /* our last seen message is gone, return error and reset */
744 atomic64_set(&user->seq, r->info->seq);
749 len = info_print_ext_header(user->buf, sizeof(user->buf), r->info);
750 len += msg_print_ext_body(user->buf + len, sizeof(user->buf) - len,
751 &r->text_buf[0], r->info->text_len,
754 atomic64_set(&user->seq, r->info->seq + 1);
761 if (copy_to_user(buf, user->buf, len)) {
767 mutex_unlock(&user->lock);
772 * Be careful when modifying this function!!!
774 * Only few operations are supported because the device works only with the
775 * entire variable length messages (records). Non-standard values are
776 * returned in the other cases and has been this way for quite some time.
777 * User space applications might depend on this behavior.
779 static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
781 struct devkmsg_user *user = file->private_data;
791 /* the first record */
792 atomic64_set(&user->seq, prb_first_valid_seq(prb));
796 * The first record after the last SYSLOG_ACTION_CLEAR,
797 * like issued by 'dmesg -c'. Reading /dev/kmsg itself
798 * changes no global state, and does not clear anything.
800 atomic64_set(&user->seq, latched_seq_read_nolock(&clear_seq));
803 /* after the last record */
804 atomic64_set(&user->seq, prb_next_seq(prb));
812 static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
814 struct devkmsg_user *user = file->private_data;
815 struct printk_info info;
819 return EPOLLERR|EPOLLNVAL;
821 poll_wait(file, &log_wait, wait);
823 if (prb_read_valid_info(prb, atomic64_read(&user->seq), &info, NULL)) {
824 /* return error when data has vanished underneath us */
825 if (info.seq != atomic64_read(&user->seq))
826 ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;
828 ret = EPOLLIN|EPOLLRDNORM;
834 static int devkmsg_open(struct inode *inode, struct file *file)
836 struct devkmsg_user *user;
839 if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
842 /* write-only does not need any file context */
843 if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
844 err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
850 user = kvmalloc(sizeof(struct devkmsg_user), GFP_KERNEL);
854 ratelimit_default_init(&user->rs);
855 ratelimit_set_flags(&user->rs, RATELIMIT_MSG_ON_RELEASE);
857 mutex_init(&user->lock);
859 prb_rec_init_rd(&user->record, &user->info,
860 &user->text_buf[0], sizeof(user->text_buf));
862 atomic64_set(&user->seq, prb_first_valid_seq(prb));
864 file->private_data = user;
868 static int devkmsg_release(struct inode *inode, struct file *file)
870 struct devkmsg_user *user = file->private_data;
875 ratelimit_state_exit(&user->rs);
877 mutex_destroy(&user->lock);
882 const struct file_operations kmsg_fops = {
883 .open = devkmsg_open,
884 .read = devkmsg_read,
885 .write_iter = devkmsg_write,
886 .llseek = devkmsg_llseek,
887 .poll = devkmsg_poll,
888 .release = devkmsg_release,
891 #ifdef CONFIG_CRASH_CORE
893 * This appends the listed symbols to /proc/vmcore
895 * /proc/vmcore is used by various utilities, like crash and makedumpfile to
896 * obtain access to symbols that are otherwise very difficult to locate. These
897 * symbols are specifically used so that utilities can access and extract the
898 * dmesg log from a vmcore file after a crash.
900 void log_buf_vmcoreinfo_setup(void)
902 struct dev_printk_info *dev_info = NULL;
904 VMCOREINFO_SYMBOL(prb);
905 VMCOREINFO_SYMBOL(printk_rb_static);
906 VMCOREINFO_SYMBOL(clear_seq);
909 * Export struct size and field offsets. User space tools can
910 * parse it and detect any changes to structure down the line.
913 VMCOREINFO_STRUCT_SIZE(printk_ringbuffer);
914 VMCOREINFO_OFFSET(printk_ringbuffer, desc_ring);
915 VMCOREINFO_OFFSET(printk_ringbuffer, text_data_ring);
916 VMCOREINFO_OFFSET(printk_ringbuffer, fail);
918 VMCOREINFO_STRUCT_SIZE(prb_desc_ring);
919 VMCOREINFO_OFFSET(prb_desc_ring, count_bits);
920 VMCOREINFO_OFFSET(prb_desc_ring, descs);
921 VMCOREINFO_OFFSET(prb_desc_ring, infos);
922 VMCOREINFO_OFFSET(prb_desc_ring, head_id);
923 VMCOREINFO_OFFSET(prb_desc_ring, tail_id);
925 VMCOREINFO_STRUCT_SIZE(prb_desc);
926 VMCOREINFO_OFFSET(prb_desc, state_var);
927 VMCOREINFO_OFFSET(prb_desc, text_blk_lpos);
929 VMCOREINFO_STRUCT_SIZE(prb_data_blk_lpos);
930 VMCOREINFO_OFFSET(prb_data_blk_lpos, begin);
931 VMCOREINFO_OFFSET(prb_data_blk_lpos, next);
933 VMCOREINFO_STRUCT_SIZE(printk_info);
934 VMCOREINFO_OFFSET(printk_info, seq);
935 VMCOREINFO_OFFSET(printk_info, ts_nsec);
936 VMCOREINFO_OFFSET(printk_info, text_len);
937 VMCOREINFO_OFFSET(printk_info, caller_id);
938 VMCOREINFO_OFFSET(printk_info, dev_info);
940 VMCOREINFO_STRUCT_SIZE(dev_printk_info);
941 VMCOREINFO_OFFSET(dev_printk_info, subsystem);
942 VMCOREINFO_LENGTH(printk_info_subsystem, sizeof(dev_info->subsystem));
943 VMCOREINFO_OFFSET(dev_printk_info, device);
944 VMCOREINFO_LENGTH(printk_info_device, sizeof(dev_info->device));
946 VMCOREINFO_STRUCT_SIZE(prb_data_ring);
947 VMCOREINFO_OFFSET(prb_data_ring, size_bits);
948 VMCOREINFO_OFFSET(prb_data_ring, data);
949 VMCOREINFO_OFFSET(prb_data_ring, head_lpos);
950 VMCOREINFO_OFFSET(prb_data_ring, tail_lpos);
952 VMCOREINFO_SIZE(atomic_long_t);
953 VMCOREINFO_TYPE_OFFSET(atomic_long_t, counter);
955 VMCOREINFO_STRUCT_SIZE(latched_seq);
956 VMCOREINFO_OFFSET(latched_seq, val);
960 /* requested log_buf_len from kernel cmdline */
961 static unsigned long __initdata new_log_buf_len;
963 /* we practice scaling the ring buffer by powers of 2 */
964 static void __init log_buf_len_update(u64 size)
966 if (size > (u64)LOG_BUF_LEN_MAX) {
967 size = (u64)LOG_BUF_LEN_MAX;
968 pr_err("log_buf over 2G is not supported.\n");
972 size = roundup_pow_of_two(size);
973 if (size > log_buf_len)
974 new_log_buf_len = (unsigned long)size;
977 /* save requested log_buf_len since it's too early to process it */
978 static int __init log_buf_len_setup(char *str)
985 size = memparse(str, &str);
987 log_buf_len_update(size);
991 early_param("log_buf_len", log_buf_len_setup);
994 #define __LOG_CPU_MAX_BUF_LEN (1 << CONFIG_LOG_CPU_MAX_BUF_SHIFT)
996 static void __init log_buf_add_cpu(void)
998 unsigned int cpu_extra;
1001 * archs should set up cpu_possible_bits properly with
1002 * set_cpu_possible() after setup_arch() but just in
1003 * case lets ensure this is valid.
1005 if (num_possible_cpus() == 1)
1008 cpu_extra = (num_possible_cpus() - 1) * __LOG_CPU_MAX_BUF_LEN;
1010 /* by default this will only continue through for large > 64 CPUs */
1011 if (cpu_extra <= __LOG_BUF_LEN / 2)
1014 pr_info("log_buf_len individual max cpu contribution: %d bytes\n",
1015 __LOG_CPU_MAX_BUF_LEN);
1016 pr_info("log_buf_len total cpu_extra contributions: %d bytes\n",
1018 pr_info("log_buf_len min size: %d bytes\n", __LOG_BUF_LEN);
1020 log_buf_len_update(cpu_extra + __LOG_BUF_LEN);
1022 #else /* !CONFIG_SMP */
1023 static inline void log_buf_add_cpu(void) {}
1024 #endif /* CONFIG_SMP */
1026 static void __init set_percpu_data_ready(void)
1028 __printk_percpu_data_ready = true;
1031 static unsigned int __init add_to_rb(struct printk_ringbuffer *rb,
1032 struct printk_record *r)
1034 struct prb_reserved_entry e;
1035 struct printk_record dest_r;
1037 prb_rec_init_wr(&dest_r, r->info->text_len);
1039 if (!prb_reserve(&e, rb, &dest_r))
1042 memcpy(&dest_r.text_buf[0], &r->text_buf[0], r->info->text_len);
1043 dest_r.info->text_len = r->info->text_len;
1044 dest_r.info->facility = r->info->facility;
1045 dest_r.info->level = r->info->level;
1046 dest_r.info->flags = r->info->flags;
1047 dest_r.info->ts_nsec = r->info->ts_nsec;
1048 dest_r.info->caller_id = r->info->caller_id;
1049 memcpy(&dest_r.info->dev_info, &r->info->dev_info, sizeof(dest_r.info->dev_info));
1051 prb_final_commit(&e);
1053 return prb_record_text_space(&e);
1056 static char setup_text_buf[LOG_LINE_MAX] __initdata;
1058 void __init setup_log_buf(int early)
1060 struct printk_info *new_infos;
1061 unsigned int new_descs_count;
1062 struct prb_desc *new_descs;
1063 struct printk_info info;
1064 struct printk_record r;
1065 unsigned int text_size;
1066 size_t new_descs_size;
1067 size_t new_infos_size;
1068 unsigned long flags;
1074 * Some archs call setup_log_buf() multiple times - first is very
1075 * early, e.g. from setup_arch(), and second - when percpu_areas
1079 set_percpu_data_ready();
1081 if (log_buf != __log_buf)
1084 if (!early && !new_log_buf_len)
1087 if (!new_log_buf_len)
1090 new_descs_count = new_log_buf_len >> PRB_AVGBITS;
1091 if (new_descs_count == 0) {
1092 pr_err("new_log_buf_len: %lu too small\n", new_log_buf_len);
1096 new_log_buf = memblock_alloc(new_log_buf_len, LOG_ALIGN);
1097 if (unlikely(!new_log_buf)) {
1098 pr_err("log_buf_len: %lu text bytes not available\n",
1103 new_descs_size = new_descs_count * sizeof(struct prb_desc);
1104 new_descs = memblock_alloc(new_descs_size, LOG_ALIGN);
1105 if (unlikely(!new_descs)) {
1106 pr_err("log_buf_len: %zu desc bytes not available\n",
1108 goto err_free_log_buf;
1111 new_infos_size = new_descs_count * sizeof(struct printk_info);
1112 new_infos = memblock_alloc(new_infos_size, LOG_ALIGN);
1113 if (unlikely(!new_infos)) {
1114 pr_err("log_buf_len: %zu info bytes not available\n",
1116 goto err_free_descs;
1119 prb_rec_init_rd(&r, &info, &setup_text_buf[0], sizeof(setup_text_buf));
1121 prb_init(&printk_rb_dynamic,
1122 new_log_buf, ilog2(new_log_buf_len),
1123 new_descs, ilog2(new_descs_count),
1126 local_irq_save(flags);
1128 log_buf_len = new_log_buf_len;
1129 log_buf = new_log_buf;
1130 new_log_buf_len = 0;
1132 free = __LOG_BUF_LEN;
1133 prb_for_each_record(0, &printk_rb_static, seq, &r) {
1134 text_size = add_to_rb(&printk_rb_dynamic, &r);
1135 if (text_size > free)
1141 prb = &printk_rb_dynamic;
1143 local_irq_restore(flags);
1146 * Copy any remaining messages that might have appeared from
1147 * NMI context after copying but before switching to the
1150 prb_for_each_record(seq, &printk_rb_static, seq, &r) {
1151 text_size = add_to_rb(&printk_rb_dynamic, &r);
1152 if (text_size > free)
1158 if (seq != prb_next_seq(&printk_rb_static)) {
1159 pr_err("dropped %llu messages\n",
1160 prb_next_seq(&printk_rb_static) - seq);
1163 pr_info("log_buf_len: %u bytes\n", log_buf_len);
1164 pr_info("early log buf free: %u(%u%%)\n",
1165 free, (free * 100) / __LOG_BUF_LEN);
1169 memblock_free_ptr(new_descs, new_descs_size);
1171 memblock_free_ptr(new_log_buf, new_log_buf_len);
1174 static bool __read_mostly ignore_loglevel;
1176 static int __init ignore_loglevel_setup(char *str)
1178 ignore_loglevel = true;
1179 pr_info("debug: ignoring loglevel setting.\n");
1184 early_param("ignore_loglevel", ignore_loglevel_setup);
1185 module_param(ignore_loglevel, bool, S_IRUGO | S_IWUSR);
1186 MODULE_PARM_DESC(ignore_loglevel,
1187 "ignore loglevel setting (prints all kernel messages to the console)");
1189 static bool suppress_message_printing(int level)
1191 return (level >= console_loglevel && !ignore_loglevel);
1194 #ifdef CONFIG_BOOT_PRINTK_DELAY
1196 static int boot_delay; /* msecs delay after each printk during bootup */
1197 static unsigned long long loops_per_msec; /* based on boot_delay */
1199 static int __init boot_delay_setup(char *str)
1203 lpj = preset_lpj ? preset_lpj : 1000000; /* some guess */
1204 loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
1206 get_option(&str, &boot_delay);
1207 if (boot_delay > 10 * 1000)
1210 pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
1211 "HZ: %d, loops_per_msec: %llu\n",
1212 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
1215 early_param("boot_delay", boot_delay_setup);
1217 static void boot_delay_msec(int level)
1219 unsigned long long k;
1220 unsigned long timeout;
1222 if ((boot_delay == 0 || system_state >= SYSTEM_RUNNING)
1223 || suppress_message_printing(level)) {
1227 k = (unsigned long long)loops_per_msec * boot_delay;
1229 timeout = jiffies + msecs_to_jiffies(boot_delay);
1234 * use (volatile) jiffies to prevent
1235 * compiler reduction; loop termination via jiffies
1236 * is secondary and may or may not happen.
1238 if (time_after(jiffies, timeout))
1240 touch_nmi_watchdog();
1244 static inline void boot_delay_msec(int level)
1249 static bool printk_time = IS_ENABLED(CONFIG_PRINTK_TIME);
1250 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
1252 static size_t print_syslog(unsigned int level, char *buf)
1254 return sprintf(buf, "<%u>", level);
1257 static size_t print_time(u64 ts, char *buf)
1259 unsigned long rem_nsec = do_div(ts, 1000000000);
1261 return sprintf(buf, "[%5lu.%06lu]",
1262 (unsigned long)ts, rem_nsec / 1000);
1265 #ifdef CONFIG_PRINTK_CALLER
1266 static size_t print_caller(u32 id, char *buf)
1270 snprintf(caller, sizeof(caller), "%c%u",
1271 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
1272 return sprintf(buf, "[%6s]", caller);
1275 #define print_caller(id, buf) 0
1278 static size_t info_print_prefix(const struct printk_info *info, bool syslog,
1279 bool time, char *buf)
1284 len = print_syslog((info->facility << 3) | info->level, buf);
1287 len += print_time(info->ts_nsec, buf + len);
1289 len += print_caller(info->caller_id, buf + len);
1291 if (IS_ENABLED(CONFIG_PRINTK_CALLER) || time) {
1300 * Prepare the record for printing. The text is shifted within the given
1301 * buffer to avoid a need for another one. The following operations are
1304 * - Add prefix for each line.
1305 * - Drop truncated lines that no longer fit into the buffer.
1306 * - Add the trailing newline that has been removed in vprintk_store().
1307 * - Add a string terminator.
1309 * Since the produced string is always terminated, the maximum possible
1310 * return value is @r->text_buf_size - 1;
1312 * Return: The length of the updated/prepared text, including the added
1313 * prefixes and the newline. The terminator is not counted. The dropped
1314 * line(s) are not counted.
1316 static size_t record_print_text(struct printk_record *r, bool syslog,
1319 size_t text_len = r->info->text_len;
1320 size_t buf_size = r->text_buf_size;
1321 char *text = r->text_buf;
1322 char prefix[PREFIX_MAX];
1323 bool truncated = false;
1330 * If the message was truncated because the buffer was not large
1331 * enough, treat the available text as if it were the full text.
1333 if (text_len > buf_size)
1334 text_len = buf_size;
1336 prefix_len = info_print_prefix(r->info, syslog, time, prefix);
1339 * @text_len: bytes of unprocessed text
1340 * @line_len: bytes of current line _without_ newline
1341 * @text: pointer to beginning of current line
1342 * @len: number of bytes prepared in r->text_buf
1345 next = memchr(text, '\n', text_len);
1347 line_len = next - text;
1349 /* Drop truncated line(s). */
1352 line_len = text_len;
1356 * Truncate the text if there is not enough space to add the
1357 * prefix and a trailing newline and a terminator.
1359 if (len + prefix_len + text_len + 1 + 1 > buf_size) {
1360 /* Drop even the current line if no space. */
1361 if (len + prefix_len + line_len + 1 + 1 > buf_size)
1364 text_len = buf_size - len - prefix_len - 1 - 1;
1368 memmove(text + prefix_len, text, text_len);
1369 memcpy(text, prefix, prefix_len);
1372 * Increment the prepared length to include the text and
1373 * prefix that were just moved+copied. Also increment for the
1374 * newline at the end of this line. If this is the last line,
1375 * there is no newline, but it will be added immediately below.
1377 len += prefix_len + line_len + 1;
1378 if (text_len == line_len) {
1380 * This is the last line. Add the trailing newline
1381 * removed in vprintk_store().
1383 text[prefix_len + line_len] = '\n';
1388 * Advance beyond the added prefix and the related line with
1391 text += prefix_len + line_len + 1;
1394 * The remaining text has only decreased by the line with its
1397 * Note that @text_len can become zero. It happens when @text
1398 * ended with a newline (either due to truncation or the
1399 * original string ending with "\n\n"). The loop is correctly
1400 * repeated and (if not truncated) an empty line with a prefix
1403 text_len -= line_len + 1;
1407 * If a buffer was provided, it will be terminated. Space for the
1408 * string terminator is guaranteed to be available. The terminator is
1409 * not counted in the return value.
1412 r->text_buf[len] = 0;
1417 static size_t get_record_print_text_size(struct printk_info *info,
1418 unsigned int line_count,
1419 bool syslog, bool time)
1421 char prefix[PREFIX_MAX];
1424 prefix_len = info_print_prefix(info, syslog, time, prefix);
1427 * Each line will be preceded with a prefix. The intermediate
1428 * newlines are already within the text, but a final trailing
1429 * newline will be added.
1431 return ((prefix_len * line_count) + info->text_len + 1);
1435 * Beginning with @start_seq, find the first record where it and all following
1436 * records up to (but not including) @max_seq fit into @size.
1438 * @max_seq is simply an upper bound and does not need to exist. If the caller
1439 * does not require an upper bound, -1 can be used for @max_seq.
1441 static u64 find_first_fitting_seq(u64 start_seq, u64 max_seq, size_t size,
1442 bool syslog, bool time)
1444 struct printk_info info;
1445 unsigned int line_count;
1449 /* Determine the size of the records up to @max_seq. */
1450 prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
1451 if (info.seq >= max_seq)
1453 len += get_record_print_text_size(&info, line_count, syslog, time);
1457 * Adjust the upper bound for the next loop to avoid subtracting
1458 * lengths that were never added.
1464 * Move first record forward until length fits into the buffer. Ignore
1465 * newest messages that were not counted in the above cycle. Messages
1466 * might appear and get lost in the meantime. This is a best effort
1467 * that prevents an infinite loop that could occur with a retry.
1469 prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
1470 if (len <= size || info.seq >= max_seq)
1472 len -= get_record_print_text_size(&info, line_count, syslog, time);
1478 /* The caller is responsible for making sure @size is greater than 0. */
1479 static int syslog_print(char __user *buf, int size)
1481 struct printk_info info;
1482 struct printk_record r;
1487 text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
1491 prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
1493 mutex_lock(&syslog_lock);
1496 * Wait for the @syslog_seq record to be available. @syslog_seq may
1497 * change while waiting.
1502 mutex_unlock(&syslog_lock);
1503 len = wait_event_interruptible(log_wait, prb_read_valid(prb, seq, NULL));
1504 mutex_lock(&syslog_lock);
1508 } while (syslog_seq != seq);
1511 * Copy records that fit into the buffer. The above cycle makes sure
1512 * that the first record is always available.
1519 if (!prb_read_valid(prb, syslog_seq, &r))
1522 if (r.info->seq != syslog_seq) {
1523 /* message is gone, move to next valid one */
1524 syslog_seq = r.info->seq;
1529 * To keep reading/counting partial line consistent,
1530 * use printk_time value as of the beginning of a line.
1532 if (!syslog_partial)
1533 syslog_time = printk_time;
1535 skip = syslog_partial;
1536 n = record_print_text(&r, true, syslog_time);
1537 if (n - syslog_partial <= size) {
1538 /* message fits into buffer, move forward */
1539 syslog_seq = r.info->seq + 1;
1540 n -= syslog_partial;
1543 /* partial read(), remember position */
1545 syslog_partial += n;
1552 mutex_unlock(&syslog_lock);
1553 err = copy_to_user(buf, text + skip, n);
1554 mutex_lock(&syslog_lock);
1567 mutex_unlock(&syslog_lock);
1572 static int syslog_print_all(char __user *buf, int size, bool clear)
1574 struct printk_info info;
1575 struct printk_record r;
1581 text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
1587 * Find first record that fits, including all following records,
1588 * into the user-provided buffer for this dump.
1590 seq = find_first_fitting_seq(latched_seq_read_nolock(&clear_seq), -1,
1593 prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
1596 prb_for_each_record(seq, prb, seq, &r) {
1599 textlen = record_print_text(&r, true, time);
1601 if (len + textlen > size) {
1606 if (copy_to_user(buf + len, text, textlen))
1616 mutex_lock(&syslog_lock);
1617 latched_seq_write(&clear_seq, seq);
1618 mutex_unlock(&syslog_lock);
1625 static void syslog_clear(void)
1627 mutex_lock(&syslog_lock);
1628 latched_seq_write(&clear_seq, prb_next_seq(prb));
1629 mutex_unlock(&syslog_lock);
1632 int do_syslog(int type, char __user *buf, int len, int source)
1634 struct printk_info info;
1636 static int saved_console_loglevel = LOGLEVEL_DEFAULT;
1639 error = check_syslog_permissions(type, source);
1644 case SYSLOG_ACTION_CLOSE: /* Close log */
1646 case SYSLOG_ACTION_OPEN: /* Open log */
1648 case SYSLOG_ACTION_READ: /* Read from log */
1649 if (!buf || len < 0)
1653 if (!access_ok(buf, len))
1655 error = syslog_print(buf, len);
1657 /* Read/clear last kernel messages */
1658 case SYSLOG_ACTION_READ_CLEAR:
1661 /* Read last kernel messages */
1662 case SYSLOG_ACTION_READ_ALL:
1663 if (!buf || len < 0)
1667 if (!access_ok(buf, len))
1669 error = syslog_print_all(buf, len, clear);
1671 /* Clear ring buffer */
1672 case SYSLOG_ACTION_CLEAR:
1675 /* Disable logging to console */
1676 case SYSLOG_ACTION_CONSOLE_OFF:
1677 if (saved_console_loglevel == LOGLEVEL_DEFAULT)
1678 saved_console_loglevel = console_loglevel;
1679 console_loglevel = minimum_console_loglevel;
1681 /* Enable logging to console */
1682 case SYSLOG_ACTION_CONSOLE_ON:
1683 if (saved_console_loglevel != LOGLEVEL_DEFAULT) {
1684 console_loglevel = saved_console_loglevel;
1685 saved_console_loglevel = LOGLEVEL_DEFAULT;
1688 /* Set level of messages printed to console */
1689 case SYSLOG_ACTION_CONSOLE_LEVEL:
1690 if (len < 1 || len > 8)
1692 if (len < minimum_console_loglevel)
1693 len = minimum_console_loglevel;
1694 console_loglevel = len;
1695 /* Implicitly re-enable logging to console */
1696 saved_console_loglevel = LOGLEVEL_DEFAULT;
1698 /* Number of chars in the log buffer */
1699 case SYSLOG_ACTION_SIZE_UNREAD:
1700 mutex_lock(&syslog_lock);
1701 if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) {
1702 /* No unread messages. */
1703 mutex_unlock(&syslog_lock);
1706 if (info.seq != syslog_seq) {
1707 /* messages are gone, move to first one */
1708 syslog_seq = info.seq;
1711 if (source == SYSLOG_FROM_PROC) {
1713 * Short-cut for poll(/"proc/kmsg") which simply checks
1714 * for pending data, not the size; return the count of
1715 * records, not the length.
1717 error = prb_next_seq(prb) - syslog_seq;
1719 bool time = syslog_partial ? syslog_time : printk_time;
1720 unsigned int line_count;
1723 prb_for_each_info(syslog_seq, prb, seq, &info,
1725 error += get_record_print_text_size(&info, line_count,
1729 error -= syslog_partial;
1731 mutex_unlock(&syslog_lock);
1733 /* Size of the log buffer */
1734 case SYSLOG_ACTION_SIZE_BUFFER:
1735 error = log_buf_len;
1745 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
1747 return do_syslog(type, buf, len, SYSLOG_FROM_READER);
1751 * Special console_lock variants that help to reduce the risk of soft-lockups.
1752 * They allow to pass console_lock to another printk() call using a busy wait.
1755 #ifdef CONFIG_LOCKDEP
1756 static struct lockdep_map console_owner_dep_map = {
1757 .name = "console_owner"
1761 static DEFINE_RAW_SPINLOCK(console_owner_lock);
1762 static struct task_struct *console_owner;
1763 static bool console_waiter;
1766 * console_lock_spinning_enable - mark beginning of code where another
1767 * thread might safely busy wait
1769 * This basically converts console_lock into a spinlock. This marks
1770 * the section where the console_lock owner can not sleep, because
1771 * there may be a waiter spinning (like a spinlock). Also it must be
1772 * ready to hand over the lock at the end of the section.
1774 static void console_lock_spinning_enable(void)
1776 raw_spin_lock(&console_owner_lock);
1777 console_owner = current;
1778 raw_spin_unlock(&console_owner_lock);
1780 /* The waiter may spin on us after setting console_owner */
1781 spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
1785 * console_lock_spinning_disable_and_check - mark end of code where another
1786 * thread was able to busy wait and check if there is a waiter
1788 * This is called at the end of the section where spinning is allowed.
1789 * It has two functions. First, it is a signal that it is no longer
1790 * safe to start busy waiting for the lock. Second, it checks if
1791 * there is a busy waiter and passes the lock rights to her.
1793 * Important: Callers lose the lock if there was a busy waiter.
1794 * They must not touch items synchronized by console_lock
1797 * Return: 1 if the lock rights were passed, 0 otherwise.
1799 static int console_lock_spinning_disable_and_check(void)
1803 raw_spin_lock(&console_owner_lock);
1804 waiter = READ_ONCE(console_waiter);
1805 console_owner = NULL;
1806 raw_spin_unlock(&console_owner_lock);
1809 spin_release(&console_owner_dep_map, _THIS_IP_);
1813 /* The waiter is now free to continue */
1814 WRITE_ONCE(console_waiter, false);
1816 spin_release(&console_owner_dep_map, _THIS_IP_);
1819 * Hand off console_lock to waiter. The waiter will perform
1820 * the up(). After this, the waiter is the console_lock owner.
1822 mutex_release(&console_lock_dep_map, _THIS_IP_);
1827 * console_trylock_spinning - try to get console_lock by busy waiting
1829 * This allows to busy wait for the console_lock when the current
1830 * owner is running in specially marked sections. It means that
1831 * the current owner is running and cannot reschedule until it
1832 * is ready to lose the lock.
1834 * Return: 1 if we got the lock, 0 othrewise
1836 static int console_trylock_spinning(void)
1838 struct task_struct *owner = NULL;
1841 unsigned long flags;
1843 if (console_trylock())
1846 printk_safe_enter_irqsave(flags);
1848 raw_spin_lock(&console_owner_lock);
1849 owner = READ_ONCE(console_owner);
1850 waiter = READ_ONCE(console_waiter);
1851 if (!waiter && owner && owner != current) {
1852 WRITE_ONCE(console_waiter, true);
1855 raw_spin_unlock(&console_owner_lock);
1858 * If there is an active printk() writing to the
1859 * consoles, instead of having it write our data too,
1860 * see if we can offload that load from the active
1861 * printer, and do some printing ourselves.
1862 * Go into a spin only if there isn't already a waiter
1863 * spinning, and there is an active printer, and
1864 * that active printer isn't us (recursive printk?).
1867 printk_safe_exit_irqrestore(flags);
1871 /* We spin waiting for the owner to release us */
1872 spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
1873 /* Owner will clear console_waiter on hand off */
1874 while (READ_ONCE(console_waiter))
1876 spin_release(&console_owner_dep_map, _THIS_IP_);
1878 printk_safe_exit_irqrestore(flags);
1880 * The owner passed the console lock to us.
1881 * Since we did not spin on console lock, annotate
1882 * this as a trylock. Otherwise lockdep will
1885 mutex_acquire(&console_lock_dep_map, 0, 1, _THIS_IP_);
1891 * Call the console drivers, asking them to write out
1892 * log_buf[start] to log_buf[end - 1].
1893 * The console_lock must be held.
1895 static void call_console_drivers(const char *ext_text, size_t ext_len,
1896 const char *text, size_t len)
1898 static char dropped_text[64];
1899 size_t dropped_len = 0;
1900 struct console *con;
1902 trace_console_rcuidle(text, len);
1904 if (!console_drivers)
1907 if (console_dropped) {
1908 dropped_len = snprintf(dropped_text, sizeof(dropped_text),
1909 "** %lu printk messages dropped **\n",
1911 console_dropped = 0;
1914 for_each_console(con) {
1915 if (exclusive_console && con != exclusive_console)
1917 if (!(con->flags & CON_ENABLED))
1921 if (!cpu_online(smp_processor_id()) &&
1922 !(con->flags & CON_ANYTIME))
1924 if (con->flags & CON_EXTENDED)
1925 con->write(con, ext_text, ext_len);
1928 con->write(con, dropped_text, dropped_len);
1929 con->write(con, text, len);
1935 * Recursion is tracked separately on each CPU. If NMIs are supported, an
1936 * additional NMI context per CPU is also separately tracked. Until per-CPU
1937 * is available, a separate "early tracking" is performed.
1939 static DEFINE_PER_CPU(u8, printk_count);
1940 static u8 printk_count_early;
1941 #ifdef CONFIG_HAVE_NMI
1942 static DEFINE_PER_CPU(u8, printk_count_nmi);
1943 static u8 printk_count_nmi_early;
1947 * Recursion is limited to keep the output sane. printk() should not require
1948 * more than 1 level of recursion (allowing, for example, printk() to trigger
1949 * a WARN), but a higher value is used in case some printk-internal errors
1950 * exist, such as the ringbuffer validation checks failing.
1952 #define PRINTK_MAX_RECURSION 3
1955 * Return a pointer to the dedicated counter for the CPU+context of the
1958 static u8 *__printk_recursion_counter(void)
1960 #ifdef CONFIG_HAVE_NMI
1962 if (printk_percpu_data_ready())
1963 return this_cpu_ptr(&printk_count_nmi);
1964 return &printk_count_nmi_early;
1967 if (printk_percpu_data_ready())
1968 return this_cpu_ptr(&printk_count);
1969 return &printk_count_early;
1973 * Enter recursion tracking. Interrupts are disabled to simplify tracking.
1974 * The caller must check the boolean return value to see if the recursion is
1975 * allowed. On failure, interrupts are not disabled.
1977 * @recursion_ptr must be a variable of type (u8 *) and is the same variable
1978 * that is passed to printk_exit_irqrestore().
1980 #define printk_enter_irqsave(recursion_ptr, flags) \
1982 bool success = true; \
1984 typecheck(u8 *, recursion_ptr); \
1985 local_irq_save(flags); \
1986 (recursion_ptr) = __printk_recursion_counter(); \
1987 if (*(recursion_ptr) > PRINTK_MAX_RECURSION) { \
1988 local_irq_restore(flags); \
1991 (*(recursion_ptr))++; \
1996 /* Exit recursion tracking, restoring interrupts. */
1997 #define printk_exit_irqrestore(recursion_ptr, flags) \
1999 typecheck(u8 *, recursion_ptr); \
2000 (*(recursion_ptr))--; \
2001 local_irq_restore(flags); \
2004 int printk_delay_msec __read_mostly;
2006 static inline void printk_delay(void)
2008 if (unlikely(printk_delay_msec)) {
2009 int m = printk_delay_msec;
2013 touch_nmi_watchdog();
2018 static inline u32 printk_caller_id(void)
2020 return in_task() ? task_pid_nr(current) :
2021 0x80000000 + raw_smp_processor_id();
2025 * printk_parse_prefix - Parse level and control flags.
2027 * @text: The terminated text message.
2028 * @level: A pointer to the current level value, will be updated.
2029 * @flags: A pointer to the current printk_info flags, will be updated.
2031 * @level may be NULL if the caller is not interested in the parsed value.
2032 * Otherwise the variable pointed to by @level must be set to
2033 * LOGLEVEL_DEFAULT in order to be updated with the parsed value.
2035 * @flags may be NULL if the caller is not interested in the parsed value.
2036 * Otherwise the variable pointed to by @flags will be OR'd with the parsed
2039 * Return: The length of the parsed level and control flags.
2041 u16 printk_parse_prefix(const char *text, int *level,
2042 enum printk_info_flags *flags)
2048 kern_level = printk_get_level(text);
2052 switch (kern_level) {
2054 if (level && *level == LOGLEVEL_DEFAULT)
2055 *level = kern_level - '0';
2057 case 'c': /* KERN_CONT */
2070 static u16 printk_sprint(char *text, u16 size, int facility,
2071 enum printk_info_flags *flags, const char *fmt,
2076 text_len = vscnprintf(text, size, fmt, args);
2078 /* Mark and strip a trailing newline. */
2079 if (text_len && text[text_len - 1] == '\n') {
2081 *flags |= LOG_NEWLINE;
2084 /* Strip log level and control flags. */
2085 if (facility == 0) {
2088 prefix_len = printk_parse_prefix(text, NULL, NULL);
2090 text_len -= prefix_len;
2091 memmove(text, text + prefix_len, text_len);
2099 int vprintk_store(int facility, int level,
2100 const struct dev_printk_info *dev_info,
2101 const char *fmt, va_list args)
2103 const u32 caller_id = printk_caller_id();
2104 struct prb_reserved_entry e;
2105 enum printk_info_flags flags = 0;
2106 struct printk_record r;
2107 unsigned long irqflags;
2108 u16 trunc_msg_len = 0;
2118 * Since the duration of printk() can vary depending on the message
2119 * and state of the ringbuffer, grab the timestamp now so that it is
2120 * close to the call of printk(). This provides a more deterministic
2121 * timestamp with respect to the caller.
2123 ts_nsec = local_clock();
2125 if (!printk_enter_irqsave(recursion_ptr, irqflags))
2129 * The sprintf needs to come first since the syslog prefix might be
2130 * passed in as a parameter. An extra byte must be reserved so that
2131 * later the vscnprintf() into the reserved buffer has room for the
2132 * terminating '\0', which is not counted by vsnprintf().
2134 va_copy(args2, args);
2135 reserve_size = vsnprintf(&prefix_buf[0], sizeof(prefix_buf), fmt, args2) + 1;
2138 if (reserve_size > LOG_LINE_MAX)
2139 reserve_size = LOG_LINE_MAX;
2141 /* Extract log level or control flags. */
2143 printk_parse_prefix(&prefix_buf[0], &level, &flags);
2145 if (level == LOGLEVEL_DEFAULT)
2146 level = default_message_loglevel;
2149 flags |= LOG_NEWLINE;
2151 if (flags & LOG_CONT) {
2152 prb_rec_init_wr(&r, reserve_size);
2153 if (prb_reserve_in_last(&e, prb, &r, caller_id, LOG_LINE_MAX)) {
2154 text_len = printk_sprint(&r.text_buf[r.info->text_len], reserve_size,
2155 facility, &flags, fmt, args);
2156 r.info->text_len += text_len;
2158 if (flags & LOG_NEWLINE) {
2159 r.info->flags |= LOG_NEWLINE;
2160 prb_final_commit(&e);
2171 * Explicitly initialize the record before every prb_reserve() call.
2172 * prb_reserve_in_last() and prb_reserve() purposely invalidate the
2173 * structure when they fail.
2175 prb_rec_init_wr(&r, reserve_size);
2176 if (!prb_reserve(&e, prb, &r)) {
2177 /* truncate the message if it is too long for empty buffer */
2178 truncate_msg(&reserve_size, &trunc_msg_len);
2180 prb_rec_init_wr(&r, reserve_size + trunc_msg_len);
2181 if (!prb_reserve(&e, prb, &r))
2186 text_len = printk_sprint(&r.text_buf[0], reserve_size, facility, &flags, fmt, args);
2188 memcpy(&r.text_buf[text_len], trunc_msg, trunc_msg_len);
2189 r.info->text_len = text_len + trunc_msg_len;
2190 r.info->facility = facility;
2191 r.info->level = level & 7;
2192 r.info->flags = flags & 0x1f;
2193 r.info->ts_nsec = ts_nsec;
2194 r.info->caller_id = caller_id;
2196 memcpy(&r.info->dev_info, dev_info, sizeof(r.info->dev_info));
2198 /* A message without a trailing newline can be continued. */
2199 if (!(flags & LOG_NEWLINE))
2202 prb_final_commit(&e);
2204 ret = text_len + trunc_msg_len;
2206 printk_exit_irqrestore(recursion_ptr, irqflags);
2210 asmlinkage int vprintk_emit(int facility, int level,
2211 const struct dev_printk_info *dev_info,
2212 const char *fmt, va_list args)
2215 bool in_sched = false;
2217 /* Suppress unimportant messages after panic happens */
2218 if (unlikely(suppress_printk))
2221 if (level == LOGLEVEL_SCHED) {
2222 level = LOGLEVEL_DEFAULT;
2226 boot_delay_msec(level);
2229 printed_len = vprintk_store(facility, level, dev_info, fmt, args);
2231 /* If called from the scheduler, we can not call up(). */
2234 * Disable preemption to avoid being preempted while holding
2235 * console_sem which would prevent anyone from printing to
2240 * Try to acquire and then immediately release the console
2241 * semaphore. The release will print out buffers and wake up
2242 * /dev/kmsg and syslog() users.
2244 if (console_trylock_spinning())
2252 EXPORT_SYMBOL(vprintk_emit);
2254 int vprintk_default(const char *fmt, va_list args)
2256 return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, fmt, args);
2258 EXPORT_SYMBOL_GPL(vprintk_default);
2260 asmlinkage __visible int _printk(const char *fmt, ...)
2265 va_start(args, fmt);
2266 r = vprintk(fmt, args);
2271 EXPORT_SYMBOL(_printk);
2273 #else /* CONFIG_PRINTK */
2275 #define CONSOLE_LOG_MAX 0
2276 #define printk_time false
2278 #define prb_read_valid(rb, seq, r) false
2279 #define prb_first_valid_seq(rb) 0
2281 static u64 syslog_seq;
2282 static u64 console_seq;
2283 static u64 exclusive_console_stop_seq;
2284 static unsigned long console_dropped;
2286 static size_t record_print_text(const struct printk_record *r,
2287 bool syslog, bool time)
2291 static ssize_t info_print_ext_header(char *buf, size_t size,
2292 struct printk_info *info)
2296 static ssize_t msg_print_ext_body(char *buf, size_t size,
2297 char *text, size_t text_len,
2298 struct dev_printk_info *dev_info) { return 0; }
2299 static void console_lock_spinning_enable(void) { }
2300 static int console_lock_spinning_disable_and_check(void) { return 0; }
2301 static void call_console_drivers(const char *ext_text, size_t ext_len,
2302 const char *text, size_t len) {}
2303 static bool suppress_message_printing(int level) { return false; }
2305 #endif /* CONFIG_PRINTK */
2307 #ifdef CONFIG_EARLY_PRINTK
2308 struct console *early_console;
2310 asmlinkage __visible void early_printk(const char *fmt, ...)
2320 n = vscnprintf(buf, sizeof(buf), fmt, ap);
2323 early_console->write(early_console, buf, n);
2327 static int __add_preferred_console(char *name, int idx, char *options,
2328 char *brl_options, bool user_specified)
2330 struct console_cmdline *c;
2334 * See if this tty is not yet registered, and
2335 * if we have a slot free.
2337 for (i = 0, c = console_cmdline;
2338 i < MAX_CMDLINECONSOLES && c->name[0];
2340 if (strcmp(c->name, name) == 0 && c->index == idx) {
2342 preferred_console = i;
2344 c->user_specified = true;
2348 if (i == MAX_CMDLINECONSOLES)
2351 preferred_console = i;
2352 strlcpy(c->name, name, sizeof(c->name));
2353 c->options = options;
2354 c->user_specified = user_specified;
2355 braille_set_options(c, brl_options);
2361 static int __init console_msg_format_setup(char *str)
2363 if (!strcmp(str, "syslog"))
2364 console_msg_format = MSG_FORMAT_SYSLOG;
2365 if (!strcmp(str, "default"))
2366 console_msg_format = MSG_FORMAT_DEFAULT;
2369 __setup("console_msg_format=", console_msg_format_setup);
2372 * Set up a console. Called via do_early_param() in init/main.c
2373 * for each "console=" parameter in the boot command line.
2375 static int __init console_setup(char *str)
2377 char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for "ttyS" */
2378 char *s, *options, *brl_options = NULL;
2382 * console="" or console=null have been suggested as a way to
2383 * disable console output. Use ttynull that has been created
2384 * for exactly this purpose.
2386 if (str[0] == 0 || strcmp(str, "null") == 0) {
2387 __add_preferred_console("ttynull", 0, NULL, NULL, true);
2391 if (_braille_console_setup(&str, &brl_options))
2395 * Decode str into name, index, options.
2397 if (str[0] >= '0' && str[0] <= '9') {
2398 strcpy(buf, "ttyS");
2399 strncpy(buf + 4, str, sizeof(buf) - 5);
2401 strncpy(buf, str, sizeof(buf) - 1);
2403 buf[sizeof(buf) - 1] = 0;
2404 options = strchr(str, ',');
2408 if (!strcmp(str, "ttya"))
2409 strcpy(buf, "ttyS0");
2410 if (!strcmp(str, "ttyb"))
2411 strcpy(buf, "ttyS1");
2413 for (s = buf; *s; s++)
2414 if (isdigit(*s) || *s == ',')
2416 idx = simple_strtoul(s, NULL, 10);
2419 __add_preferred_console(buf, idx, options, brl_options, true);
2420 console_set_on_cmdline = 1;
2423 __setup("console=", console_setup);
2426 * add_preferred_console - add a device to the list of preferred consoles.
2427 * @name: device name
2428 * @idx: device index
2429 * @options: options for this console
2431 * The last preferred console added will be used for kernel messages
2432 * and stdin/out/err for init. Normally this is used by console_setup
2433 * above to handle user-supplied console arguments; however it can also
2434 * be used by arch-specific code either to override the user or more
2435 * commonly to provide a default console (ie from PROM variables) when
2436 * the user has not supplied one.
2438 int add_preferred_console(char *name, int idx, char *options)
2440 return __add_preferred_console(name, idx, options, NULL, false);
2443 bool console_suspend_enabled = true;
2444 EXPORT_SYMBOL(console_suspend_enabled);
2446 static int __init console_suspend_disable(char *str)
2448 console_suspend_enabled = false;
2451 __setup("no_console_suspend", console_suspend_disable);
2452 module_param_named(console_suspend, console_suspend_enabled,
2453 bool, S_IRUGO | S_IWUSR);
2454 MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
2455 " and hibernate operations");
2457 static bool printk_console_no_auto_verbose;
2459 void console_verbose(void)
2461 if (console_loglevel && !printk_console_no_auto_verbose)
2462 console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
2464 EXPORT_SYMBOL_GPL(console_verbose);
2466 module_param_named(console_no_auto_verbose, printk_console_no_auto_verbose, bool, 0644);
2467 MODULE_PARM_DESC(console_no_auto_verbose, "Disable console loglevel raise to highest on oops/panic/etc");
2470 * suspend_console - suspend the console subsystem
2472 * This disables printk() while we go into suspend states
2474 void suspend_console(void)
2476 if (!console_suspend_enabled)
2478 pr_info("Suspending console(s) (use no_console_suspend to debug)\n");
2480 console_suspended = 1;
2484 void resume_console(void)
2486 if (!console_suspend_enabled)
2489 console_suspended = 0;
2494 * console_cpu_notify - print deferred console messages after CPU hotplug
2497 * If printk() is called from a CPU that is not online yet, the messages
2498 * will be printed on the console only if there are CON_ANYTIME consoles.
2499 * This function is called when a new CPU comes online (or fails to come
2500 * up) or goes offline.
2502 static int console_cpu_notify(unsigned int cpu)
2504 if (!cpuhp_tasks_frozen) {
2505 /* If trylock fails, someone else is doing the printing */
2506 if (console_trylock())
2513 * console_lock - lock the console system for exclusive use.
2515 * Acquires a lock which guarantees that the caller has
2516 * exclusive access to the console system and the console_drivers list.
2518 * Can sleep, returns nothing.
2520 void console_lock(void)
2525 if (console_suspended)
2528 console_may_schedule = 1;
2530 EXPORT_SYMBOL(console_lock);
2533 * console_trylock - try to lock the console system for exclusive use.
2535 * Try to acquire a lock which guarantees that the caller has exclusive
2536 * access to the console system and the console_drivers list.
2538 * returns 1 on success, and 0 on failure to acquire the lock.
2540 int console_trylock(void)
2542 if (down_trylock_console_sem())
2544 if (console_suspended) {
2549 console_may_schedule = 0;
2552 EXPORT_SYMBOL(console_trylock);
2554 int is_console_locked(void)
2556 return console_locked;
2558 EXPORT_SYMBOL(is_console_locked);
2561 * Check if we have any console that is capable of printing while cpu is
2562 * booting or shutting down. Requires console_sem.
2564 static int have_callable_console(void)
2566 struct console *con;
2568 for_each_console(con)
2569 if ((con->flags & CON_ENABLED) &&
2570 (con->flags & CON_ANYTIME))
2577 * Can we actually use the console at this time on this cpu?
2579 * Console drivers may assume that per-cpu resources have been allocated. So
2580 * unless they're explicitly marked as being able to cope (CON_ANYTIME) don't
2581 * call them until this CPU is officially up.
2583 static inline int can_use_console(void)
2585 return cpu_online(raw_smp_processor_id()) || have_callable_console();
2589 * console_unlock - unlock the console system
2591 * Releases the console_lock which the caller holds on the console system
2592 * and the console driver list.
2594 * While the console_lock was held, console output may have been buffered
2595 * by printk(). If this is the case, console_unlock(); emits
2596 * the output prior to releasing the lock.
2598 * If there is output waiting, we wake /dev/kmsg and syslog() users.
2600 * console_unlock(); may be called from any context.
2602 void console_unlock(void)
2604 static char ext_text[CONSOLE_EXT_LOG_MAX];
2605 static char text[CONSOLE_LOG_MAX];
2606 unsigned long flags;
2607 bool do_cond_resched, retry;
2608 struct printk_info info;
2609 struct printk_record r;
2610 u64 __maybe_unused next_seq;
2612 if (console_suspended) {
2617 prb_rec_init_rd(&r, &info, text, sizeof(text));
2620 * Console drivers are called with interrupts disabled, so
2621 * @console_may_schedule should be cleared before; however, we may
2622 * end up dumping a lot of lines, for example, if called from
2623 * console registration path, and should invoke cond_resched()
2624 * between lines if allowable. Not doing so can cause a very long
2625 * scheduling stall on a slow console leading to RCU stall and
2626 * softlockup warnings which exacerbate the issue with more
2627 * messages practically incapacitating the system.
2629 * console_trylock() is not able to detect the preemptive
2630 * context reliably. Therefore the value must be stored before
2631 * and cleared after the "again" goto label.
2633 do_cond_resched = console_may_schedule;
2635 console_may_schedule = 0;
2638 * We released the console_sem lock, so we need to recheck if
2639 * cpu is online and (if not) is there at least one CON_ANYTIME
2642 if (!can_use_console()) {
2654 if (!prb_read_valid(prb, console_seq, &r))
2657 if (console_seq != r.info->seq) {
2658 console_dropped += r.info->seq - console_seq;
2659 console_seq = r.info->seq;
2662 if (suppress_message_printing(r.info->level)) {
2664 * Skip record we have buffered and already printed
2665 * directly to the console when we received it, and
2666 * record that has level above the console loglevel.
2672 /* Output to all consoles once old messages replayed. */
2673 if (unlikely(exclusive_console &&
2674 console_seq >= exclusive_console_stop_seq)) {
2675 exclusive_console = NULL;
2679 * Handle extended console text first because later
2680 * record_print_text() will modify the record buffer in-place.
2682 if (nr_ext_console_drivers) {
2683 ext_len = info_print_ext_header(ext_text,
2686 ext_len += msg_print_ext_body(ext_text + ext_len,
2687 sizeof(ext_text) - ext_len,
2692 len = record_print_text(&r,
2693 console_msg_format & MSG_FORMAT_SYSLOG,
2698 * While actively printing out messages, if another printk()
2699 * were to occur on another CPU, it may wait for this one to
2700 * finish. This task can not be preempted if there is a
2701 * waiter waiting to take over.
2703 * Interrupts are disabled because the hand over to a waiter
2704 * must not be interrupted until the hand over is completed
2705 * (@console_waiter is cleared).
2707 printk_safe_enter_irqsave(flags);
2708 console_lock_spinning_enable();
2710 stop_critical_timings(); /* don't trace print latency */
2711 call_console_drivers(ext_text, ext_len, text, len);
2712 start_critical_timings();
2714 handover = console_lock_spinning_disable_and_check();
2715 printk_safe_exit_irqrestore(flags);
2719 if (do_cond_resched)
2723 /* Get consistent value of the next-to-be-used sequence number. */
2724 next_seq = console_seq;
2730 * Someone could have filled up the buffer again, so re-check if there's
2731 * something to flush. In case we cannot trylock the console_sem again,
2732 * there's a new owner and the console_unlock() from them will do the
2733 * flush, no worries.
2735 retry = prb_read_valid(prb, next_seq, NULL);
2736 if (retry && console_trylock())
2739 EXPORT_SYMBOL(console_unlock);
2742 * console_conditional_schedule - yield the CPU if required
2744 * If the console code is currently allowed to sleep, and
2745 * if this CPU should yield the CPU to another task, do
2748 * Must be called within console_lock();.
2750 void __sched console_conditional_schedule(void)
2752 if (console_may_schedule)
2755 EXPORT_SYMBOL(console_conditional_schedule);
2757 void console_unblank(void)
2762 * console_unblank can no longer be called in interrupt context unless
2763 * oops_in_progress is set to 1..
2765 if (oops_in_progress) {
2766 if (down_trylock_console_sem() != 0)
2772 console_may_schedule = 0;
2774 if ((c->flags & CON_ENABLED) && c->unblank)
2780 * console_flush_on_panic - flush console content on panic
2781 * @mode: flush all messages in buffer or just the pending ones
2783 * Immediately output all pending messages no matter what.
2785 void console_flush_on_panic(enum con_flush_mode mode)
2788 * If someone else is holding the console lock, trylock will fail
2789 * and may_schedule may be set. Ignore and proceed to unlock so
2790 * that messages are flushed out. As this can be called from any
2791 * context and we don't want to get preempted while flushing,
2792 * ensure may_schedule is cleared.
2795 console_may_schedule = 0;
2797 if (mode == CONSOLE_REPLAY_ALL)
2798 console_seq = prb_first_valid_seq(prb);
2803 * Return the console tty driver structure and its associated index
2805 struct tty_driver *console_device(int *index)
2808 struct tty_driver *driver = NULL;
2811 for_each_console(c) {
2814 driver = c->device(c, index);
2823 * Prevent further output on the passed console device so that (for example)
2824 * serial drivers can disable console output before suspending a port, and can
2825 * re-enable output afterwards.
2827 void console_stop(struct console *console)
2830 console->flags &= ~CON_ENABLED;
2833 EXPORT_SYMBOL(console_stop);
2835 void console_start(struct console *console)
2838 console->flags |= CON_ENABLED;
2841 EXPORT_SYMBOL(console_start);
2843 static int __read_mostly keep_bootcon;
2845 static int __init keep_bootcon_setup(char *str)
2848 pr_info("debug: skip boot console de-registration.\n");
2853 early_param("keep_bootcon", keep_bootcon_setup);
2856 * This is called by register_console() to try to match
2857 * the newly registered console with any of the ones selected
2858 * by either the command line or add_preferred_console() and
2861 * Care need to be taken with consoles that are statically
2862 * enabled such as netconsole
2864 static int try_enable_new_console(struct console *newcon, bool user_specified)
2866 struct console_cmdline *c;
2869 for (i = 0, c = console_cmdline;
2870 i < MAX_CMDLINECONSOLES && c->name[0];
2872 if (c->user_specified != user_specified)
2874 if (!newcon->match ||
2875 newcon->match(newcon, c->name, c->index, c->options) != 0) {
2876 /* default matching */
2877 BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));
2878 if (strcmp(c->name, newcon->name) != 0)
2880 if (newcon->index >= 0 &&
2881 newcon->index != c->index)
2883 if (newcon->index < 0)
2884 newcon->index = c->index;
2886 if (_braille_register_console(newcon, c))
2889 if (newcon->setup &&
2890 (err = newcon->setup(newcon, c->options)) != 0)
2893 newcon->flags |= CON_ENABLED;
2894 if (i == preferred_console) {
2895 newcon->flags |= CON_CONSDEV;
2896 has_preferred_console = true;
2902 * Some consoles, such as pstore and netconsole, can be enabled even
2903 * without matching. Accept the pre-enabled consoles only when match()
2904 * and setup() had a chance to be called.
2906 if (newcon->flags & CON_ENABLED && c->user_specified == user_specified)
2913 * The console driver calls this routine during kernel initialization
2914 * to register the console printing procedure with printk() and to
2915 * print any messages that were printed by the kernel before the
2916 * console driver was initialized.
2918 * This can happen pretty early during the boot process (because of
2919 * early_printk) - sometimes before setup_arch() completes - be careful
2920 * of what kernel features are used - they may not be initialised yet.
2922 * There are two types of consoles - bootconsoles (early_printk) and
2923 * "real" consoles (everything which is not a bootconsole) which are
2924 * handled differently.
2925 * - Any number of bootconsoles can be registered at any time.
2926 * - As soon as a "real" console is registered, all bootconsoles
2927 * will be unregistered automatically.
2928 * - Once a "real" console is registered, any attempt to register a
2929 * bootconsoles will be rejected
2931 void register_console(struct console *newcon)
2933 struct console *bcon = NULL;
2936 for_each_console(bcon) {
2937 if (WARN(bcon == newcon, "console '%s%d' already registered\n",
2938 bcon->name, bcon->index))
2943 * before we register a new CON_BOOT console, make sure we don't
2944 * already have a valid console
2946 if (newcon->flags & CON_BOOT) {
2947 for_each_console(bcon) {
2948 if (!(bcon->flags & CON_BOOT)) {
2949 pr_info("Too late to register bootconsole %s%d\n",
2950 newcon->name, newcon->index);
2956 if (console_drivers && console_drivers->flags & CON_BOOT)
2957 bcon = console_drivers;
2959 if (!has_preferred_console || bcon || !console_drivers)
2960 has_preferred_console = preferred_console >= 0;
2963 * See if we want to use this console driver. If we
2964 * didn't select a console we take the first one
2965 * that registers here.
2967 if (!has_preferred_console) {
2968 if (newcon->index < 0)
2970 if (newcon->setup == NULL ||
2971 newcon->setup(newcon, NULL) == 0) {
2972 newcon->flags |= CON_ENABLED;
2973 if (newcon->device) {
2974 newcon->flags |= CON_CONSDEV;
2975 has_preferred_console = true;
2980 /* See if this console matches one we selected on the command line */
2981 err = try_enable_new_console(newcon, true);
2983 /* If not, try to match against the platform default(s) */
2985 err = try_enable_new_console(newcon, false);
2987 /* printk() messages are not printed to the Braille console. */
2988 if (err || newcon->flags & CON_BRL)
2992 * If we have a bootconsole, and are switching to a real console,
2993 * don't print everything out again, since when the boot console, and
2994 * the real console are the same physical device, it's annoying to
2995 * see the beginning boot messages twice
2997 if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
2998 newcon->flags &= ~CON_PRINTBUFFER;
3001 * Put this console in the list - keep the
3002 * preferred driver at the head of the list.
3005 if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
3006 newcon->next = console_drivers;
3007 console_drivers = newcon;
3009 newcon->next->flags &= ~CON_CONSDEV;
3010 /* Ensure this flag is always set for the head of the list */
3011 newcon->flags |= CON_CONSDEV;
3013 newcon->next = console_drivers->next;
3014 console_drivers->next = newcon;
3017 if (newcon->flags & CON_EXTENDED)
3018 nr_ext_console_drivers++;
3020 if (newcon->flags & CON_PRINTBUFFER) {
3022 * console_unlock(); will print out the buffered messages
3025 * We're about to replay the log buffer. Only do this to the
3026 * just-registered console to avoid excessive message spam to
3027 * the already-registered consoles.
3029 * Set exclusive_console with disabled interrupts to reduce
3030 * race window with eventual console_flush_on_panic() that
3031 * ignores console_lock.
3033 exclusive_console = newcon;
3034 exclusive_console_stop_seq = console_seq;
3036 /* Get a consistent copy of @syslog_seq. */
3037 mutex_lock(&syslog_lock);
3038 console_seq = syslog_seq;
3039 mutex_unlock(&syslog_lock);
3042 console_sysfs_notify();
3045 * By unregistering the bootconsoles after we enable the real console
3046 * we get the "console xxx enabled" message on all the consoles -
3047 * boot consoles, real consoles, etc - this is to ensure that end
3048 * users know there might be something in the kernel's log buffer that
3049 * went to the bootconsole (that they do not see on the real console)
3051 pr_info("%sconsole [%s%d] enabled\n",
3052 (newcon->flags & CON_BOOT) ? "boot" : "" ,
3053 newcon->name, newcon->index);
3055 ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) &&
3057 /* We need to iterate through all boot consoles, to make
3058 * sure we print everything out, before we unregister them.
3060 for_each_console(bcon)
3061 if (bcon->flags & CON_BOOT)
3062 unregister_console(bcon);
3065 EXPORT_SYMBOL(register_console);
3067 int unregister_console(struct console *console)
3069 struct console *con;
3072 pr_info("%sconsole [%s%d] disabled\n",
3073 (console->flags & CON_BOOT) ? "boot" : "" ,
3074 console->name, console->index);
3076 res = _braille_unregister_console(console);
3084 if (console_drivers == console) {
3085 console_drivers=console->next;
3088 for_each_console(con) {
3089 if (con->next == console) {
3090 con->next = console->next;
3098 goto out_disable_unlock;
3100 if (console->flags & CON_EXTENDED)
3101 nr_ext_console_drivers--;
3104 * If this isn't the last console and it has CON_CONSDEV set, we
3105 * need to set it on the next preferred console.
3107 if (console_drivers != NULL && console->flags & CON_CONSDEV)
3108 console_drivers->flags |= CON_CONSDEV;
3110 console->flags &= ~CON_ENABLED;
3112 console_sysfs_notify();
3115 res = console->exit(console);
3120 console->flags &= ~CON_ENABLED;
3125 EXPORT_SYMBOL(unregister_console);
3128 * Initialize the console device. This is called *early*, so
3129 * we can't necessarily depend on lots of kernel help here.
3130 * Just do some early initializations, and do the complex setup
3133 void __init console_init(void)
3137 initcall_entry_t *ce;
3139 /* Setup the default TTY line discipline. */
3143 * set up the console device so that later boot sequences can
3144 * inform about problems etc..
3146 ce = __con_initcall_start;
3147 trace_initcall_level("console");
3148 while (ce < __con_initcall_end) {
3149 call = initcall_from_entry(ce);
3150 trace_initcall_start(call);
3152 trace_initcall_finish(call, ret);
3158 * Some boot consoles access data that is in the init section and which will
3159 * be discarded after the initcalls have been run. To make sure that no code
3160 * will access this data, unregister the boot consoles in a late initcall.
3162 * If for some reason, such as deferred probe or the driver being a loadable
3163 * module, the real console hasn't registered yet at this point, there will
3164 * be a brief interval in which no messages are logged to the console, which
3165 * makes it difficult to diagnose problems that occur during this time.
3167 * To mitigate this problem somewhat, only unregister consoles whose memory
3168 * intersects with the init section. Note that all other boot consoles will
3169 * get unregistered when the real preferred console is registered.
3171 static int __init printk_late_init(void)
3173 struct console *con;
3176 for_each_console(con) {
3177 if (!(con->flags & CON_BOOT))
3180 /* Check addresses that might be used for enabled consoles. */
3181 if (init_section_intersects(con, sizeof(*con)) ||
3182 init_section_contains(con->write, 0) ||
3183 init_section_contains(con->read, 0) ||
3184 init_section_contains(con->device, 0) ||
3185 init_section_contains(con->unblank, 0) ||
3186 init_section_contains(con->data, 0)) {
3188 * Please, consider moving the reported consoles out
3189 * of the init section.
3191 pr_warn("bootconsole [%s%d] uses init memory and must be disabled even before the real one is ready\n",
3192 con->name, con->index);
3193 unregister_console(con);
3196 ret = cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD, "printk:dead", NULL,
3197 console_cpu_notify);
3199 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "printk:online",
3200 console_cpu_notify, NULL);
3204 late_initcall(printk_late_init);
3206 #if defined CONFIG_PRINTK
3208 * Delayed printk version, for scheduler-internal messages:
3210 #define PRINTK_PENDING_WAKEUP 0x01
3211 #define PRINTK_PENDING_OUTPUT 0x02
3213 static DEFINE_PER_CPU(int, printk_pending);
3215 static void wake_up_klogd_work_func(struct irq_work *irq_work)
3217 int pending = __this_cpu_xchg(printk_pending, 0);
3219 if (pending & PRINTK_PENDING_OUTPUT) {
3220 /* If trylock fails, someone else is doing the printing */
3221 if (console_trylock())
3225 if (pending & PRINTK_PENDING_WAKEUP)
3226 wake_up_interruptible(&log_wait);
3229 static DEFINE_PER_CPU(struct irq_work, wake_up_klogd_work) =
3230 IRQ_WORK_INIT_LAZY(wake_up_klogd_work_func);
3232 void wake_up_klogd(void)
3234 if (!printk_percpu_data_ready())
3238 if (waitqueue_active(&log_wait)) {
3239 this_cpu_or(printk_pending, PRINTK_PENDING_WAKEUP);
3240 irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
3245 void defer_console_output(void)
3247 if (!printk_percpu_data_ready())
3251 __this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
3252 irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
3256 int vprintk_deferred(const char *fmt, va_list args)
3260 r = vprintk_emit(0, LOGLEVEL_SCHED, NULL, fmt, args);
3261 defer_console_output();
3266 int _printk_deferred(const char *fmt, ...)
3271 va_start(args, fmt);
3272 r = vprintk_deferred(fmt, args);
3279 * printk rate limiting, lifted from the networking subsystem.
3281 * This enforces a rate limit: not more than 10 kernel messages
3282 * every 5s to make a denial-of-service attack impossible.
3284 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
3286 int __printk_ratelimit(const char *func)
3288 return ___ratelimit(&printk_ratelimit_state, func);
3290 EXPORT_SYMBOL(__printk_ratelimit);
3293 * printk_timed_ratelimit - caller-controlled printk ratelimiting
3294 * @caller_jiffies: pointer to caller's state
3295 * @interval_msecs: minimum interval between prints
3297 * printk_timed_ratelimit() returns true if more than @interval_msecs
3298 * milliseconds have elapsed since the last time printk_timed_ratelimit()
3301 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
3302 unsigned int interval_msecs)
3304 unsigned long elapsed = jiffies - *caller_jiffies;
3306 if (*caller_jiffies && elapsed <= msecs_to_jiffies(interval_msecs))
3309 *caller_jiffies = jiffies;
3312 EXPORT_SYMBOL(printk_timed_ratelimit);
3314 static DEFINE_SPINLOCK(dump_list_lock);
3315 static LIST_HEAD(dump_list);
3318 * kmsg_dump_register - register a kernel log dumper.
3319 * @dumper: pointer to the kmsg_dumper structure
3321 * Adds a kernel log dumper to the system. The dump callback in the
3322 * structure will be called when the kernel oopses or panics and must be
3323 * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
3325 int kmsg_dump_register(struct kmsg_dumper *dumper)
3327 unsigned long flags;
3330 /* The dump callback needs to be set */
3334 spin_lock_irqsave(&dump_list_lock, flags);
3335 /* Don't allow registering multiple times */
3336 if (!dumper->registered) {
3337 dumper->registered = 1;
3338 list_add_tail_rcu(&dumper->list, &dump_list);
3341 spin_unlock_irqrestore(&dump_list_lock, flags);
3345 EXPORT_SYMBOL_GPL(kmsg_dump_register);
3348 * kmsg_dump_unregister - unregister a kmsg dumper.
3349 * @dumper: pointer to the kmsg_dumper structure
3351 * Removes a dump device from the system. Returns zero on success and
3352 * %-EINVAL otherwise.
3354 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
3356 unsigned long flags;
3359 spin_lock_irqsave(&dump_list_lock, flags);
3360 if (dumper->registered) {
3361 dumper->registered = 0;
3362 list_del_rcu(&dumper->list);
3365 spin_unlock_irqrestore(&dump_list_lock, flags);
3370 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
3372 static bool always_kmsg_dump;
3373 module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);
3375 const char *kmsg_dump_reason_str(enum kmsg_dump_reason reason)
3378 case KMSG_DUMP_PANIC:
3380 case KMSG_DUMP_OOPS:
3382 case KMSG_DUMP_EMERG:
3384 case KMSG_DUMP_SHUTDOWN:
3390 EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
3393 * kmsg_dump - dump kernel log to kernel message dumpers.
3394 * @reason: the reason (oops, panic etc) for dumping
3396 * Call each of the registered dumper's dump() callback, which can
3397 * retrieve the kmsg records with kmsg_dump_get_line() or
3398 * kmsg_dump_get_buffer().
3400 void kmsg_dump(enum kmsg_dump_reason reason)
3402 struct kmsg_dumper *dumper;
3405 list_for_each_entry_rcu(dumper, &dump_list, list) {
3406 enum kmsg_dump_reason max_reason = dumper->max_reason;
3409 * If client has not provided a specific max_reason, default
3410 * to KMSG_DUMP_OOPS, unless always_kmsg_dump was set.
3412 if (max_reason == KMSG_DUMP_UNDEF) {
3413 max_reason = always_kmsg_dump ? KMSG_DUMP_MAX :
3416 if (reason > max_reason)
3419 /* invoke dumper which will iterate over records */
3420 dumper->dump(dumper, reason);
3426 * kmsg_dump_get_line - retrieve one kmsg log line
3427 * @iter: kmsg dump iterator
3428 * @syslog: include the "<4>" prefixes
3429 * @line: buffer to copy the line to
3430 * @size: maximum size of the buffer
3431 * @len: length of line placed into buffer
3433 * Start at the beginning of the kmsg buffer, with the oldest kmsg
3434 * record, and copy one record into the provided buffer.
3436 * Consecutive calls will return the next available record moving
3437 * towards the end of the buffer with the youngest messages.
3439 * A return value of FALSE indicates that there are no more records to
3442 bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
3443 char *line, size_t size, size_t *len)
3445 u64 min_seq = latched_seq_read_nolock(&clear_seq);
3446 struct printk_info info;
3447 unsigned int line_count;
3448 struct printk_record r;
3452 if (iter->cur_seq < min_seq)
3453 iter->cur_seq = min_seq;
3455 prb_rec_init_rd(&r, &info, line, size);
3457 /* Read text or count text lines? */
3459 if (!prb_read_valid(prb, iter->cur_seq, &r))
3461 l = record_print_text(&r, syslog, printk_time);
3463 if (!prb_read_valid_info(prb, iter->cur_seq,
3464 &info, &line_count)) {
3467 l = get_record_print_text_size(&info, line_count, syslog,
3472 iter->cur_seq = r.info->seq + 1;
3479 EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
3482 * kmsg_dump_get_buffer - copy kmsg log lines
3483 * @iter: kmsg dump iterator
3484 * @syslog: include the "<4>" prefixes
3485 * @buf: buffer to copy the line to
3486 * @size: maximum size of the buffer
3487 * @len_out: length of line placed into buffer
3489 * Start at the end of the kmsg buffer and fill the provided buffer
3490 * with as many of the *youngest* kmsg records that fit into it.
3491 * If the buffer is large enough, all available kmsg records will be
3492 * copied with a single call.
3494 * Consecutive calls will fill the buffer with the next block of
3495 * available older records, not including the earlier retrieved ones.
3497 * A return value of FALSE indicates that there are no more records to
3500 bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
3501 char *buf, size_t size, size_t *len_out)
3503 u64 min_seq = latched_seq_read_nolock(&clear_seq);
3504 struct printk_info info;
3505 struct printk_record r;
3510 bool time = printk_time;
3515 if (iter->cur_seq < min_seq)
3516 iter->cur_seq = min_seq;
3518 if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
3519 if (info.seq != iter->cur_seq) {
3520 /* messages are gone, move to first available one */
3521 iter->cur_seq = info.seq;
3526 if (iter->cur_seq >= iter->next_seq)
3530 * Find first record that fits, including all following records,
3531 * into the user-provided buffer for this dump. Pass in size-1
3532 * because this function (by way of record_print_text()) will
3533 * not write more than size-1 bytes of text into @buf.
3535 seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,
3536 size - 1, syslog, time);
3539 * Next kmsg_dump_get_buffer() invocation will dump block of
3540 * older records stored right before this one.
3544 prb_rec_init_rd(&r, &info, buf, size);
3547 prb_for_each_record(seq, prb, seq, &r) {
3548 if (r.info->seq >= iter->next_seq)
3551 len += record_print_text(&r, syslog, time);
3553 /* Adjust record to store to remaining buffer space. */
3554 prb_rec_init_rd(&r, &info, buf + len, size - len);
3557 iter->next_seq = next_seq;
3564 EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
3567 * kmsg_dump_rewind - reset the iterator
3568 * @iter: kmsg dump iterator
3570 * Reset the dumper's iterator so that kmsg_dump_get_line() and
3571 * kmsg_dump_get_buffer() can be called again and used multiple
3572 * times within the same dumper.dump() callback.
3574 void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
3576 iter->cur_seq = latched_seq_read_nolock(&clear_seq);
3577 iter->next_seq = prb_next_seq(prb);
3579 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
3584 static atomic_t printk_cpulock_owner = ATOMIC_INIT(-1);
3585 static atomic_t printk_cpulock_nested = ATOMIC_INIT(0);
3588 * __printk_wait_on_cpu_lock() - Busy wait until the printk cpu-reentrant
3589 * spinning lock is not owned by any CPU.
3591 * Context: Any context.
3593 void __printk_wait_on_cpu_lock(void)
3597 } while (atomic_read(&printk_cpulock_owner) != -1);
3599 EXPORT_SYMBOL(__printk_wait_on_cpu_lock);
3602 * __printk_cpu_trylock() - Try to acquire the printk cpu-reentrant
3605 * If no processor has the lock, the calling processor takes the lock and
3606 * becomes the owner. If the calling processor is already the owner of the
3607 * lock, this function succeeds immediately.
3609 * Context: Any context. Expects interrupts to be disabled.
3610 * Return: 1 on success, otherwise 0.
3612 int __printk_cpu_trylock(void)
3617 cpu = smp_processor_id();
3620 * Guarantee loads and stores from this CPU when it is the lock owner
3621 * are _not_ visible to the previous lock owner. This pairs with
3622 * __printk_cpu_unlock:B.
3624 * Memory barrier involvement:
3626 * If __printk_cpu_trylock:A reads from __printk_cpu_unlock:B, then
3627 * __printk_cpu_unlock:A can never read from __printk_cpu_trylock:B.
3631 * RELEASE from __printk_cpu_unlock:A to __printk_cpu_unlock:B
3632 * of the previous CPU
3634 * ACQUIRE from __printk_cpu_trylock:A to __printk_cpu_trylock:B
3637 old = atomic_cmpxchg_acquire(&printk_cpulock_owner, -1,
3638 cpu); /* LMM(__printk_cpu_trylock:A) */
3641 * This CPU is now the owner and begins loading/storing
3642 * data: LMM(__printk_cpu_trylock:B)
3646 } else if (old == cpu) {
3647 /* This CPU is already the owner. */
3648 atomic_inc(&printk_cpulock_nested);
3654 EXPORT_SYMBOL(__printk_cpu_trylock);
3657 * __printk_cpu_unlock() - Release the printk cpu-reentrant spinning lock.
3659 * The calling processor must be the owner of the lock.
3661 * Context: Any context. Expects interrupts to be disabled.
3663 void __printk_cpu_unlock(void)
3665 if (atomic_read(&printk_cpulock_nested)) {
3666 atomic_dec(&printk_cpulock_nested);
3671 * This CPU is finished loading/storing data:
3672 * LMM(__printk_cpu_unlock:A)
3676 * Guarantee loads and stores from this CPU when it was the
3677 * lock owner are visible to the next lock owner. This pairs
3678 * with __printk_cpu_trylock:A.
3680 * Memory barrier involvement:
3682 * If __printk_cpu_trylock:A reads from __printk_cpu_unlock:B,
3683 * then __printk_cpu_trylock:B reads from __printk_cpu_unlock:A.
3687 * RELEASE from __printk_cpu_unlock:A to __printk_cpu_unlock:B
3690 * ACQUIRE from __printk_cpu_trylock:A to __printk_cpu_trylock:B
3693 atomic_set_release(&printk_cpulock_owner,
3694 -1); /* LMM(__printk_cpu_unlock:B) */
3696 EXPORT_SYMBOL(__printk_cpu_unlock);
3697 #endif /* CONFIG_SMP */