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1/*
2 * linux/kernel/printk.c
3 *
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 *
6 * Modified to make sys_syslog() more flexible: added commands to
7 * return the last 4k of kernel messages, regardless of whether
8 * they've been read or not. Added option to suppress kernel printk's
9 * to the console. Added hook for sending the console messages
10 * elsewhere, in preparation for a serial line console (someday).
11 * Ted Ts'o, 2/11/93.
12 * Modified for sysctl support, 1/8/97, Chris Horn.
13 * Fixed SMP synchronization, 08/08/99, Manfred Spraul
14 * manfred@colorfullife.com
15 * Rewrote bits to get rid of console_lock
16 * 01Mar01 Andrew Morton
17 */
18
19#include <linux/kernel.h>
20#include <linux/mm.h>
21#include <linux/tty.h>
22#include <linux/tty_driver.h>
23#include <linux/console.h>
24#include <linux/init.h>
25#include <linux/jiffies.h>
26#include <linux/nmi.h>
27#include <linux/module.h>
28#include <linux/moduleparam.h>
29#include <linux/delay.h>
30#include <linux/smp.h>
31#include <linux/security.h>
32#include <linux/bootmem.h>
33#include <linux/memblock.h>
34#include <linux/syscalls.h>
35#include <linux/kexec.h>
36#include <linux/kdb.h>
37#include <linux/ratelimit.h>
38#include <linux/kmsg_dump.h>
39#include <linux/syslog.h>
40#include <linux/cpu.h>
41#include <linux/notifier.h>
42#include <linux/rculist.h>
43#include <linux/poll.h>
44#include <linux/irq_work.h>
45#include <linux/utsname.h>
46#include <linux/ctype.h>
47#include <linux/uio.h>
48
49#include <linux/uaccess.h>
50#include <asm/sections.h>
51
52#define CREATE_TRACE_POINTS
53#include <trace/events/printk.h>
54
55#include "console_cmdline.h"
56#include "braille.h"
57#include "internal.h"
58
59int console_printk[4] = {
60 CONSOLE_LOGLEVEL_DEFAULT, /* console_loglevel */
61 MESSAGE_LOGLEVEL_DEFAULT, /* default_message_loglevel */
62 CONSOLE_LOGLEVEL_MIN, /* minimum_console_loglevel */
63 CONSOLE_LOGLEVEL_DEFAULT, /* default_console_loglevel */
64};
65
66/*
67 * Low level drivers may need that to know if they can schedule in
68 * their unblank() callback or not. So let's export it.
69 */
70int oops_in_progress;
71EXPORT_SYMBOL(oops_in_progress);
72
73/*
74 * console_sem protects the console_drivers list, and also
75 * provides serialisation for access to the entire console
76 * driver system.
77 */
78static DEFINE_SEMAPHORE(console_sem);
79struct console *console_drivers;
80EXPORT_SYMBOL_GPL(console_drivers);
81
82#ifdef CONFIG_LOCKDEP
83static struct lockdep_map console_lock_dep_map = {
84 .name = "console_lock"
85};
86#endif
87
88enum devkmsg_log_bits {
89 __DEVKMSG_LOG_BIT_ON = 0,
90 __DEVKMSG_LOG_BIT_OFF,
91 __DEVKMSG_LOG_BIT_LOCK,
92};
93
94enum devkmsg_log_masks {
95 DEVKMSG_LOG_MASK_ON = BIT(__DEVKMSG_LOG_BIT_ON),
96 DEVKMSG_LOG_MASK_OFF = BIT(__DEVKMSG_LOG_BIT_OFF),
97 DEVKMSG_LOG_MASK_LOCK = BIT(__DEVKMSG_LOG_BIT_LOCK),
98};
99
100/* Keep both the 'on' and 'off' bits clear, i.e. ratelimit by default: */
101#define DEVKMSG_LOG_MASK_DEFAULT 0
102
103static unsigned int __read_mostly devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
104
105static int __control_devkmsg(char *str)
106{
107 if (!str)
108 return -EINVAL;
109
110 if (!strncmp(str, "on", 2)) {
111 devkmsg_log = DEVKMSG_LOG_MASK_ON;
112 return 2;
113 } else if (!strncmp(str, "off", 3)) {
114 devkmsg_log = DEVKMSG_LOG_MASK_OFF;
115 return 3;
116 } else if (!strncmp(str, "ratelimit", 9)) {
117 devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
118 return 9;
119 }
120 return -EINVAL;
121}
122
123static int __init control_devkmsg(char *str)
124{
125 if (__control_devkmsg(str) < 0)
126 return 1;
127
128 /*
129 * Set sysctl string accordingly:
130 */
131 if (devkmsg_log == DEVKMSG_LOG_MASK_ON) {
132 memset(devkmsg_log_str, 0, DEVKMSG_STR_MAX_SIZE);
133 strncpy(devkmsg_log_str, "on", 2);
134 } else if (devkmsg_log == DEVKMSG_LOG_MASK_OFF) {
135 memset(devkmsg_log_str, 0, DEVKMSG_STR_MAX_SIZE);
136 strncpy(devkmsg_log_str, "off", 3);
137 }
138 /* else "ratelimit" which is set by default. */
139
140 /*
141 * Sysctl cannot change it anymore. The kernel command line setting of
142 * this parameter is to force the setting to be permanent throughout the
143 * runtime of the system. This is a precation measure against userspace
144 * trying to be a smarta** and attempting to change it up on us.
145 */
146 devkmsg_log |= DEVKMSG_LOG_MASK_LOCK;
147
148 return 0;
149}
150__setup("printk.devkmsg=", control_devkmsg);
151
152char devkmsg_log_str[DEVKMSG_STR_MAX_SIZE] = "ratelimit";
153
154int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write,
155 void __user *buffer, size_t *lenp, loff_t *ppos)
156{
157 char old_str[DEVKMSG_STR_MAX_SIZE];
158 unsigned int old;
159 int err;
160
161 if (write) {
162 if (devkmsg_log & DEVKMSG_LOG_MASK_LOCK)
163 return -EINVAL;
164
165 old = devkmsg_log;
166 strncpy(old_str, devkmsg_log_str, DEVKMSG_STR_MAX_SIZE);
167 }
168
169 err = proc_dostring(table, write, buffer, lenp, ppos);
170 if (err)
171 return err;
172
173 if (write) {
174 err = __control_devkmsg(devkmsg_log_str);
175
176 /*
177 * Do not accept an unknown string OR a known string with
178 * trailing crap...
179 */
180 if (err < 0 || (err + 1 != *lenp)) {
181
182 /* ... and restore old setting. */
183 devkmsg_log = old;
184 strncpy(devkmsg_log_str, old_str, DEVKMSG_STR_MAX_SIZE);
185
186 return -EINVAL;
187 }
188 }
189
190 return 0;
191}
192
193/*
194 * Number of registered extended console drivers.
195 *
196 * If extended consoles are present, in-kernel cont reassembly is disabled
197 * and each fragment is stored as a separate log entry with proper
198 * continuation flag so that every emitted message has full metadata. This
199 * doesn't change the result for regular consoles or /proc/kmsg. For
200 * /dev/kmsg, as long as the reader concatenates messages according to
201 * consecutive continuation flags, the end result should be the same too.
202 */
203static int nr_ext_console_drivers;
204
205/*
206 * Helper macros to handle lockdep when locking/unlocking console_sem. We use
207 * macros instead of functions so that _RET_IP_ contains useful information.
208 */
209#define down_console_sem() do { \
210 down(&console_sem);\
211 mutex_acquire(&console_lock_dep_map, 0, 0, _RET_IP_);\
212} while (0)
213
214static int __down_trylock_console_sem(unsigned long ip)
215{
216 if (down_trylock(&console_sem))
217 return 1;
218 mutex_acquire(&console_lock_dep_map, 0, 1, ip);
219 return 0;
220}
221#define down_trylock_console_sem() __down_trylock_console_sem(_RET_IP_)
222
223#define up_console_sem() do { \
224 mutex_release(&console_lock_dep_map, 1, _RET_IP_);\
225 up(&console_sem);\
226} while (0)
227
228/*
229 * This is used for debugging the mess that is the VT code by
230 * keeping track if we have the console semaphore held. It's
231 * definitely not the perfect debug tool (we don't know if _WE_
232 * hold it and are racing, but it helps tracking those weird code
233 * paths in the console code where we end up in places I want
234 * locked without the console sempahore held).
235 */
236static int console_locked, console_suspended;
237
238/*
239 * If exclusive_console is non-NULL then only this console is to be printed to.
240 */
241static struct console *exclusive_console;
242
243/*
244 * Array of consoles built from command line options (console=)
245 */
246
247#define MAX_CMDLINECONSOLES 8
248
249static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
250
251static int selected_console = -1;
252static int preferred_console = -1;
253int console_set_on_cmdline;
254EXPORT_SYMBOL(console_set_on_cmdline);
255
256/* Flag: console code may call schedule() */
257static int console_may_schedule;
258
259/*
260 * The printk log buffer consists of a chain of concatenated variable
261 * length records. Every record starts with a record header, containing
262 * the overall length of the record.
263 *
264 * The heads to the first and last entry in the buffer, as well as the
265 * sequence numbers of these entries are maintained when messages are
266 * stored.
267 *
268 * If the heads indicate available messages, the length in the header
269 * tells the start next message. A length == 0 for the next message
270 * indicates a wrap-around to the beginning of the buffer.
271 *
272 * Every record carries the monotonic timestamp in microseconds, as well as
273 * the standard userspace syslog level and syslog facility. The usual
274 * kernel messages use LOG_KERN; userspace-injected messages always carry
275 * a matching syslog facility, by default LOG_USER. The origin of every
276 * message can be reliably determined that way.
277 *
278 * The human readable log message directly follows the message header. The
279 * length of the message text is stored in the header, the stored message
280 * is not terminated.
281 *
282 * Optionally, a message can carry a dictionary of properties (key/value pairs),
283 * to provide userspace with a machine-readable message context.
284 *
285 * Examples for well-defined, commonly used property names are:
286 * DEVICE=b12:8 device identifier
287 * b12:8 block dev_t
288 * c127:3 char dev_t
289 * n8 netdev ifindex
290 * +sound:card0 subsystem:devname
291 * SUBSYSTEM=pci driver-core subsystem name
292 *
293 * Valid characters in property names are [a-zA-Z0-9.-_]. The plain text value
294 * follows directly after a '=' character. Every property is terminated by
295 * a '\0' character. The last property is not terminated.
296 *
297 * Example of a message structure:
298 * 0000 ff 8f 00 00 00 00 00 00 monotonic time in nsec
299 * 0008 34 00 record is 52 bytes long
300 * 000a 0b 00 text is 11 bytes long
301 * 000c 1f 00 dictionary is 23 bytes long
302 * 000e 03 00 LOG_KERN (facility) LOG_ERR (level)
303 * 0010 69 74 27 73 20 61 20 6c "it's a l"
304 * 69 6e 65 "ine"
305 * 001b 44 45 56 49 43 "DEVIC"
306 * 45 3d 62 38 3a 32 00 44 "E=b8:2\0D"
307 * 52 49 56 45 52 3d 62 75 "RIVER=bu"
308 * 67 "g"
309 * 0032 00 00 00 padding to next message header
310 *
311 * The 'struct printk_log' buffer header must never be directly exported to
312 * userspace, it is a kernel-private implementation detail that might
313 * need to be changed in the future, when the requirements change.
314 *
315 * /dev/kmsg exports the structured data in the following line format:
316 * "<level>,<sequnum>,<timestamp>,<contflag>[,additional_values, ... ];<message text>\n"
317 *
318 * Users of the export format should ignore possible additional values
319 * separated by ',', and find the message after the ';' character.
320 *
321 * The optional key/value pairs are attached as continuation lines starting
322 * with a space character and terminated by a newline. All possible
323 * non-prinatable characters are escaped in the "\xff" notation.
324 */
325
326enum log_flags {
327 LOG_NOCONS = 1, /* already flushed, do not print to console */
328 LOG_NEWLINE = 2, /* text ended with a newline */
329 LOG_PREFIX = 4, /* text started with a prefix */
330 LOG_CONT = 8, /* text is a fragment of a continuation line */
331};
332
333struct printk_log {
334 u64 ts_nsec; /* timestamp in nanoseconds */
335 u16 len; /* length of entire record */
336 u16 text_len; /* length of text buffer */
337 u16 dict_len; /* length of dictionary buffer */
338 u8 facility; /* syslog facility */
339 u8 flags:5; /* internal record flags */
340 u8 level:3; /* syslog level */
341}
342#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
343__packed __aligned(4)
344#endif
345;
346
347/*
348 * The logbuf_lock protects kmsg buffer, indices, counters. This can be taken
349 * within the scheduler's rq lock. It must be released before calling
350 * console_unlock() or anything else that might wake up a process.
351 */
352DEFINE_RAW_SPINLOCK(logbuf_lock);
353
354#ifdef CONFIG_PRINTK
355DECLARE_WAIT_QUEUE_HEAD(log_wait);
356/* the next printk record to read by syslog(READ) or /proc/kmsg */
357static u64 syslog_seq;
358static u32 syslog_idx;
359static size_t syslog_partial;
360
361/* index and sequence number of the first record stored in the buffer */
362static u64 log_first_seq;
363static u32 log_first_idx;
364
365/* index and sequence number of the next record to store in the buffer */
366static u64 log_next_seq;
367static u32 log_next_idx;
368
369/* the next printk record to write to the console */
370static u64 console_seq;
371static u32 console_idx;
372
373/* the next printk record to read after the last 'clear' command */
374static u64 clear_seq;
375static u32 clear_idx;
376
377#define PREFIX_MAX 32
378#define LOG_LINE_MAX (1024 - PREFIX_MAX)
379
380#define LOG_LEVEL(v) ((v) & 0x07)
381#define LOG_FACILITY(v) ((v) >> 3 & 0xff)
382
383/* record buffer */
384#define LOG_ALIGN __alignof__(struct printk_log)
385#define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
386static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
387static char *log_buf = __log_buf;
388static u32 log_buf_len = __LOG_BUF_LEN;
389
390/* Return log buffer address */
391char *log_buf_addr_get(void)
392{
393 return log_buf;
394}
395
396/* Return log buffer size */
397u32 log_buf_len_get(void)
398{
399 return log_buf_len;
400}
401
402/* human readable text of the record */
403static char *log_text(const struct printk_log *msg)
404{
405 return (char *)msg + sizeof(struct printk_log);
406}
407
408/* optional key/value pair dictionary attached to the record */
409static char *log_dict(const struct printk_log *msg)
410{
411 return (char *)msg + sizeof(struct printk_log) + msg->text_len;
412}
413
414/* get record by index; idx must point to valid msg */
415static struct printk_log *log_from_idx(u32 idx)
416{
417 struct printk_log *msg = (struct printk_log *)(log_buf + idx);
418
419 /*
420 * A length == 0 record is the end of buffer marker. Wrap around and
421 * read the message at the start of the buffer.
422 */
423 if (!msg->len)
424 return (struct printk_log *)log_buf;
425 return msg;
426}
427
428/* get next record; idx must point to valid msg */
429static u32 log_next(u32 idx)
430{
431 struct printk_log *msg = (struct printk_log *)(log_buf + idx);
432
433 /* length == 0 indicates the end of the buffer; wrap */
434 /*
435 * A length == 0 record is the end of buffer marker. Wrap around and
436 * read the message at the start of the buffer as *this* one, and
437 * return the one after that.
438 */
439 if (!msg->len) {
440 msg = (struct printk_log *)log_buf;
441 return msg->len;
442 }
443 return idx + msg->len;
444}
445
446/*
447 * Check whether there is enough free space for the given message.
448 *
449 * The same values of first_idx and next_idx mean that the buffer
450 * is either empty or full.
451 *
452 * If the buffer is empty, we must respect the position of the indexes.
453 * They cannot be reset to the beginning of the buffer.
454 */
455static int logbuf_has_space(u32 msg_size, bool empty)
456{
457 u32 free;
458
459 if (log_next_idx > log_first_idx || empty)
460 free = max(log_buf_len - log_next_idx, log_first_idx);
461 else
462 free = log_first_idx - log_next_idx;
463
464 /*
465 * We need space also for an empty header that signalizes wrapping
466 * of the buffer.
467 */
468 return free >= msg_size + sizeof(struct printk_log);
469}
470
471static int log_make_free_space(u32 msg_size)
472{
473 while (log_first_seq < log_next_seq &&
474 !logbuf_has_space(msg_size, false)) {
475 /* drop old messages until we have enough contiguous space */
476 log_first_idx = log_next(log_first_idx);
477 log_first_seq++;
478 }
479
480 if (clear_seq < log_first_seq) {
481 clear_seq = log_first_seq;
482 clear_idx = log_first_idx;
483 }
484
485 /* sequence numbers are equal, so the log buffer is empty */
486 if (logbuf_has_space(msg_size, log_first_seq == log_next_seq))
487 return 0;
488
489 return -ENOMEM;
490}
491
492/* compute the message size including the padding bytes */
493static u32 msg_used_size(u16 text_len, u16 dict_len, u32 *pad_len)
494{
495 u32 size;
496
497 size = sizeof(struct printk_log) + text_len + dict_len;
498 *pad_len = (-size) & (LOG_ALIGN - 1);
499 size += *pad_len;
500
501 return size;
502}
503
504/*
505 * Define how much of the log buffer we could take at maximum. The value
506 * must be greater than two. Note that only half of the buffer is available
507 * when the index points to the middle.
508 */
509#define MAX_LOG_TAKE_PART 4
510static const char trunc_msg[] = "<truncated>";
511
512static u32 truncate_msg(u16 *text_len, u16 *trunc_msg_len,
513 u16 *dict_len, u32 *pad_len)
514{
515 /*
516 * The message should not take the whole buffer. Otherwise, it might
517 * get removed too soon.
518 */
519 u32 max_text_len = log_buf_len / MAX_LOG_TAKE_PART;
520 if (*text_len > max_text_len)
521 *text_len = max_text_len;
522 /* enable the warning message */
523 *trunc_msg_len = strlen(trunc_msg);
524 /* disable the "dict" completely */
525 *dict_len = 0;
526 /* compute the size again, count also the warning message */
527 return msg_used_size(*text_len + *trunc_msg_len, 0, pad_len);
528}
529
530/* insert record into the buffer, discard old ones, update heads */
531static int log_store(int facility, int level,
532 enum log_flags flags, u64 ts_nsec,
533 const char *dict, u16 dict_len,
534 const char *text, u16 text_len)
535{
536 struct printk_log *msg;
537 u32 size, pad_len;
538 u16 trunc_msg_len = 0;
539
540 /* number of '\0' padding bytes to next message */
541 size = msg_used_size(text_len, dict_len, &pad_len);
542
543 if (log_make_free_space(size)) {
544 /* truncate the message if it is too long for empty buffer */
545 size = truncate_msg(&text_len, &trunc_msg_len,
546 &dict_len, &pad_len);
547 /* survive when the log buffer is too small for trunc_msg */
548 if (log_make_free_space(size))
549 return 0;
550 }
551
552 if (log_next_idx + size + sizeof(struct printk_log) > log_buf_len) {
553 /*
554 * This message + an additional empty header does not fit
555 * at the end of the buffer. Add an empty header with len == 0
556 * to signify a wrap around.
557 */
558 memset(log_buf + log_next_idx, 0, sizeof(struct printk_log));
559 log_next_idx = 0;
560 }
561
562 /* fill message */
563 msg = (struct printk_log *)(log_buf + log_next_idx);
564 memcpy(log_text(msg), text, text_len);
565 msg->text_len = text_len;
566 if (trunc_msg_len) {
567 memcpy(log_text(msg) + text_len, trunc_msg, trunc_msg_len);
568 msg->text_len += trunc_msg_len;
569 }
570 memcpy(log_dict(msg), dict, dict_len);
571 msg->dict_len = dict_len;
572 msg->facility = facility;
573 msg->level = level & 7;
574 msg->flags = flags & 0x1f;
575 if (ts_nsec > 0)
576 msg->ts_nsec = ts_nsec;
577 else
578 msg->ts_nsec = local_clock();
579 memset(log_dict(msg) + dict_len, 0, pad_len);
580 msg->len = size;
581
582 /* insert message */
583 log_next_idx += msg->len;
584 log_next_seq++;
585
586 return msg->text_len;
587}
588
589int dmesg_restrict = IS_ENABLED(CONFIG_SECURITY_DMESG_RESTRICT);
590
591static int syslog_action_restricted(int type)
592{
593 if (dmesg_restrict)
594 return 1;
595 /*
596 * Unless restricted, we allow "read all" and "get buffer size"
597 * for everybody.
598 */
599 return type != SYSLOG_ACTION_READ_ALL &&
600 type != SYSLOG_ACTION_SIZE_BUFFER;
601}
602
603int check_syslog_permissions(int type, int source)
604{
605 /*
606 * If this is from /proc/kmsg and we've already opened it, then we've
607 * already done the capabilities checks at open time.
608 */
609 if (source == SYSLOG_FROM_PROC && type != SYSLOG_ACTION_OPEN)
610 goto ok;
611
612 if (syslog_action_restricted(type)) {
613 if (capable(CAP_SYSLOG))
614 goto ok;
615 /*
616 * For historical reasons, accept CAP_SYS_ADMIN too, with
617 * a warning.
618 */
619 if (capable(CAP_SYS_ADMIN)) {
620 pr_warn_once("%s (%d): Attempt to access syslog with "
621 "CAP_SYS_ADMIN but no CAP_SYSLOG "
622 "(deprecated).\n",
623 current->comm, task_pid_nr(current));
624 goto ok;
625 }
626 return -EPERM;
627 }
628ok:
629 return security_syslog(type);
630}
631EXPORT_SYMBOL_GPL(check_syslog_permissions);
632
633static void append_char(char **pp, char *e, char c)
634{
635 if (*pp < e)
636 *(*pp)++ = c;
637}
638
639static ssize_t msg_print_ext_header(char *buf, size_t size,
640 struct printk_log *msg, u64 seq)
641{
642 u64 ts_usec = msg->ts_nsec;
643
644 do_div(ts_usec, 1000);
645
646 return scnprintf(buf, size, "%u,%llu,%llu,%c;",
647 (msg->facility << 3) | msg->level, seq, ts_usec,
648 msg->flags & LOG_CONT ? 'c' : '-');
649}
650
651static ssize_t msg_print_ext_body(char *buf, size_t size,
652 char *dict, size_t dict_len,
653 char *text, size_t text_len)
654{
655 char *p = buf, *e = buf + size;
656 size_t i;
657
658 /* escape non-printable characters */
659 for (i = 0; i < text_len; i++) {
660 unsigned char c = text[i];
661
662 if (c < ' ' || c >= 127 || c == '\\')
663 p += scnprintf(p, e - p, "\\x%02x", c);
664 else
665 append_char(&p, e, c);
666 }
667 append_char(&p, e, '\n');
668
669 if (dict_len) {
670 bool line = true;
671
672 for (i = 0; i < dict_len; i++) {
673 unsigned char c = dict[i];
674
675 if (line) {
676 append_char(&p, e, ' ');
677 line = false;
678 }
679
680 if (c == '\0') {
681 append_char(&p, e, '\n');
682 line = true;
683 continue;
684 }
685
686 if (c < ' ' || c >= 127 || c == '\\') {
687 p += scnprintf(p, e - p, "\\x%02x", c);
688 continue;
689 }
690
691 append_char(&p, e, c);
692 }
693 append_char(&p, e, '\n');
694 }
695
696 return p - buf;
697}
698
699/* /dev/kmsg - userspace message inject/listen interface */
700struct devkmsg_user {
701 u64 seq;
702 u32 idx;
703 struct ratelimit_state rs;
704 struct mutex lock;
705 char buf[CONSOLE_EXT_LOG_MAX];
706};
707
708static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
709{
710 char *buf, *line;
711 int level = default_message_loglevel;
712 int facility = 1; /* LOG_USER */
713 struct file *file = iocb->ki_filp;
714 struct devkmsg_user *user = file->private_data;
715 size_t len = iov_iter_count(from);
716 ssize_t ret = len;
717
718 if (!user || len > LOG_LINE_MAX)
719 return -EINVAL;
720
721 /* Ignore when user logging is disabled. */
722 if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
723 return len;
724
725 /* Ratelimit when not explicitly enabled. */
726 if (!(devkmsg_log & DEVKMSG_LOG_MASK_ON)) {
727 if (!___ratelimit(&user->rs, current->comm))
728 return ret;
729 }
730
731 buf = kmalloc(len+1, GFP_KERNEL);
732 if (buf == NULL)
733 return -ENOMEM;
734
735 buf[len] = '\0';
736 if (!copy_from_iter_full(buf, len, from)) {
737 kfree(buf);
738 return -EFAULT;
739 }
740
741 /*
742 * Extract and skip the syslog prefix <[0-9]*>. Coming from userspace
743 * the decimal value represents 32bit, the lower 3 bit are the log
744 * level, the rest are the log facility.
745 *
746 * If no prefix or no userspace facility is specified, we
747 * enforce LOG_USER, to be able to reliably distinguish
748 * kernel-generated messages from userspace-injected ones.
749 */
750 line = buf;
751 if (line[0] == '<') {
752 char *endp = NULL;
753 unsigned int u;
754
755 u = simple_strtoul(line + 1, &endp, 10);
756 if (endp && endp[0] == '>') {
757 level = LOG_LEVEL(u);
758 if (LOG_FACILITY(u) != 0)
759 facility = LOG_FACILITY(u);
760 endp++;
761 len -= endp - line;
762 line = endp;
763 }
764 }
765
766 printk_emit(facility, level, NULL, 0, "%s", line);
767 kfree(buf);
768 return ret;
769}
770
771static ssize_t devkmsg_read(struct file *file, char __user *buf,
772 size_t count, loff_t *ppos)
773{
774 struct devkmsg_user *user = file->private_data;
775 struct printk_log *msg;
776 size_t len;
777 ssize_t ret;
778
779 if (!user)
780 return -EBADF;
781
782 ret = mutex_lock_interruptible(&user->lock);
783 if (ret)
784 return ret;
785 raw_spin_lock_irq(&logbuf_lock);
786 while (user->seq == log_next_seq) {
787 if (file->f_flags & O_NONBLOCK) {
788 ret = -EAGAIN;
789 raw_spin_unlock_irq(&logbuf_lock);
790 goto out;
791 }
792
793 raw_spin_unlock_irq(&logbuf_lock);
794 ret = wait_event_interruptible(log_wait,
795 user->seq != log_next_seq);
796 if (ret)
797 goto out;
798 raw_spin_lock_irq(&logbuf_lock);
799 }
800
801 if (user->seq < log_first_seq) {
802 /* our last seen message is gone, return error and reset */
803 user->idx = log_first_idx;
804 user->seq = log_first_seq;
805 ret = -EPIPE;
806 raw_spin_unlock_irq(&logbuf_lock);
807 goto out;
808 }
809
810 msg = log_from_idx(user->idx);
811 len = msg_print_ext_header(user->buf, sizeof(user->buf),
812 msg, user->seq);
813 len += msg_print_ext_body(user->buf + len, sizeof(user->buf) - len,
814 log_dict(msg), msg->dict_len,
815 log_text(msg), msg->text_len);
816
817 user->idx = log_next(user->idx);
818 user->seq++;
819 raw_spin_unlock_irq(&logbuf_lock);
820
821 if (len > count) {
822 ret = -EINVAL;
823 goto out;
824 }
825
826 if (copy_to_user(buf, user->buf, len)) {
827 ret = -EFAULT;
828 goto out;
829 }
830 ret = len;
831out:
832 mutex_unlock(&user->lock);
833 return ret;
834}
835
836static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
837{
838 struct devkmsg_user *user = file->private_data;
839 loff_t ret = 0;
840
841 if (!user)
842 return -EBADF;
843 if (offset)
844 return -ESPIPE;
845
846 raw_spin_lock_irq(&logbuf_lock);
847 switch (whence) {
848 case SEEK_SET:
849 /* the first record */
850 user->idx = log_first_idx;
851 user->seq = log_first_seq;
852 break;
853 case SEEK_DATA:
854 /*
855 * The first record after the last SYSLOG_ACTION_CLEAR,
856 * like issued by 'dmesg -c'. Reading /dev/kmsg itself
857 * changes no global state, and does not clear anything.
858 */
859 user->idx = clear_idx;
860 user->seq = clear_seq;
861 break;
862 case SEEK_END:
863 /* after the last record */
864 user->idx = log_next_idx;
865 user->seq = log_next_seq;
866 break;
867 default:
868 ret = -EINVAL;
869 }
870 raw_spin_unlock_irq(&logbuf_lock);
871 return ret;
872}
873
874static unsigned int devkmsg_poll(struct file *file, poll_table *wait)
875{
876 struct devkmsg_user *user = file->private_data;
877 int ret = 0;
878
879 if (!user)
880 return POLLERR|POLLNVAL;
881
882 poll_wait(file, &log_wait, wait);
883
884 raw_spin_lock_irq(&logbuf_lock);
885 if (user->seq < log_next_seq) {
886 /* return error when data has vanished underneath us */
887 if (user->seq < log_first_seq)
888 ret = POLLIN|POLLRDNORM|POLLERR|POLLPRI;
889 else
890 ret = POLLIN|POLLRDNORM;
891 }
892 raw_spin_unlock_irq(&logbuf_lock);
893
894 return ret;
895}
896
897static int devkmsg_open(struct inode *inode, struct file *file)
898{
899 struct devkmsg_user *user;
900 int err;
901
902 if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
903 return -EPERM;
904
905 /* write-only does not need any file context */
906 if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
907 err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
908 SYSLOG_FROM_READER);
909 if (err)
910 return err;
911 }
912
913 user = kmalloc(sizeof(struct devkmsg_user), GFP_KERNEL);
914 if (!user)
915 return -ENOMEM;
916
917 ratelimit_default_init(&user->rs);
918 ratelimit_set_flags(&user->rs, RATELIMIT_MSG_ON_RELEASE);
919
920 mutex_init(&user->lock);
921
922 raw_spin_lock_irq(&logbuf_lock);
923 user->idx = log_first_idx;
924 user->seq = log_first_seq;
925 raw_spin_unlock_irq(&logbuf_lock);
926
927 file->private_data = user;
928 return 0;
929}
930
931static int devkmsg_release(struct inode *inode, struct file *file)
932{
933 struct devkmsg_user *user = file->private_data;
934
935 if (!user)
936 return 0;
937
938 ratelimit_state_exit(&user->rs);
939
940 mutex_destroy(&user->lock);
941 kfree(user);
942 return 0;
943}
944
945const struct file_operations kmsg_fops = {
946 .open = devkmsg_open,
947 .read = devkmsg_read,
948 .write_iter = devkmsg_write,
949 .llseek = devkmsg_llseek,
950 .poll = devkmsg_poll,
951 .release = devkmsg_release,
952};
953
954#ifdef CONFIG_KEXEC_CORE
955/*
956 * This appends the listed symbols to /proc/vmcore
957 *
958 * /proc/vmcore is used by various utilities, like crash and makedumpfile to
959 * obtain access to symbols that are otherwise very difficult to locate. These
960 * symbols are specifically used so that utilities can access and extract the
961 * dmesg log from a vmcore file after a crash.
962 */
963void log_buf_kexec_setup(void)
964{
965 VMCOREINFO_SYMBOL(log_buf);
966 VMCOREINFO_SYMBOL(log_buf_len);
967 VMCOREINFO_SYMBOL(log_first_idx);
968 VMCOREINFO_SYMBOL(clear_idx);
969 VMCOREINFO_SYMBOL(log_next_idx);
970 /*
971 * Export struct printk_log size and field offsets. User space tools can
972 * parse it and detect any changes to structure down the line.
973 */
974 VMCOREINFO_STRUCT_SIZE(printk_log);
975 VMCOREINFO_OFFSET(printk_log, ts_nsec);
976 VMCOREINFO_OFFSET(printk_log, len);
977 VMCOREINFO_OFFSET(printk_log, text_len);
978 VMCOREINFO_OFFSET(printk_log, dict_len);
979}
980#endif
981
982/* requested log_buf_len from kernel cmdline */
983static unsigned long __initdata new_log_buf_len;
984
985/* we practice scaling the ring buffer by powers of 2 */
986static void __init log_buf_len_update(unsigned size)
987{
988 if (size)
989 size = roundup_pow_of_two(size);
990 if (size > log_buf_len)
991 new_log_buf_len = size;
992}
993
994/* save requested log_buf_len since it's too early to process it */
995static int __init log_buf_len_setup(char *str)
996{
997 unsigned size = memparse(str, &str);
998
999 log_buf_len_update(size);
1000
1001 return 0;
1002}
1003early_param("log_buf_len", log_buf_len_setup);
1004
1005#ifdef CONFIG_SMP
1006#define __LOG_CPU_MAX_BUF_LEN (1 << CONFIG_LOG_CPU_MAX_BUF_SHIFT)
1007
1008static void __init log_buf_add_cpu(void)
1009{
1010 unsigned int cpu_extra;
1011
1012 /*
1013 * archs should set up cpu_possible_bits properly with
1014 * set_cpu_possible() after setup_arch() but just in
1015 * case lets ensure this is valid.
1016 */
1017 if (num_possible_cpus() == 1)
1018 return;
1019
1020 cpu_extra = (num_possible_cpus() - 1) * __LOG_CPU_MAX_BUF_LEN;
1021
1022 /* by default this will only continue through for large > 64 CPUs */
1023 if (cpu_extra <= __LOG_BUF_LEN / 2)
1024 return;
1025
1026 pr_info("log_buf_len individual max cpu contribution: %d bytes\n",
1027 __LOG_CPU_MAX_BUF_LEN);
1028 pr_info("log_buf_len total cpu_extra contributions: %d bytes\n",
1029 cpu_extra);
1030 pr_info("log_buf_len min size: %d bytes\n", __LOG_BUF_LEN);
1031
1032 log_buf_len_update(cpu_extra + __LOG_BUF_LEN);
1033}
1034#else /* !CONFIG_SMP */
1035static inline void log_buf_add_cpu(void) {}
1036#endif /* CONFIG_SMP */
1037
1038void __init setup_log_buf(int early)
1039{
1040 unsigned long flags;
1041 char *new_log_buf;
1042 int free;
1043
1044 if (log_buf != __log_buf)
1045 return;
1046
1047 if (!early && !new_log_buf_len)
1048 log_buf_add_cpu();
1049
1050 if (!new_log_buf_len)
1051 return;
1052
1053 if (early) {
1054 new_log_buf =
1055 memblock_virt_alloc(new_log_buf_len, LOG_ALIGN);
1056 } else {
1057 new_log_buf = memblock_virt_alloc_nopanic(new_log_buf_len,
1058 LOG_ALIGN);
1059 }
1060
1061 if (unlikely(!new_log_buf)) {
1062 pr_err("log_buf_len: %ld bytes not available\n",
1063 new_log_buf_len);
1064 return;
1065 }
1066
1067 raw_spin_lock_irqsave(&logbuf_lock, flags);
1068 log_buf_len = new_log_buf_len;
1069 log_buf = new_log_buf;
1070 new_log_buf_len = 0;
1071 free = __LOG_BUF_LEN - log_next_idx;
1072 memcpy(log_buf, __log_buf, __LOG_BUF_LEN);
1073 raw_spin_unlock_irqrestore(&logbuf_lock, flags);
1074
1075 pr_info("log_buf_len: %d bytes\n", log_buf_len);
1076 pr_info("early log buf free: %d(%d%%)\n",
1077 free, (free * 100) / __LOG_BUF_LEN);
1078}
1079
1080static bool __read_mostly ignore_loglevel;
1081
1082static int __init ignore_loglevel_setup(char *str)
1083{
1084 ignore_loglevel = true;
1085 pr_info("debug: ignoring loglevel setting.\n");
1086
1087 return 0;
1088}
1089
1090early_param("ignore_loglevel", ignore_loglevel_setup);
1091module_param(ignore_loglevel, bool, S_IRUGO | S_IWUSR);
1092MODULE_PARM_DESC(ignore_loglevel,
1093 "ignore loglevel setting (prints all kernel messages to the console)");
1094
1095static bool suppress_message_printing(int level)
1096{
1097 return (level >= console_loglevel && !ignore_loglevel);
1098}
1099
1100#ifdef CONFIG_BOOT_PRINTK_DELAY
1101
1102static int boot_delay; /* msecs delay after each printk during bootup */
1103static unsigned long long loops_per_msec; /* based on boot_delay */
1104
1105static int __init boot_delay_setup(char *str)
1106{
1107 unsigned long lpj;
1108
1109 lpj = preset_lpj ? preset_lpj : 1000000; /* some guess */
1110 loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
1111
1112 get_option(&str, &boot_delay);
1113 if (boot_delay > 10 * 1000)
1114 boot_delay = 0;
1115
1116 pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
1117 "HZ: %d, loops_per_msec: %llu\n",
1118 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
1119 return 0;
1120}
1121early_param("boot_delay", boot_delay_setup);
1122
1123static void boot_delay_msec(int level)
1124{
1125 unsigned long long k;
1126 unsigned long timeout;
1127
1128 if ((boot_delay == 0 || system_state != SYSTEM_BOOTING)
1129 || suppress_message_printing(level)) {
1130 return;
1131 }
1132
1133 k = (unsigned long long)loops_per_msec * boot_delay;
1134
1135 timeout = jiffies + msecs_to_jiffies(boot_delay);
1136 while (k) {
1137 k--;
1138 cpu_relax();
1139 /*
1140 * use (volatile) jiffies to prevent
1141 * compiler reduction; loop termination via jiffies
1142 * is secondary and may or may not happen.
1143 */
1144 if (time_after(jiffies, timeout))
1145 break;
1146 touch_nmi_watchdog();
1147 }
1148}
1149#else
1150static inline void boot_delay_msec(int level)
1151{
1152}
1153#endif
1154
1155static bool printk_time = IS_ENABLED(CONFIG_PRINTK_TIME);
1156module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
1157
1158static size_t print_time(u64 ts, char *buf)
1159{
1160 unsigned long rem_nsec;
1161
1162 if (!printk_time)
1163 return 0;
1164
1165 rem_nsec = do_div(ts, 1000000000);
1166
1167 if (!buf)
1168 return snprintf(NULL, 0, "[%5lu.000000] ", (unsigned long)ts);
1169
1170 return sprintf(buf, "[%5lu.%06lu] ",
1171 (unsigned long)ts, rem_nsec / 1000);
1172}
1173
1174static size_t print_prefix(const struct printk_log *msg, bool syslog, char *buf)
1175{
1176 size_t len = 0;
1177 unsigned int prefix = (msg->facility << 3) | msg->level;
1178
1179 if (syslog) {
1180 if (buf) {
1181 len += sprintf(buf, "<%u>", prefix);
1182 } else {
1183 len += 3;
1184 if (prefix > 999)
1185 len += 3;
1186 else if (prefix > 99)
1187 len += 2;
1188 else if (prefix > 9)
1189 len++;
1190 }
1191 }
1192
1193 len += print_time(msg->ts_nsec, buf ? buf + len : NULL);
1194 return len;
1195}
1196
1197static size_t msg_print_text(const struct printk_log *msg, bool syslog, char *buf, size_t size)
1198{
1199 const char *text = log_text(msg);
1200 size_t text_size = msg->text_len;
1201 size_t len = 0;
1202
1203 do {
1204 const char *next = memchr(text, '\n', text_size);
1205 size_t text_len;
1206
1207 if (next) {
1208 text_len = next - text;
1209 next++;
1210 text_size -= next - text;
1211 } else {
1212 text_len = text_size;
1213 }
1214
1215 if (buf) {
1216 if (print_prefix(msg, syslog, NULL) +
1217 text_len + 1 >= size - len)
1218 break;
1219
1220 len += print_prefix(msg, syslog, buf + len);
1221 memcpy(buf + len, text, text_len);
1222 len += text_len;
1223 buf[len++] = '\n';
1224 } else {
1225 /* SYSLOG_ACTION_* buffer size only calculation */
1226 len += print_prefix(msg, syslog, NULL);
1227 len += text_len;
1228 len++;
1229 }
1230
1231 text = next;
1232 } while (text);
1233
1234 return len;
1235}
1236
1237static int syslog_print(char __user *buf, int size)
1238{
1239 char *text;
1240 struct printk_log *msg;
1241 int len = 0;
1242
1243 text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
1244 if (!text)
1245 return -ENOMEM;
1246
1247 while (size > 0) {
1248 size_t n;
1249 size_t skip;
1250
1251 raw_spin_lock_irq(&logbuf_lock);
1252 if (syslog_seq < log_first_seq) {
1253 /* messages are gone, move to first one */
1254 syslog_seq = log_first_seq;
1255 syslog_idx = log_first_idx;
1256 syslog_partial = 0;
1257 }
1258 if (syslog_seq == log_next_seq) {
1259 raw_spin_unlock_irq(&logbuf_lock);
1260 break;
1261 }
1262
1263 skip = syslog_partial;
1264 msg = log_from_idx(syslog_idx);
1265 n = msg_print_text(msg, true, text, LOG_LINE_MAX + PREFIX_MAX);
1266 if (n - syslog_partial <= size) {
1267 /* message fits into buffer, move forward */
1268 syslog_idx = log_next(syslog_idx);
1269 syslog_seq++;
1270 n -= syslog_partial;
1271 syslog_partial = 0;
1272 } else if (!len){
1273 /* partial read(), remember position */
1274 n = size;
1275 syslog_partial += n;
1276 } else
1277 n = 0;
1278 raw_spin_unlock_irq(&logbuf_lock);
1279
1280 if (!n)
1281 break;
1282
1283 if (copy_to_user(buf, text + skip, n)) {
1284 if (!len)
1285 len = -EFAULT;
1286 break;
1287 }
1288
1289 len += n;
1290 size -= n;
1291 buf += n;
1292 }
1293
1294 kfree(text);
1295 return len;
1296}
1297
1298static int syslog_print_all(char __user *buf, int size, bool clear)
1299{
1300 char *text;
1301 int len = 0;
1302
1303 text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
1304 if (!text)
1305 return -ENOMEM;
1306
1307 raw_spin_lock_irq(&logbuf_lock);
1308 if (buf) {
1309 u64 next_seq;
1310 u64 seq;
1311 u32 idx;
1312
1313 /*
1314 * Find first record that fits, including all following records,
1315 * into the user-provided buffer for this dump.
1316 */
1317 seq = clear_seq;
1318 idx = clear_idx;
1319 while (seq < log_next_seq) {
1320 struct printk_log *msg = log_from_idx(idx);
1321
1322 len += msg_print_text(msg, true, NULL, 0);
1323 idx = log_next(idx);
1324 seq++;
1325 }
1326
1327 /* move first record forward until length fits into the buffer */
1328 seq = clear_seq;
1329 idx = clear_idx;
1330 while (len > size && seq < log_next_seq) {
1331 struct printk_log *msg = log_from_idx(idx);
1332
1333 len -= msg_print_text(msg, true, NULL, 0);
1334 idx = log_next(idx);
1335 seq++;
1336 }
1337
1338 /* last message fitting into this dump */
1339 next_seq = log_next_seq;
1340
1341 len = 0;
1342 while (len >= 0 && seq < next_seq) {
1343 struct printk_log *msg = log_from_idx(idx);
1344 int textlen;
1345
1346 textlen = msg_print_text(msg, true, text,
1347 LOG_LINE_MAX + PREFIX_MAX);
1348 if (textlen < 0) {
1349 len = textlen;
1350 break;
1351 }
1352 idx = log_next(idx);
1353 seq++;
1354
1355 raw_spin_unlock_irq(&logbuf_lock);
1356 if (copy_to_user(buf + len, text, textlen))
1357 len = -EFAULT;
1358 else
1359 len += textlen;
1360 raw_spin_lock_irq(&logbuf_lock);
1361
1362 if (seq < log_first_seq) {
1363 /* messages are gone, move to next one */
1364 seq = log_first_seq;
1365 idx = log_first_idx;
1366 }
1367 }
1368 }
1369
1370 if (clear) {
1371 clear_seq = log_next_seq;
1372 clear_idx = log_next_idx;
1373 }
1374 raw_spin_unlock_irq(&logbuf_lock);
1375
1376 kfree(text);
1377 return len;
1378}
1379
1380int do_syslog(int type, char __user *buf, int len, int source)
1381{
1382 bool clear = false;
1383 static int saved_console_loglevel = LOGLEVEL_DEFAULT;
1384 int error;
1385
1386 error = check_syslog_permissions(type, source);
1387 if (error)
1388 goto out;
1389
1390 switch (type) {
1391 case SYSLOG_ACTION_CLOSE: /* Close log */
1392 break;
1393 case SYSLOG_ACTION_OPEN: /* Open log */
1394 break;
1395 case SYSLOG_ACTION_READ: /* Read from log */
1396 error = -EINVAL;
1397 if (!buf || len < 0)
1398 goto out;
1399 error = 0;
1400 if (!len)
1401 goto out;
1402 if (!access_ok(VERIFY_WRITE, buf, len)) {
1403 error = -EFAULT;
1404 goto out;
1405 }
1406 error = wait_event_interruptible(log_wait,
1407 syslog_seq != log_next_seq);
1408 if (error)
1409 goto out;
1410 error = syslog_print(buf, len);
1411 break;
1412 /* Read/clear last kernel messages */
1413 case SYSLOG_ACTION_READ_CLEAR:
1414 clear = true;
1415 /* FALL THRU */
1416 /* Read last kernel messages */
1417 case SYSLOG_ACTION_READ_ALL:
1418 error = -EINVAL;
1419 if (!buf || len < 0)
1420 goto out;
1421 error = 0;
1422 if (!len)
1423 goto out;
1424 if (!access_ok(VERIFY_WRITE, buf, len)) {
1425 error = -EFAULT;
1426 goto out;
1427 }
1428 error = syslog_print_all(buf, len, clear);
1429 break;
1430 /* Clear ring buffer */
1431 case SYSLOG_ACTION_CLEAR:
1432 syslog_print_all(NULL, 0, true);
1433 break;
1434 /* Disable logging to console */
1435 case SYSLOG_ACTION_CONSOLE_OFF:
1436 if (saved_console_loglevel == LOGLEVEL_DEFAULT)
1437 saved_console_loglevel = console_loglevel;
1438 console_loglevel = minimum_console_loglevel;
1439 break;
1440 /* Enable logging to console */
1441 case SYSLOG_ACTION_CONSOLE_ON:
1442 if (saved_console_loglevel != LOGLEVEL_DEFAULT) {
1443 console_loglevel = saved_console_loglevel;
1444 saved_console_loglevel = LOGLEVEL_DEFAULT;
1445 }
1446 break;
1447 /* Set level of messages printed to console */
1448 case SYSLOG_ACTION_CONSOLE_LEVEL:
1449 error = -EINVAL;
1450 if (len < 1 || len > 8)
1451 goto out;
1452 if (len < minimum_console_loglevel)
1453 len = minimum_console_loglevel;
1454 console_loglevel = len;
1455 /* Implicitly re-enable logging to console */
1456 saved_console_loglevel = LOGLEVEL_DEFAULT;
1457 error = 0;
1458 break;
1459 /* Number of chars in the log buffer */
1460 case SYSLOG_ACTION_SIZE_UNREAD:
1461 raw_spin_lock_irq(&logbuf_lock);
1462 if (syslog_seq < log_first_seq) {
1463 /* messages are gone, move to first one */
1464 syslog_seq = log_first_seq;
1465 syslog_idx = log_first_idx;
1466 syslog_partial = 0;
1467 }
1468 if (source == SYSLOG_FROM_PROC) {
1469 /*
1470 * Short-cut for poll(/"proc/kmsg") which simply checks
1471 * for pending data, not the size; return the count of
1472 * records, not the length.
1473 */
1474 error = log_next_seq - syslog_seq;
1475 } else {
1476 u64 seq = syslog_seq;
1477 u32 idx = syslog_idx;
1478
1479 error = 0;
1480 while (seq < log_next_seq) {
1481 struct printk_log *msg = log_from_idx(idx);
1482
1483 error += msg_print_text(msg, true, NULL, 0);
1484 idx = log_next(idx);
1485 seq++;
1486 }
1487 error -= syslog_partial;
1488 }
1489 raw_spin_unlock_irq(&logbuf_lock);
1490 break;
1491 /* Size of the log buffer */
1492 case SYSLOG_ACTION_SIZE_BUFFER:
1493 error = log_buf_len;
1494 break;
1495 default:
1496 error = -EINVAL;
1497 break;
1498 }
1499out:
1500 return error;
1501}
1502
1503SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
1504{
1505 return do_syslog(type, buf, len, SYSLOG_FROM_READER);
1506}
1507
1508/*
1509 * Call the console drivers, asking them to write out
1510 * log_buf[start] to log_buf[end - 1].
1511 * The console_lock must be held.
1512 */
1513static void call_console_drivers(int level,
1514 const char *ext_text, size_t ext_len,
1515 const char *text, size_t len)
1516{
1517 struct console *con;
1518
1519 trace_console_rcuidle(text, len);
1520
1521 if (!console_drivers)
1522 return;
1523
1524 for_each_console(con) {
1525 if (exclusive_console && con != exclusive_console)
1526 continue;
1527 if (!(con->flags & CON_ENABLED))
1528 continue;
1529 if (!con->write)
1530 continue;
1531 if (!cpu_online(smp_processor_id()) &&
1532 !(con->flags & CON_ANYTIME))
1533 continue;
1534 if (con->flags & CON_EXTENDED)
1535 con->write(con, ext_text, ext_len);
1536 else
1537 con->write(con, text, len);
1538 }
1539}
1540
1541/*
1542 * Zap console related locks when oopsing.
1543 * To leave time for slow consoles to print a full oops,
1544 * only zap at most once every 30 seconds.
1545 */
1546static void zap_locks(void)
1547{
1548 static unsigned long oops_timestamp;
1549
1550 if (time_after_eq(jiffies, oops_timestamp) &&
1551 !time_after(jiffies, oops_timestamp + 30 * HZ))
1552 return;
1553
1554 oops_timestamp = jiffies;
1555
1556 debug_locks_off();
1557 /* If a crash is occurring, make sure we can't deadlock */
1558 raw_spin_lock_init(&logbuf_lock);
1559 /* And make sure that we print immediately */
1560 sema_init(&console_sem, 1);
1561}
1562
1563int printk_delay_msec __read_mostly;
1564
1565static inline void printk_delay(void)
1566{
1567 if (unlikely(printk_delay_msec)) {
1568 int m = printk_delay_msec;
1569
1570 while (m--) {
1571 mdelay(1);
1572 touch_nmi_watchdog();
1573 }
1574 }
1575}
1576
1577/*
1578 * Continuation lines are buffered, and not committed to the record buffer
1579 * until the line is complete, or a race forces it. The line fragments
1580 * though, are printed immediately to the consoles to ensure everything has
1581 * reached the console in case of a kernel crash.
1582 */
1583static struct cont {
1584 char buf[LOG_LINE_MAX];
1585 size_t len; /* length == 0 means unused buffer */
1586 struct task_struct *owner; /* task of first print*/
1587 u64 ts_nsec; /* time of first print */
1588 u8 level; /* log level of first message */
1589 u8 facility; /* log facility of first message */
1590 enum log_flags flags; /* prefix, newline flags */
1591} cont;
1592
1593static void cont_flush(void)
1594{
1595 if (cont.len == 0)
1596 return;
1597
1598 log_store(cont.facility, cont.level, cont.flags, cont.ts_nsec,
1599 NULL, 0, cont.buf, cont.len);
1600 cont.len = 0;
1601}
1602
1603static bool cont_add(int facility, int level, enum log_flags flags, const char *text, size_t len)
1604{
1605 /*
1606 * If ext consoles are present, flush and skip in-kernel
1607 * continuation. See nr_ext_console_drivers definition. Also, if
1608 * the line gets too long, split it up in separate records.
1609 */
1610 if (nr_ext_console_drivers || cont.len + len > sizeof(cont.buf)) {
1611 cont_flush();
1612 return false;
1613 }
1614
1615 if (!cont.len) {
1616 cont.facility = facility;
1617 cont.level = level;
1618 cont.owner = current;
1619 cont.ts_nsec = local_clock();
1620 cont.flags = flags;
1621 }
1622
1623 memcpy(cont.buf + cont.len, text, len);
1624 cont.len += len;
1625
1626 // The original flags come from the first line,
1627 // but later continuations can add a newline.
1628 if (flags & LOG_NEWLINE) {
1629 cont.flags |= LOG_NEWLINE;
1630 cont_flush();
1631 }
1632
1633 if (cont.len > (sizeof(cont.buf) * 80) / 100)
1634 cont_flush();
1635
1636 return true;
1637}
1638
1639static size_t log_output(int facility, int level, enum log_flags lflags, const char *dict, size_t dictlen, char *text, size_t text_len)
1640{
1641 /*
1642 * If an earlier line was buffered, and we're a continuation
1643 * write from the same process, try to add it to the buffer.
1644 */
1645 if (cont.len) {
1646 if (cont.owner == current && (lflags & LOG_CONT)) {
1647 if (cont_add(facility, level, lflags, text, text_len))
1648 return text_len;
1649 }
1650 /* Otherwise, make sure it's flushed */
1651 cont_flush();
1652 }
1653
1654 /* Skip empty continuation lines that couldn't be added - they just flush */
1655 if (!text_len && (lflags & LOG_CONT))
1656 return 0;
1657
1658 /* If it doesn't end in a newline, try to buffer the current line */
1659 if (!(lflags & LOG_NEWLINE)) {
1660 if (cont_add(facility, level, lflags, text, text_len))
1661 return text_len;
1662 }
1663
1664 /* Store it in the record log */
1665 return log_store(facility, level, lflags, 0, dict, dictlen, text, text_len);
1666}
1667
1668asmlinkage int vprintk_emit(int facility, int level,
1669 const char *dict, size_t dictlen,
1670 const char *fmt, va_list args)
1671{
1672 static bool recursion_bug;
1673 static char textbuf[LOG_LINE_MAX];
1674 char *text = textbuf;
1675 size_t text_len = 0;
1676 enum log_flags lflags = 0;
1677 unsigned long flags;
1678 int this_cpu;
1679 int printed_len = 0;
1680 int nmi_message_lost;
1681 bool in_sched = false;
1682 /* cpu currently holding logbuf_lock in this function */
1683 static unsigned int logbuf_cpu = UINT_MAX;
1684
1685 if (level == LOGLEVEL_SCHED) {
1686 level = LOGLEVEL_DEFAULT;
1687 in_sched = true;
1688 }
1689
1690 boot_delay_msec(level);
1691 printk_delay();
1692
1693 local_irq_save(flags);
1694 this_cpu = smp_processor_id();
1695
1696 /*
1697 * Ouch, printk recursed into itself!
1698 */
1699 if (unlikely(logbuf_cpu == this_cpu)) {
1700 /*
1701 * If a crash is occurring during printk() on this CPU,
1702 * then try to get the crash message out but make sure
1703 * we can't deadlock. Otherwise just return to avoid the
1704 * recursion and return - but flag the recursion so that
1705 * it can be printed at the next appropriate moment:
1706 */
1707 if (!oops_in_progress && !lockdep_recursing(current)) {
1708 recursion_bug = true;
1709 local_irq_restore(flags);
1710 return 0;
1711 }
1712 zap_locks();
1713 }
1714
1715 lockdep_off();
1716 /* This stops the holder of console_sem just where we want him */
1717 raw_spin_lock(&logbuf_lock);
1718 logbuf_cpu = this_cpu;
1719
1720 if (unlikely(recursion_bug)) {
1721 static const char recursion_msg[] =
1722 "BUG: recent printk recursion!";
1723
1724 recursion_bug = false;
1725 /* emit KERN_CRIT message */
1726 printed_len += log_store(0, 2, LOG_PREFIX|LOG_NEWLINE, 0,
1727 NULL, 0, recursion_msg,
1728 strlen(recursion_msg));
1729 }
1730
1731 nmi_message_lost = get_nmi_message_lost();
1732 if (unlikely(nmi_message_lost)) {
1733 text_len = scnprintf(textbuf, sizeof(textbuf),
1734 "BAD LUCK: lost %d message(s) from NMI context!",
1735 nmi_message_lost);
1736 printed_len += log_store(0, 2, LOG_PREFIX|LOG_NEWLINE, 0,
1737 NULL, 0, textbuf, text_len);
1738 }
1739
1740 /*
1741 * The printf needs to come first; we need the syslog
1742 * prefix which might be passed-in as a parameter.
1743 */
1744 text_len = vscnprintf(text, sizeof(textbuf), fmt, args);
1745
1746 /* mark and strip a trailing newline */
1747 if (text_len && text[text_len-1] == '\n') {
1748 text_len--;
1749 lflags |= LOG_NEWLINE;
1750 }
1751
1752 /* strip kernel syslog prefix and extract log level or control flags */
1753 if (facility == 0) {
1754 int kern_level;
1755
1756 while ((kern_level = printk_get_level(text)) != 0) {
1757 switch (kern_level) {
1758 case '0' ... '7':
1759 if (level == LOGLEVEL_DEFAULT)
1760 level = kern_level - '0';
1761 /* fallthrough */
1762 case 'd': /* KERN_DEFAULT */
1763 lflags |= LOG_PREFIX;
1764 break;
1765 case 'c': /* KERN_CONT */
1766 lflags |= LOG_CONT;
1767 }
1768
1769 text_len -= 2;
1770 text += 2;
1771 }
1772 }
1773
1774 if (level == LOGLEVEL_DEFAULT)
1775 level = default_message_loglevel;
1776
1777 if (dict)
1778 lflags |= LOG_PREFIX|LOG_NEWLINE;
1779
1780 printed_len += log_output(facility, level, lflags, dict, dictlen, text, text_len);
1781
1782 logbuf_cpu = UINT_MAX;
1783 raw_spin_unlock(&logbuf_lock);
1784 lockdep_on();
1785 local_irq_restore(flags);
1786
1787 /* If called from the scheduler, we can not call up(). */
1788 if (!in_sched) {
1789 lockdep_off();
1790 /*
1791 * Try to acquire and then immediately release the console
1792 * semaphore. The release will print out buffers and wake up
1793 * /dev/kmsg and syslog() users.
1794 */
1795 if (console_trylock())
1796 console_unlock();
1797 lockdep_on();
1798 }
1799
1800 return printed_len;
1801}
1802EXPORT_SYMBOL(vprintk_emit);
1803
1804asmlinkage int vprintk(const char *fmt, va_list args)
1805{
1806 return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
1807}
1808EXPORT_SYMBOL(vprintk);
1809
1810asmlinkage int printk_emit(int facility, int level,
1811 const char *dict, size_t dictlen,
1812 const char *fmt, ...)
1813{
1814 va_list args;
1815 int r;
1816
1817 va_start(args, fmt);
1818 r = vprintk_emit(facility, level, dict, dictlen, fmt, args);
1819 va_end(args);
1820
1821 return r;
1822}
1823EXPORT_SYMBOL(printk_emit);
1824
1825int vprintk_default(const char *fmt, va_list args)
1826{
1827 int r;
1828
1829#ifdef CONFIG_KGDB_KDB
1830 /* Allow to pass printk() to kdb but avoid a recursion. */
1831 if (unlikely(kdb_trap_printk && kdb_printf_cpu < 0)) {
1832 r = vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
1833 return r;
1834 }
1835#endif
1836 r = vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
1837
1838 return r;
1839}
1840EXPORT_SYMBOL_GPL(vprintk_default);
1841
1842/**
1843 * printk - print a kernel message
1844 * @fmt: format string
1845 *
1846 * This is printk(). It can be called from any context. We want it to work.
1847 *
1848 * We try to grab the console_lock. If we succeed, it's easy - we log the
1849 * output and call the console drivers. If we fail to get the semaphore, we
1850 * place the output into the log buffer and return. The current holder of
1851 * the console_sem will notice the new output in console_unlock(); and will
1852 * send it to the consoles before releasing the lock.
1853 *
1854 * One effect of this deferred printing is that code which calls printk() and
1855 * then changes console_loglevel may break. This is because console_loglevel
1856 * is inspected when the actual printing occurs.
1857 *
1858 * See also:
1859 * printf(3)
1860 *
1861 * See the vsnprintf() documentation for format string extensions over C99.
1862 */
1863asmlinkage __visible int printk(const char *fmt, ...)
1864{
1865 va_list args;
1866 int r;
1867
1868 va_start(args, fmt);
1869 r = vprintk_func(fmt, args);
1870 va_end(args);
1871
1872 return r;
1873}
1874EXPORT_SYMBOL(printk);
1875
1876#else /* CONFIG_PRINTK */
1877
1878#define LOG_LINE_MAX 0
1879#define PREFIX_MAX 0
1880
1881static u64 syslog_seq;
1882static u32 syslog_idx;
1883static u64 console_seq;
1884static u32 console_idx;
1885static u64 log_first_seq;
1886static u32 log_first_idx;
1887static u64 log_next_seq;
1888static char *log_text(const struct printk_log *msg) { return NULL; }
1889static char *log_dict(const struct printk_log *msg) { return NULL; }
1890static struct printk_log *log_from_idx(u32 idx) { return NULL; }
1891static u32 log_next(u32 idx) { return 0; }
1892static ssize_t msg_print_ext_header(char *buf, size_t size,
1893 struct printk_log *msg,
1894 u64 seq) { return 0; }
1895static ssize_t msg_print_ext_body(char *buf, size_t size,
1896 char *dict, size_t dict_len,
1897 char *text, size_t text_len) { return 0; }
1898static void call_console_drivers(int level,
1899 const char *ext_text, size_t ext_len,
1900 const char *text, size_t len) {}
1901static size_t msg_print_text(const struct printk_log *msg,
1902 bool syslog, char *buf, size_t size) { return 0; }
1903static bool suppress_message_printing(int level) { return false; }
1904
1905/* Still needs to be defined for users */
1906DEFINE_PER_CPU(printk_func_t, printk_func);
1907
1908#endif /* CONFIG_PRINTK */
1909
1910#ifdef CONFIG_EARLY_PRINTK
1911struct console *early_console;
1912
1913asmlinkage __visible void early_printk(const char *fmt, ...)
1914{
1915 va_list ap;
1916 char buf[512];
1917 int n;
1918
1919 if (!early_console)
1920 return;
1921
1922 va_start(ap, fmt);
1923 n = vscnprintf(buf, sizeof(buf), fmt, ap);
1924 va_end(ap);
1925
1926 early_console->write(early_console, buf, n);
1927}
1928#endif
1929
1930static int __add_preferred_console(char *name, int idx, char *options,
1931 char *brl_options)
1932{
1933 struct console_cmdline *c;
1934 int i;
1935
1936 /*
1937 * See if this tty is not yet registered, and
1938 * if we have a slot free.
1939 */
1940 for (i = 0, c = console_cmdline;
1941 i < MAX_CMDLINECONSOLES && c->name[0];
1942 i++, c++) {
1943 if (strcmp(c->name, name) == 0 && c->index == idx) {
1944 if (!brl_options)
1945 selected_console = i;
1946 return 0;
1947 }
1948 }
1949 if (i == MAX_CMDLINECONSOLES)
1950 return -E2BIG;
1951 if (!brl_options)
1952 selected_console = i;
1953 strlcpy(c->name, name, sizeof(c->name));
1954 c->options = options;
1955 braille_set_options(c, brl_options);
1956
1957 c->index = idx;
1958 return 0;
1959}
1960/*
1961 * Set up a console. Called via do_early_param() in init/main.c
1962 * for each "console=" parameter in the boot command line.
1963 */
1964static int __init console_setup(char *str)
1965{
1966 char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for "ttyS" */
1967 char *s, *options, *brl_options = NULL;
1968 int idx;
1969
1970 if (_braille_console_setup(&str, &brl_options))
1971 return 1;
1972
1973 /*
1974 * Decode str into name, index, options.
1975 */
1976 if (str[0] >= '0' && str[0] <= '9') {
1977 strcpy(buf, "ttyS");
1978 strncpy(buf + 4, str, sizeof(buf) - 5);
1979 } else {
1980 strncpy(buf, str, sizeof(buf) - 1);
1981 }
1982 buf[sizeof(buf) - 1] = 0;
1983 options = strchr(str, ',');
1984 if (options)
1985 *(options++) = 0;
1986#ifdef __sparc__
1987 if (!strcmp(str, "ttya"))
1988 strcpy(buf, "ttyS0");
1989 if (!strcmp(str, "ttyb"))
1990 strcpy(buf, "ttyS1");
1991#endif
1992 for (s = buf; *s; s++)
1993 if (isdigit(*s) || *s == ',')
1994 break;
1995 idx = simple_strtoul(s, NULL, 10);
1996 *s = 0;
1997
1998 __add_preferred_console(buf, idx, options, brl_options);
1999 console_set_on_cmdline = 1;
2000 return 1;
2001}
2002__setup("console=", console_setup);
2003
2004/**
2005 * add_preferred_console - add a device to the list of preferred consoles.
2006 * @name: device name
2007 * @idx: device index
2008 * @options: options for this console
2009 *
2010 * The last preferred console added will be used for kernel messages
2011 * and stdin/out/err for init. Normally this is used by console_setup
2012 * above to handle user-supplied console arguments; however it can also
2013 * be used by arch-specific code either to override the user or more
2014 * commonly to provide a default console (ie from PROM variables) when
2015 * the user has not supplied one.
2016 */
2017int add_preferred_console(char *name, int idx, char *options)
2018{
2019 return __add_preferred_console(name, idx, options, NULL);
2020}
2021
2022bool console_suspend_enabled = true;
2023EXPORT_SYMBOL(console_suspend_enabled);
2024
2025static int __init console_suspend_disable(char *str)
2026{
2027 console_suspend_enabled = false;
2028 return 1;
2029}
2030__setup("no_console_suspend", console_suspend_disable);
2031module_param_named(console_suspend, console_suspend_enabled,
2032 bool, S_IRUGO | S_IWUSR);
2033MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
2034 " and hibernate operations");
2035
2036/**
2037 * suspend_console - suspend the console subsystem
2038 *
2039 * This disables printk() while we go into suspend states
2040 */
2041void suspend_console(void)
2042{
2043 if (!console_suspend_enabled)
2044 return;
2045 printk("Suspending console(s) (use no_console_suspend to debug)\n");
2046 console_lock();
2047 console_suspended = 1;
2048 up_console_sem();
2049}
2050
2051void resume_console(void)
2052{
2053 if (!console_suspend_enabled)
2054 return;
2055 down_console_sem();
2056 console_suspended = 0;
2057 console_unlock();
2058}
2059
2060/**
2061 * console_cpu_notify - print deferred console messages after CPU hotplug
2062 * @cpu: unused
2063 *
2064 * If printk() is called from a CPU that is not online yet, the messages
2065 * will be spooled but will not show up on the console. This function is
2066 * called when a new CPU comes online (or fails to come up), and ensures
2067 * that any such output gets printed.
2068 */
2069static int console_cpu_notify(unsigned int cpu)
2070{
2071 if (!cpuhp_tasks_frozen) {
2072 console_lock();
2073 console_unlock();
2074 }
2075 return 0;
2076}
2077
2078/**
2079 * console_lock - lock the console system for exclusive use.
2080 *
2081 * Acquires a lock which guarantees that the caller has
2082 * exclusive access to the console system and the console_drivers list.
2083 *
2084 * Can sleep, returns nothing.
2085 */
2086void console_lock(void)
2087{
2088 might_sleep();
2089
2090 down_console_sem();
2091 if (console_suspended)
2092 return;
2093 console_locked = 1;
2094 console_may_schedule = 1;
2095}
2096EXPORT_SYMBOL(console_lock);
2097
2098/**
2099 * console_trylock - try to lock the console system for exclusive use.
2100 *
2101 * Try to acquire a lock which guarantees that the caller has exclusive
2102 * access to the console system and the console_drivers list.
2103 *
2104 * returns 1 on success, and 0 on failure to acquire the lock.
2105 */
2106int console_trylock(void)
2107{
2108 if (down_trylock_console_sem())
2109 return 0;
2110 if (console_suspended) {
2111 up_console_sem();
2112 return 0;
2113 }
2114 console_locked = 1;
2115 /*
2116 * When PREEMPT_COUNT disabled we can't reliably detect if it's
2117 * safe to schedule (e.g. calling printk while holding a spin_lock),
2118 * because preempt_disable()/preempt_enable() are just barriers there
2119 * and preempt_count() is always 0.
2120 *
2121 * RCU read sections have a separate preemption counter when
2122 * PREEMPT_RCU enabled thus we must take extra care and check
2123 * rcu_preempt_depth(), otherwise RCU read sections modify
2124 * preempt_count().
2125 */
2126 console_may_schedule = !oops_in_progress &&
2127 preemptible() &&
2128 !rcu_preempt_depth();
2129 return 1;
2130}
2131EXPORT_SYMBOL(console_trylock);
2132
2133int is_console_locked(void)
2134{
2135 return console_locked;
2136}
2137
2138/*
2139 * Check if we have any console that is capable of printing while cpu is
2140 * booting or shutting down. Requires console_sem.
2141 */
2142static int have_callable_console(void)
2143{
2144 struct console *con;
2145
2146 for_each_console(con)
2147 if ((con->flags & CON_ENABLED) &&
2148 (con->flags & CON_ANYTIME))
2149 return 1;
2150
2151 return 0;
2152}
2153
2154/*
2155 * Can we actually use the console at this time on this cpu?
2156 *
2157 * Console drivers may assume that per-cpu resources have been allocated. So
2158 * unless they're explicitly marked as being able to cope (CON_ANYTIME) don't
2159 * call them until this CPU is officially up.
2160 */
2161static inline int can_use_console(void)
2162{
2163 return cpu_online(raw_smp_processor_id()) || have_callable_console();
2164}
2165
2166/**
2167 * console_unlock - unlock the console system
2168 *
2169 * Releases the console_lock which the caller holds on the console system
2170 * and the console driver list.
2171 *
2172 * While the console_lock was held, console output may have been buffered
2173 * by printk(). If this is the case, console_unlock(); emits
2174 * the output prior to releasing the lock.
2175 *
2176 * If there is output waiting, we wake /dev/kmsg and syslog() users.
2177 *
2178 * console_unlock(); may be called from any context.
2179 */
2180void console_unlock(void)
2181{
2182 static char ext_text[CONSOLE_EXT_LOG_MAX];
2183 static char text[LOG_LINE_MAX + PREFIX_MAX];
2184 static u64 seen_seq;
2185 unsigned long flags;
2186 bool wake_klogd = false;
2187 bool do_cond_resched, retry;
2188
2189 if (console_suspended) {
2190 up_console_sem();
2191 return;
2192 }
2193
2194 /*
2195 * Console drivers are called under logbuf_lock, so
2196 * @console_may_schedule should be cleared before; however, we may
2197 * end up dumping a lot of lines, for example, if called from
2198 * console registration path, and should invoke cond_resched()
2199 * between lines if allowable. Not doing so can cause a very long
2200 * scheduling stall on a slow console leading to RCU stall and
2201 * softlockup warnings which exacerbate the issue with more
2202 * messages practically incapacitating the system.
2203 */
2204 do_cond_resched = console_may_schedule;
2205 console_may_schedule = 0;
2206
2207again:
2208 /*
2209 * We released the console_sem lock, so we need to recheck if
2210 * cpu is online and (if not) is there at least one CON_ANYTIME
2211 * console.
2212 */
2213 if (!can_use_console()) {
2214 console_locked = 0;
2215 up_console_sem();
2216 return;
2217 }
2218
2219 for (;;) {
2220 struct printk_log *msg;
2221 size_t ext_len = 0;
2222 size_t len;
2223 int level;
2224
2225 raw_spin_lock_irqsave(&logbuf_lock, flags);
2226 if (seen_seq != log_next_seq) {
2227 wake_klogd = true;
2228 seen_seq = log_next_seq;
2229 }
2230
2231 if (console_seq < log_first_seq) {
2232 len = sprintf(text, "** %u printk messages dropped ** ",
2233 (unsigned)(log_first_seq - console_seq));
2234
2235 /* messages are gone, move to first one */
2236 console_seq = log_first_seq;
2237 console_idx = log_first_idx;
2238 } else {
2239 len = 0;
2240 }
2241skip:
2242 if (console_seq == log_next_seq)
2243 break;
2244
2245 msg = log_from_idx(console_idx);
2246 level = msg->level;
2247 if (suppress_message_printing(level)) {
2248 /*
2249 * Skip record we have buffered and already printed
2250 * directly to the console when we received it, and
2251 * record that has level above the console loglevel.
2252 */
2253 console_idx = log_next(console_idx);
2254 console_seq++;
2255 goto skip;
2256 }
2257
2258 len += msg_print_text(msg, false, text + len, sizeof(text) - len);
2259 if (nr_ext_console_drivers) {
2260 ext_len = msg_print_ext_header(ext_text,
2261 sizeof(ext_text),
2262 msg, console_seq);
2263 ext_len += msg_print_ext_body(ext_text + ext_len,
2264 sizeof(ext_text) - ext_len,
2265 log_dict(msg), msg->dict_len,
2266 log_text(msg), msg->text_len);
2267 }
2268 console_idx = log_next(console_idx);
2269 console_seq++;
2270 raw_spin_unlock(&logbuf_lock);
2271
2272 stop_critical_timings(); /* don't trace print latency */
2273 call_console_drivers(level, ext_text, ext_len, text, len);
2274 start_critical_timings();
2275 local_irq_restore(flags);
2276
2277 if (do_cond_resched)
2278 cond_resched();
2279 }
2280 console_locked = 0;
2281
2282 /* Release the exclusive_console once it is used */
2283 if (unlikely(exclusive_console))
2284 exclusive_console = NULL;
2285
2286 raw_spin_unlock(&logbuf_lock);
2287
2288 up_console_sem();
2289
2290 /*
2291 * Someone could have filled up the buffer again, so re-check if there's
2292 * something to flush. In case we cannot trylock the console_sem again,
2293 * there's a new owner and the console_unlock() from them will do the
2294 * flush, no worries.
2295 */
2296 raw_spin_lock(&logbuf_lock);
2297 retry = console_seq != log_next_seq;
2298 raw_spin_unlock_irqrestore(&logbuf_lock, flags);
2299
2300 if (retry && console_trylock())
2301 goto again;
2302
2303 if (wake_klogd)
2304 wake_up_klogd();
2305}
2306EXPORT_SYMBOL(console_unlock);
2307
2308/**
2309 * console_conditional_schedule - yield the CPU if required
2310 *
2311 * If the console code is currently allowed to sleep, and
2312 * if this CPU should yield the CPU to another task, do
2313 * so here.
2314 *
2315 * Must be called within console_lock();.
2316 */
2317void __sched console_conditional_schedule(void)
2318{
2319 if (console_may_schedule)
2320 cond_resched();
2321}
2322EXPORT_SYMBOL(console_conditional_schedule);
2323
2324void console_unblank(void)
2325{
2326 struct console *c;
2327
2328 /*
2329 * console_unblank can no longer be called in interrupt context unless
2330 * oops_in_progress is set to 1..
2331 */
2332 if (oops_in_progress) {
2333 if (down_trylock_console_sem() != 0)
2334 return;
2335 } else
2336 console_lock();
2337
2338 console_locked = 1;
2339 console_may_schedule = 0;
2340 for_each_console(c)
2341 if ((c->flags & CON_ENABLED) && c->unblank)
2342 c->unblank();
2343 console_unlock();
2344}
2345
2346/**
2347 * console_flush_on_panic - flush console content on panic
2348 *
2349 * Immediately output all pending messages no matter what.
2350 */
2351void console_flush_on_panic(void)
2352{
2353 /*
2354 * If someone else is holding the console lock, trylock will fail
2355 * and may_schedule may be set. Ignore and proceed to unlock so
2356 * that messages are flushed out. As this can be called from any
2357 * context and we don't want to get preempted while flushing,
2358 * ensure may_schedule is cleared.
2359 */
2360 console_trylock();
2361 console_may_schedule = 0;
2362 console_unlock();
2363}
2364
2365/*
2366 * Return the console tty driver structure and its associated index
2367 */
2368struct tty_driver *console_device(int *index)
2369{
2370 struct console *c;
2371 struct tty_driver *driver = NULL;
2372
2373 console_lock();
2374 for_each_console(c) {
2375 if (!c->device)
2376 continue;
2377 driver = c->device(c, index);
2378 if (driver)
2379 break;
2380 }
2381 console_unlock();
2382 return driver;
2383}
2384
2385/*
2386 * Prevent further output on the passed console device so that (for example)
2387 * serial drivers can disable console output before suspending a port, and can
2388 * re-enable output afterwards.
2389 */
2390void console_stop(struct console *console)
2391{
2392 console_lock();
2393 console->flags &= ~CON_ENABLED;
2394 console_unlock();
2395}
2396EXPORT_SYMBOL(console_stop);
2397
2398void console_start(struct console *console)
2399{
2400 console_lock();
2401 console->flags |= CON_ENABLED;
2402 console_unlock();
2403}
2404EXPORT_SYMBOL(console_start);
2405
2406static int __read_mostly keep_bootcon;
2407
2408static int __init keep_bootcon_setup(char *str)
2409{
2410 keep_bootcon = 1;
2411 pr_info("debug: skip boot console de-registration.\n");
2412
2413 return 0;
2414}
2415
2416early_param("keep_bootcon", keep_bootcon_setup);
2417
2418/*
2419 * The console driver calls this routine during kernel initialization
2420 * to register the console printing procedure with printk() and to
2421 * print any messages that were printed by the kernel before the
2422 * console driver was initialized.
2423 *
2424 * This can happen pretty early during the boot process (because of
2425 * early_printk) - sometimes before setup_arch() completes - be careful
2426 * of what kernel features are used - they may not be initialised yet.
2427 *
2428 * There are two types of consoles - bootconsoles (early_printk) and
2429 * "real" consoles (everything which is not a bootconsole) which are
2430 * handled differently.
2431 * - Any number of bootconsoles can be registered at any time.
2432 * - As soon as a "real" console is registered, all bootconsoles
2433 * will be unregistered automatically.
2434 * - Once a "real" console is registered, any attempt to register a
2435 * bootconsoles will be rejected
2436 */
2437void register_console(struct console *newcon)
2438{
2439 int i;
2440 unsigned long flags;
2441 struct console *bcon = NULL;
2442 struct console_cmdline *c;
2443
2444 if (console_drivers)
2445 for_each_console(bcon)
2446 if (WARN(bcon == newcon,
2447 "console '%s%d' already registered\n",
2448 bcon->name, bcon->index))
2449 return;
2450
2451 /*
2452 * before we register a new CON_BOOT console, make sure we don't
2453 * already have a valid console
2454 */
2455 if (console_drivers && newcon->flags & CON_BOOT) {
2456 /* find the last or real console */
2457 for_each_console(bcon) {
2458 if (!(bcon->flags & CON_BOOT)) {
2459 pr_info("Too late to register bootconsole %s%d\n",
2460 newcon->name, newcon->index);
2461 return;
2462 }
2463 }
2464 }
2465
2466 if (console_drivers && console_drivers->flags & CON_BOOT)
2467 bcon = console_drivers;
2468
2469 if (preferred_console < 0 || bcon || !console_drivers)
2470 preferred_console = selected_console;
2471
2472 /*
2473 * See if we want to use this console driver. If we
2474 * didn't select a console we take the first one
2475 * that registers here.
2476 */
2477 if (preferred_console < 0) {
2478 if (newcon->index < 0)
2479 newcon->index = 0;
2480 if (newcon->setup == NULL ||
2481 newcon->setup(newcon, NULL) == 0) {
2482 newcon->flags |= CON_ENABLED;
2483 if (newcon->device) {
2484 newcon->flags |= CON_CONSDEV;
2485 preferred_console = 0;
2486 }
2487 }
2488 }
2489
2490 /*
2491 * See if this console matches one we selected on
2492 * the command line.
2493 */
2494 for (i = 0, c = console_cmdline;
2495 i < MAX_CMDLINECONSOLES && c->name[0];
2496 i++, c++) {
2497 if (!newcon->match ||
2498 newcon->match(newcon, c->name, c->index, c->options) != 0) {
2499 /* default matching */
2500 BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));
2501 if (strcmp(c->name, newcon->name) != 0)
2502 continue;
2503 if (newcon->index >= 0 &&
2504 newcon->index != c->index)
2505 continue;
2506 if (newcon->index < 0)
2507 newcon->index = c->index;
2508
2509 if (_braille_register_console(newcon, c))
2510 return;
2511
2512 if (newcon->setup &&
2513 newcon->setup(newcon, c->options) != 0)
2514 break;
2515 }
2516
2517 newcon->flags |= CON_ENABLED;
2518 if (i == selected_console) {
2519 newcon->flags |= CON_CONSDEV;
2520 preferred_console = selected_console;
2521 }
2522 break;
2523 }
2524
2525 if (!(newcon->flags & CON_ENABLED))
2526 return;
2527
2528 /*
2529 * If we have a bootconsole, and are switching to a real console,
2530 * don't print everything out again, since when the boot console, and
2531 * the real console are the same physical device, it's annoying to
2532 * see the beginning boot messages twice
2533 */
2534 if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
2535 newcon->flags &= ~CON_PRINTBUFFER;
2536
2537 /*
2538 * Put this console in the list - keep the
2539 * preferred driver at the head of the list.
2540 */
2541 console_lock();
2542 if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
2543 newcon->next = console_drivers;
2544 console_drivers = newcon;
2545 if (newcon->next)
2546 newcon->next->flags &= ~CON_CONSDEV;
2547 } else {
2548 newcon->next = console_drivers->next;
2549 console_drivers->next = newcon;
2550 }
2551
2552 if (newcon->flags & CON_EXTENDED)
2553 if (!nr_ext_console_drivers++)
2554 pr_info("printk: continuation disabled due to ext consoles, expect more fragments in /dev/kmsg\n");
2555
2556 if (newcon->flags & CON_PRINTBUFFER) {
2557 /*
2558 * console_unlock(); will print out the buffered messages
2559 * for us.
2560 */
2561 raw_spin_lock_irqsave(&logbuf_lock, flags);
2562 console_seq = syslog_seq;
2563 console_idx = syslog_idx;
2564 raw_spin_unlock_irqrestore(&logbuf_lock, flags);
2565 /*
2566 * We're about to replay the log buffer. Only do this to the
2567 * just-registered console to avoid excessive message spam to
2568 * the already-registered consoles.
2569 */
2570 exclusive_console = newcon;
2571 }
2572 console_unlock();
2573 console_sysfs_notify();
2574
2575 /*
2576 * By unregistering the bootconsoles after we enable the real console
2577 * we get the "console xxx enabled" message on all the consoles -
2578 * boot consoles, real consoles, etc - this is to ensure that end
2579 * users know there might be something in the kernel's log buffer that
2580 * went to the bootconsole (that they do not see on the real console)
2581 */
2582 pr_info("%sconsole [%s%d] enabled\n",
2583 (newcon->flags & CON_BOOT) ? "boot" : "" ,
2584 newcon->name, newcon->index);
2585 if (bcon &&
2586 ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) &&
2587 !keep_bootcon) {
2588 /* We need to iterate through all boot consoles, to make
2589 * sure we print everything out, before we unregister them.
2590 */
2591 for_each_console(bcon)
2592 if (bcon->flags & CON_BOOT)
2593 unregister_console(bcon);
2594 }
2595}
2596EXPORT_SYMBOL(register_console);
2597
2598int unregister_console(struct console *console)
2599{
2600 struct console *a, *b;
2601 int res;
2602
2603 pr_info("%sconsole [%s%d] disabled\n",
2604 (console->flags & CON_BOOT) ? "boot" : "" ,
2605 console->name, console->index);
2606
2607 res = _braille_unregister_console(console);
2608 if (res)
2609 return res;
2610
2611 res = 1;
2612 console_lock();
2613 if (console_drivers == console) {
2614 console_drivers=console->next;
2615 res = 0;
2616 } else if (console_drivers) {
2617 for (a=console_drivers->next, b=console_drivers ;
2618 a; b=a, a=b->next) {
2619 if (a == console) {
2620 b->next = a->next;
2621 res = 0;
2622 break;
2623 }
2624 }
2625 }
2626
2627 if (!res && (console->flags & CON_EXTENDED))
2628 nr_ext_console_drivers--;
2629
2630 /*
2631 * If this isn't the last console and it has CON_CONSDEV set, we
2632 * need to set it on the next preferred console.
2633 */
2634 if (console_drivers != NULL && console->flags & CON_CONSDEV)
2635 console_drivers->flags |= CON_CONSDEV;
2636
2637 console->flags &= ~CON_ENABLED;
2638 console_unlock();
2639 console_sysfs_notify();
2640 return res;
2641}
2642EXPORT_SYMBOL(unregister_console);
2643
2644/*
2645 * Some boot consoles access data that is in the init section and which will
2646 * be discarded after the initcalls have been run. To make sure that no code
2647 * will access this data, unregister the boot consoles in a late initcall.
2648 *
2649 * If for some reason, such as deferred probe or the driver being a loadable
2650 * module, the real console hasn't registered yet at this point, there will
2651 * be a brief interval in which no messages are logged to the console, which
2652 * makes it difficult to diagnose problems that occur during this time.
2653 *
2654 * To mitigate this problem somewhat, only unregister consoles whose memory
2655 * intersects with the init section. Note that code exists elsewhere to get
2656 * rid of the boot console as soon as the proper console shows up, so there
2657 * won't be side-effects from postponing the removal.
2658 */
2659static int __init printk_late_init(void)
2660{
2661 struct console *con;
2662 int ret;
2663
2664 for_each_console(con) {
2665 if (!keep_bootcon && con->flags & CON_BOOT) {
2666 /*
2667 * Make sure to unregister boot consoles whose data
2668 * resides in the init section before the init section
2669 * is discarded. Boot consoles whose data will stick
2670 * around will automatically be unregistered when the
2671 * proper console replaces them.
2672 */
2673 if (init_section_intersects(con, sizeof(*con)))
2674 unregister_console(con);
2675 }
2676 }
2677 ret = cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD, "printk:dead", NULL,
2678 console_cpu_notify);
2679 WARN_ON(ret < 0);
2680 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "printk:online",
2681 console_cpu_notify, NULL);
2682 WARN_ON(ret < 0);
2683 return 0;
2684}
2685late_initcall(printk_late_init);
2686
2687#if defined CONFIG_PRINTK
2688/*
2689 * Delayed printk version, for scheduler-internal messages:
2690 */
2691#define PRINTK_PENDING_WAKEUP 0x01
2692#define PRINTK_PENDING_OUTPUT 0x02
2693
2694static DEFINE_PER_CPU(int, printk_pending);
2695
2696static void wake_up_klogd_work_func(struct irq_work *irq_work)
2697{
2698 int pending = __this_cpu_xchg(printk_pending, 0);
2699
2700 if (pending & PRINTK_PENDING_OUTPUT) {
2701 /* If trylock fails, someone else is doing the printing */
2702 if (console_trylock())
2703 console_unlock();
2704 }
2705
2706 if (pending & PRINTK_PENDING_WAKEUP)
2707 wake_up_interruptible(&log_wait);
2708}
2709
2710static DEFINE_PER_CPU(struct irq_work, wake_up_klogd_work) = {
2711 .func = wake_up_klogd_work_func,
2712 .flags = IRQ_WORK_LAZY,
2713};
2714
2715void wake_up_klogd(void)
2716{
2717 preempt_disable();
2718 if (waitqueue_active(&log_wait)) {
2719 this_cpu_or(printk_pending, PRINTK_PENDING_WAKEUP);
2720 irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
2721 }
2722 preempt_enable();
2723}
2724
2725int printk_deferred(const char *fmt, ...)
2726{
2727 va_list args;
2728 int r;
2729
2730 preempt_disable();
2731 va_start(args, fmt);
2732 r = vprintk_emit(0, LOGLEVEL_SCHED, NULL, 0, fmt, args);
2733 va_end(args);
2734
2735 __this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
2736 irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
2737 preempt_enable();
2738
2739 return r;
2740}
2741
2742/*
2743 * printk rate limiting, lifted from the networking subsystem.
2744 *
2745 * This enforces a rate limit: not more than 10 kernel messages
2746 * every 5s to make a denial-of-service attack impossible.
2747 */
2748DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
2749
2750int __printk_ratelimit(const char *func)
2751{
2752 return ___ratelimit(&printk_ratelimit_state, func);
2753}
2754EXPORT_SYMBOL(__printk_ratelimit);
2755
2756/**
2757 * printk_timed_ratelimit - caller-controlled printk ratelimiting
2758 * @caller_jiffies: pointer to caller's state
2759 * @interval_msecs: minimum interval between prints
2760 *
2761 * printk_timed_ratelimit() returns true if more than @interval_msecs
2762 * milliseconds have elapsed since the last time printk_timed_ratelimit()
2763 * returned true.
2764 */
2765bool printk_timed_ratelimit(unsigned long *caller_jiffies,
2766 unsigned int interval_msecs)
2767{
2768 unsigned long elapsed = jiffies - *caller_jiffies;
2769
2770 if (*caller_jiffies && elapsed <= msecs_to_jiffies(interval_msecs))
2771 return false;
2772
2773 *caller_jiffies = jiffies;
2774 return true;
2775}
2776EXPORT_SYMBOL(printk_timed_ratelimit);
2777
2778static DEFINE_SPINLOCK(dump_list_lock);
2779static LIST_HEAD(dump_list);
2780
2781/**
2782 * kmsg_dump_register - register a kernel log dumper.
2783 * @dumper: pointer to the kmsg_dumper structure
2784 *
2785 * Adds a kernel log dumper to the system. The dump callback in the
2786 * structure will be called when the kernel oopses or panics and must be
2787 * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
2788 */
2789int kmsg_dump_register(struct kmsg_dumper *dumper)
2790{
2791 unsigned long flags;
2792 int err = -EBUSY;
2793
2794 /* The dump callback needs to be set */
2795 if (!dumper->dump)
2796 return -EINVAL;
2797
2798 spin_lock_irqsave(&dump_list_lock, flags);
2799 /* Don't allow registering multiple times */
2800 if (!dumper->registered) {
2801 dumper->registered = 1;
2802 list_add_tail_rcu(&dumper->list, &dump_list);
2803 err = 0;
2804 }
2805 spin_unlock_irqrestore(&dump_list_lock, flags);
2806
2807 return err;
2808}
2809EXPORT_SYMBOL_GPL(kmsg_dump_register);
2810
2811/**
2812 * kmsg_dump_unregister - unregister a kmsg dumper.
2813 * @dumper: pointer to the kmsg_dumper structure
2814 *
2815 * Removes a dump device from the system. Returns zero on success and
2816 * %-EINVAL otherwise.
2817 */
2818int kmsg_dump_unregister(struct kmsg_dumper *dumper)
2819{
2820 unsigned long flags;
2821 int err = -EINVAL;
2822
2823 spin_lock_irqsave(&dump_list_lock, flags);
2824 if (dumper->registered) {
2825 dumper->registered = 0;
2826 list_del_rcu(&dumper->list);
2827 err = 0;
2828 }
2829 spin_unlock_irqrestore(&dump_list_lock, flags);
2830 synchronize_rcu();
2831
2832 return err;
2833}
2834EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
2835
2836static bool always_kmsg_dump;
2837module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);
2838
2839/**
2840 * kmsg_dump - dump kernel log to kernel message dumpers.
2841 * @reason: the reason (oops, panic etc) for dumping
2842 *
2843 * Call each of the registered dumper's dump() callback, which can
2844 * retrieve the kmsg records with kmsg_dump_get_line() or
2845 * kmsg_dump_get_buffer().
2846 */
2847void kmsg_dump(enum kmsg_dump_reason reason)
2848{
2849 struct kmsg_dumper *dumper;
2850 unsigned long flags;
2851
2852 if ((reason > KMSG_DUMP_OOPS) && !always_kmsg_dump)
2853 return;
2854
2855 rcu_read_lock();
2856 list_for_each_entry_rcu(dumper, &dump_list, list) {
2857 if (dumper->max_reason && reason > dumper->max_reason)
2858 continue;
2859
2860 /* initialize iterator with data about the stored records */
2861 dumper->active = true;
2862
2863 raw_spin_lock_irqsave(&logbuf_lock, flags);
2864 dumper->cur_seq = clear_seq;
2865 dumper->cur_idx = clear_idx;
2866 dumper->next_seq = log_next_seq;
2867 dumper->next_idx = log_next_idx;
2868 raw_spin_unlock_irqrestore(&logbuf_lock, flags);
2869
2870 /* invoke dumper which will iterate over records */
2871 dumper->dump(dumper, reason);
2872
2873 /* reset iterator */
2874 dumper->active = false;
2875 }
2876 rcu_read_unlock();
2877}
2878
2879/**
2880 * kmsg_dump_get_line_nolock - retrieve one kmsg log line (unlocked version)
2881 * @dumper: registered kmsg dumper
2882 * @syslog: include the "<4>" prefixes
2883 * @line: buffer to copy the line to
2884 * @size: maximum size of the buffer
2885 * @len: length of line placed into buffer
2886 *
2887 * Start at the beginning of the kmsg buffer, with the oldest kmsg
2888 * record, and copy one record into the provided buffer.
2889 *
2890 * Consecutive calls will return the next available record moving
2891 * towards the end of the buffer with the youngest messages.
2892 *
2893 * A return value of FALSE indicates that there are no more records to
2894 * read.
2895 *
2896 * The function is similar to kmsg_dump_get_line(), but grabs no locks.
2897 */
2898bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
2899 char *line, size_t size, size_t *len)
2900{
2901 struct printk_log *msg;
2902 size_t l = 0;
2903 bool ret = false;
2904
2905 if (!dumper->active)
2906 goto out;
2907
2908 if (dumper->cur_seq < log_first_seq) {
2909 /* messages are gone, move to first available one */
2910 dumper->cur_seq = log_first_seq;
2911 dumper->cur_idx = log_first_idx;
2912 }
2913
2914 /* last entry */
2915 if (dumper->cur_seq >= log_next_seq)
2916 goto out;
2917
2918 msg = log_from_idx(dumper->cur_idx);
2919 l = msg_print_text(msg, syslog, line, size);
2920
2921 dumper->cur_idx = log_next(dumper->cur_idx);
2922 dumper->cur_seq++;
2923 ret = true;
2924out:
2925 if (len)
2926 *len = l;
2927 return ret;
2928}
2929
2930/**
2931 * kmsg_dump_get_line - retrieve one kmsg log line
2932 * @dumper: registered kmsg dumper
2933 * @syslog: include the "<4>" prefixes
2934 * @line: buffer to copy the line to
2935 * @size: maximum size of the buffer
2936 * @len: length of line placed into buffer
2937 *
2938 * Start at the beginning of the kmsg buffer, with the oldest kmsg
2939 * record, and copy one record into the provided buffer.
2940 *
2941 * Consecutive calls will return the next available record moving
2942 * towards the end of the buffer with the youngest messages.
2943 *
2944 * A return value of FALSE indicates that there are no more records to
2945 * read.
2946 */
2947bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
2948 char *line, size_t size, size_t *len)
2949{
2950 unsigned long flags;
2951 bool ret;
2952
2953 raw_spin_lock_irqsave(&logbuf_lock, flags);
2954 ret = kmsg_dump_get_line_nolock(dumper, syslog, line, size, len);
2955 raw_spin_unlock_irqrestore(&logbuf_lock, flags);
2956
2957 return ret;
2958}
2959EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
2960
2961/**
2962 * kmsg_dump_get_buffer - copy kmsg log lines
2963 * @dumper: registered kmsg dumper
2964 * @syslog: include the "<4>" prefixes
2965 * @buf: buffer to copy the line to
2966 * @size: maximum size of the buffer
2967 * @len: length of line placed into buffer
2968 *
2969 * Start at the end of the kmsg buffer and fill the provided buffer
2970 * with as many of the the *youngest* kmsg records that fit into it.
2971 * If the buffer is large enough, all available kmsg records will be
2972 * copied with a single call.
2973 *
2974 * Consecutive calls will fill the buffer with the next block of
2975 * available older records, not including the earlier retrieved ones.
2976 *
2977 * A return value of FALSE indicates that there are no more records to
2978 * read.
2979 */
2980bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
2981 char *buf, size_t size, size_t *len)
2982{
2983 unsigned long flags;
2984 u64 seq;
2985 u32 idx;
2986 u64 next_seq;
2987 u32 next_idx;
2988 size_t l = 0;
2989 bool ret = false;
2990
2991 if (!dumper->active)
2992 goto out;
2993
2994 raw_spin_lock_irqsave(&logbuf_lock, flags);
2995 if (dumper->cur_seq < log_first_seq) {
2996 /* messages are gone, move to first available one */
2997 dumper->cur_seq = log_first_seq;
2998 dumper->cur_idx = log_first_idx;
2999 }
3000
3001 /* last entry */
3002 if (dumper->cur_seq >= dumper->next_seq) {
3003 raw_spin_unlock_irqrestore(&logbuf_lock, flags);
3004 goto out;
3005 }
3006
3007 /* calculate length of entire buffer */
3008 seq = dumper->cur_seq;
3009 idx = dumper->cur_idx;
3010 while (seq < dumper->next_seq) {
3011 struct printk_log *msg = log_from_idx(idx);
3012
3013 l += msg_print_text(msg, true, NULL, 0);
3014 idx = log_next(idx);
3015 seq++;
3016 }
3017
3018 /* move first record forward until length fits into the buffer */
3019 seq = dumper->cur_seq;
3020 idx = dumper->cur_idx;
3021 while (l > size && seq < dumper->next_seq) {
3022 struct printk_log *msg = log_from_idx(idx);
3023
3024 l -= msg_print_text(msg, true, NULL, 0);
3025 idx = log_next(idx);
3026 seq++;
3027 }
3028
3029 /* last message in next interation */
3030 next_seq = seq;
3031 next_idx = idx;
3032
3033 l = 0;
3034 while (seq < dumper->next_seq) {
3035 struct printk_log *msg = log_from_idx(idx);
3036
3037 l += msg_print_text(msg, syslog, buf + l, size - l);
3038 idx = log_next(idx);
3039 seq++;
3040 }
3041
3042 dumper->next_seq = next_seq;
3043 dumper->next_idx = next_idx;
3044 ret = true;
3045 raw_spin_unlock_irqrestore(&logbuf_lock, flags);
3046out:
3047 if (len)
3048 *len = l;
3049 return ret;
3050}
3051EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
3052
3053/**
3054 * kmsg_dump_rewind_nolock - reset the interator (unlocked version)
3055 * @dumper: registered kmsg dumper
3056 *
3057 * Reset the dumper's iterator so that kmsg_dump_get_line() and
3058 * kmsg_dump_get_buffer() can be called again and used multiple
3059 * times within the same dumper.dump() callback.
3060 *
3061 * The function is similar to kmsg_dump_rewind(), but grabs no locks.
3062 */
3063void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
3064{
3065 dumper->cur_seq = clear_seq;
3066 dumper->cur_idx = clear_idx;
3067 dumper->next_seq = log_next_seq;
3068 dumper->next_idx = log_next_idx;
3069}
3070
3071/**
3072 * kmsg_dump_rewind - reset the interator
3073 * @dumper: registered kmsg dumper
3074 *
3075 * Reset the dumper's iterator so that kmsg_dump_get_line() and
3076 * kmsg_dump_get_buffer() can be called again and used multiple
3077 * times within the same dumper.dump() callback.
3078 */
3079void kmsg_dump_rewind(struct kmsg_dumper *dumper)
3080{
3081 unsigned long flags;
3082
3083 raw_spin_lock_irqsave(&logbuf_lock, flags);
3084 kmsg_dump_rewind_nolock(dumper);
3085 raw_spin_unlock_irqrestore(&logbuf_lock, flags);
3086}
3087EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
3088
3089static char dump_stack_arch_desc_str[128];
3090
3091/**
3092 * dump_stack_set_arch_desc - set arch-specific str to show with task dumps
3093 * @fmt: printf-style format string
3094 * @...: arguments for the format string
3095 *
3096 * The configured string will be printed right after utsname during task
3097 * dumps. Usually used to add arch-specific system identifiers. If an
3098 * arch wants to make use of such an ID string, it should initialize this
3099 * as soon as possible during boot.
3100 */
3101void __init dump_stack_set_arch_desc(const char *fmt, ...)
3102{
3103 va_list args;
3104
3105 va_start(args, fmt);
3106 vsnprintf(dump_stack_arch_desc_str, sizeof(dump_stack_arch_desc_str),
3107 fmt, args);
3108 va_end(args);
3109}
3110
3111/**
3112 * dump_stack_print_info - print generic debug info for dump_stack()
3113 * @log_lvl: log level
3114 *
3115 * Arch-specific dump_stack() implementations can use this function to
3116 * print out the same debug information as the generic dump_stack().
3117 */
3118void dump_stack_print_info(const char *log_lvl)
3119{
3120 printk("%sCPU: %d PID: %d Comm: %.20s %s %s %.*s\n",
3121 log_lvl, raw_smp_processor_id(), current->pid, current->comm,
3122 print_tainted(), init_utsname()->release,
3123 (int)strcspn(init_utsname()->version, " "),
3124 init_utsname()->version);
3125
3126 if (dump_stack_arch_desc_str[0] != '\0')
3127 printk("%sHardware name: %s\n",
3128 log_lvl, dump_stack_arch_desc_str);
3129
3130 print_worker_info(log_lvl, current);
3131}
3132
3133/**
3134 * show_regs_print_info - print generic debug info for show_regs()
3135 * @log_lvl: log level
3136 *
3137 * show_regs() implementations can use this function to print out generic
3138 * debug information.
3139 */
3140void show_regs_print_info(const char *log_lvl)
3141{
3142 dump_stack_print_info(log_lvl);
3143
3144 printk("%stask: %p task.stack: %p\n",
3145 log_lvl, current, task_stack_page(current));
3146}
3147
3148#endif
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * linux/kernel/printk.c
4 *
5 * Copyright (C) 1991, 1992 Linus Torvalds
6 *
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
18 */
19
20#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
21
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/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>
50
51#include <linux/uaccess.h>
52#include <asm/sections.h>
53
54#include <trace/events/initcall.h>
55#define CREATE_TRACE_POINTS
56#include <trace/events/printk.h>
57
58#include "printk_ringbuffer.h"
59#include "console_cmdline.h"
60#include "braille.h"
61#include "internal.h"
62
63int 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 */
68};
69EXPORT_SYMBOL_GPL(console_printk);
70
71atomic_t ignore_console_lock_warning __read_mostly = ATOMIC_INIT(0);
72EXPORT_SYMBOL(ignore_console_lock_warning);
73
74/*
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.
77 */
78int oops_in_progress;
79EXPORT_SYMBOL(oops_in_progress);
80
81/*
82 * console_mutex protects console_list updates and console->flags updates.
83 * The flags are synchronized only for consoles that are registered, i.e.
84 * accessible via the console list.
85 */
86static DEFINE_MUTEX(console_mutex);
87
88/*
89 * console_sem protects updates to console->seq and console_suspended,
90 * and also provides serialization for console printing.
91 */
92static DEFINE_SEMAPHORE(console_sem);
93HLIST_HEAD(console_list);
94EXPORT_SYMBOL_GPL(console_list);
95DEFINE_STATIC_SRCU(console_srcu);
96
97/*
98 * System may need to suppress printk message under certain
99 * circumstances, like after kernel panic happens.
100 */
101int __read_mostly suppress_printk;
102
103/*
104 * During panic, heavy printk by other CPUs can delay the
105 * panic and risk deadlock on console resources.
106 */
107static int __read_mostly suppress_panic_printk;
108
109#ifdef CONFIG_LOCKDEP
110static struct lockdep_map console_lock_dep_map = {
111 .name = "console_lock"
112};
113
114void lockdep_assert_console_list_lock_held(void)
115{
116 lockdep_assert_held(&console_mutex);
117}
118EXPORT_SYMBOL(lockdep_assert_console_list_lock_held);
119#endif
120
121#ifdef CONFIG_DEBUG_LOCK_ALLOC
122bool console_srcu_read_lock_is_held(void)
123{
124 return srcu_read_lock_held(&console_srcu);
125}
126EXPORT_SYMBOL(console_srcu_read_lock_is_held);
127#endif
128
129enum devkmsg_log_bits {
130 __DEVKMSG_LOG_BIT_ON = 0,
131 __DEVKMSG_LOG_BIT_OFF,
132 __DEVKMSG_LOG_BIT_LOCK,
133};
134
135enum devkmsg_log_masks {
136 DEVKMSG_LOG_MASK_ON = BIT(__DEVKMSG_LOG_BIT_ON),
137 DEVKMSG_LOG_MASK_OFF = BIT(__DEVKMSG_LOG_BIT_OFF),
138 DEVKMSG_LOG_MASK_LOCK = BIT(__DEVKMSG_LOG_BIT_LOCK),
139};
140
141/* Keep both the 'on' and 'off' bits clear, i.e. ratelimit by default: */
142#define DEVKMSG_LOG_MASK_DEFAULT 0
143
144static unsigned int __read_mostly devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
145
146static int __control_devkmsg(char *str)
147{
148 size_t len;
149
150 if (!str)
151 return -EINVAL;
152
153 len = str_has_prefix(str, "on");
154 if (len) {
155 devkmsg_log = DEVKMSG_LOG_MASK_ON;
156 return len;
157 }
158
159 len = str_has_prefix(str, "off");
160 if (len) {
161 devkmsg_log = DEVKMSG_LOG_MASK_OFF;
162 return len;
163 }
164
165 len = str_has_prefix(str, "ratelimit");
166 if (len) {
167 devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
168 return len;
169 }
170
171 return -EINVAL;
172}
173
174static int __init control_devkmsg(char *str)
175{
176 if (__control_devkmsg(str) < 0) {
177 pr_warn("printk.devkmsg: bad option string '%s'\n", str);
178 return 1;
179 }
180
181 /*
182 * Set sysctl string accordingly:
183 */
184 if (devkmsg_log == DEVKMSG_LOG_MASK_ON)
185 strcpy(devkmsg_log_str, "on");
186 else if (devkmsg_log == DEVKMSG_LOG_MASK_OFF)
187 strcpy(devkmsg_log_str, "off");
188 /* else "ratelimit" which is set by default. */
189
190 /*
191 * Sysctl cannot change it anymore. The kernel command line setting of
192 * this parameter is to force the setting to be permanent throughout the
193 * runtime of the system. This is a precation measure against userspace
194 * trying to be a smarta** and attempting to change it up on us.
195 */
196 devkmsg_log |= DEVKMSG_LOG_MASK_LOCK;
197
198 return 1;
199}
200__setup("printk.devkmsg=", control_devkmsg);
201
202char devkmsg_log_str[DEVKMSG_STR_MAX_SIZE] = "ratelimit";
203#if defined(CONFIG_PRINTK) && defined(CONFIG_SYSCTL)
204int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write,
205 void *buffer, size_t *lenp, loff_t *ppos)
206{
207 char old_str[DEVKMSG_STR_MAX_SIZE];
208 unsigned int old;
209 int err;
210
211 if (write) {
212 if (devkmsg_log & DEVKMSG_LOG_MASK_LOCK)
213 return -EINVAL;
214
215 old = devkmsg_log;
216 strncpy(old_str, devkmsg_log_str, DEVKMSG_STR_MAX_SIZE);
217 }
218
219 err = proc_dostring(table, write, buffer, lenp, ppos);
220 if (err)
221 return err;
222
223 if (write) {
224 err = __control_devkmsg(devkmsg_log_str);
225
226 /*
227 * Do not accept an unknown string OR a known string with
228 * trailing crap...
229 */
230 if (err < 0 || (err + 1 != *lenp)) {
231
232 /* ... and restore old setting. */
233 devkmsg_log = old;
234 strncpy(devkmsg_log_str, old_str, DEVKMSG_STR_MAX_SIZE);
235
236 return -EINVAL;
237 }
238 }
239
240 return 0;
241}
242#endif /* CONFIG_PRINTK && CONFIG_SYSCTL */
243
244/**
245 * console_list_lock - Lock the console list
246 *
247 * For console list or console->flags updates
248 */
249void console_list_lock(void)
250{
251 /*
252 * In unregister_console() and console_force_preferred_locked(),
253 * synchronize_srcu() is called with the console_list_lock held.
254 * Therefore it is not allowed that the console_list_lock is taken
255 * with the srcu_lock held.
256 *
257 * Detecting if this context is really in the read-side critical
258 * section is only possible if the appropriate debug options are
259 * enabled.
260 */
261 WARN_ON_ONCE(debug_lockdep_rcu_enabled() &&
262 srcu_read_lock_held(&console_srcu));
263
264 mutex_lock(&console_mutex);
265}
266EXPORT_SYMBOL(console_list_lock);
267
268/**
269 * console_list_unlock - Unlock the console list
270 *
271 * Counterpart to console_list_lock()
272 */
273void console_list_unlock(void)
274{
275 mutex_unlock(&console_mutex);
276}
277EXPORT_SYMBOL(console_list_unlock);
278
279/**
280 * console_srcu_read_lock - Register a new reader for the
281 * SRCU-protected console list
282 *
283 * Use for_each_console_srcu() to iterate the console list
284 *
285 * Context: Any context.
286 * Return: A cookie to pass to console_srcu_read_unlock().
287 */
288int console_srcu_read_lock(void)
289{
290 return srcu_read_lock_nmisafe(&console_srcu);
291}
292EXPORT_SYMBOL(console_srcu_read_lock);
293
294/**
295 * console_srcu_read_unlock - Unregister an old reader from
296 * the SRCU-protected console list
297 * @cookie: cookie returned from console_srcu_read_lock()
298 *
299 * Counterpart to console_srcu_read_lock()
300 */
301void console_srcu_read_unlock(int cookie)
302{
303 srcu_read_unlock_nmisafe(&console_srcu, cookie);
304}
305EXPORT_SYMBOL(console_srcu_read_unlock);
306
307/*
308 * Helper macros to handle lockdep when locking/unlocking console_sem. We use
309 * macros instead of functions so that _RET_IP_ contains useful information.
310 */
311#define down_console_sem() do { \
312 down(&console_sem);\
313 mutex_acquire(&console_lock_dep_map, 0, 0, _RET_IP_);\
314} while (0)
315
316static int __down_trylock_console_sem(unsigned long ip)
317{
318 int lock_failed;
319 unsigned long flags;
320
321 /*
322 * Here and in __up_console_sem() we need to be in safe mode,
323 * because spindump/WARN/etc from under console ->lock will
324 * deadlock in printk()->down_trylock_console_sem() otherwise.
325 */
326 printk_safe_enter_irqsave(flags);
327 lock_failed = down_trylock(&console_sem);
328 printk_safe_exit_irqrestore(flags);
329
330 if (lock_failed)
331 return 1;
332 mutex_acquire(&console_lock_dep_map, 0, 1, ip);
333 return 0;
334}
335#define down_trylock_console_sem() __down_trylock_console_sem(_RET_IP_)
336
337static void __up_console_sem(unsigned long ip)
338{
339 unsigned long flags;
340
341 mutex_release(&console_lock_dep_map, ip);
342
343 printk_safe_enter_irqsave(flags);
344 up(&console_sem);
345 printk_safe_exit_irqrestore(flags);
346}
347#define up_console_sem() __up_console_sem(_RET_IP_)
348
349static bool panic_in_progress(void)
350{
351 return unlikely(atomic_read(&panic_cpu) != PANIC_CPU_INVALID);
352}
353
354/*
355 * This is used for debugging the mess that is the VT code by
356 * keeping track if we have the console semaphore held. It's
357 * definitely not the perfect debug tool (we don't know if _WE_
358 * hold it and are racing, but it helps tracking those weird code
359 * paths in the console code where we end up in places I want
360 * locked without the console semaphore held).
361 */
362static int console_locked, console_suspended;
363
364/*
365 * Array of consoles built from command line options (console=)
366 */
367
368#define MAX_CMDLINECONSOLES 8
369
370static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
371
372static int preferred_console = -1;
373int console_set_on_cmdline;
374EXPORT_SYMBOL(console_set_on_cmdline);
375
376/* Flag: console code may call schedule() */
377static int console_may_schedule;
378
379enum con_msg_format_flags {
380 MSG_FORMAT_DEFAULT = 0,
381 MSG_FORMAT_SYSLOG = (1 << 0),
382};
383
384static int console_msg_format = MSG_FORMAT_DEFAULT;
385
386/*
387 * The printk log buffer consists of a sequenced collection of records, each
388 * containing variable length message text. Every record also contains its
389 * own meta-data (@info).
390 *
391 * Every record meta-data carries the timestamp in microseconds, as well as
392 * the standard userspace syslog level and syslog facility. The usual kernel
393 * messages use LOG_KERN; userspace-injected messages always carry a matching
394 * syslog facility, by default LOG_USER. The origin of every message can be
395 * reliably determined that way.
396 *
397 * The human readable log message of a record is available in @text, the
398 * length of the message text in @text_len. The stored message is not
399 * terminated.
400 *
401 * Optionally, a record can carry a dictionary of properties (key/value
402 * pairs), to provide userspace with a machine-readable message context.
403 *
404 * Examples for well-defined, commonly used property names are:
405 * DEVICE=b12:8 device identifier
406 * b12:8 block dev_t
407 * c127:3 char dev_t
408 * n8 netdev ifindex
409 * +sound:card0 subsystem:devname
410 * SUBSYSTEM=pci driver-core subsystem name
411 *
412 * Valid characters in property names are [a-zA-Z0-9.-_]. Property names
413 * and values are terminated by a '\0' character.
414 *
415 * Example of record values:
416 * record.text_buf = "it's a line" (unterminated)
417 * record.info.seq = 56
418 * record.info.ts_nsec = 36863
419 * record.info.text_len = 11
420 * record.info.facility = 0 (LOG_KERN)
421 * record.info.flags = 0
422 * record.info.level = 3 (LOG_ERR)
423 * record.info.caller_id = 299 (task 299)
424 * record.info.dev_info.subsystem = "pci" (terminated)
425 * record.info.dev_info.device = "+pci:0000:00:01.0" (terminated)
426 *
427 * The 'struct printk_info' buffer must never be directly exported to
428 * userspace, it is a kernel-private implementation detail that might
429 * need to be changed in the future, when the requirements change.
430 *
431 * /dev/kmsg exports the structured data in the following line format:
432 * "<level>,<sequnum>,<timestamp>,<contflag>[,additional_values, ... ];<message text>\n"
433 *
434 * Users of the export format should ignore possible additional values
435 * separated by ',', and find the message after the ';' character.
436 *
437 * The optional key/value pairs are attached as continuation lines starting
438 * with a space character and terminated by a newline. All possible
439 * non-prinatable characters are escaped in the "\xff" notation.
440 */
441
442/* syslog_lock protects syslog_* variables and write access to clear_seq. */
443static DEFINE_MUTEX(syslog_lock);
444
445#ifdef CONFIG_PRINTK
446DECLARE_WAIT_QUEUE_HEAD(log_wait);
447/* All 3 protected by @syslog_lock. */
448/* the next printk record to read by syslog(READ) or /proc/kmsg */
449static u64 syslog_seq;
450static size_t syslog_partial;
451static bool syslog_time;
452
453struct latched_seq {
454 seqcount_latch_t latch;
455 u64 val[2];
456};
457
458/*
459 * The next printk record to read after the last 'clear' command. There are
460 * two copies (updated with seqcount_latch) so that reads can locklessly
461 * access a valid value. Writers are synchronized by @syslog_lock.
462 */
463static struct latched_seq clear_seq = {
464 .latch = SEQCNT_LATCH_ZERO(clear_seq.latch),
465 .val[0] = 0,
466 .val[1] = 0,
467};
468
469#ifdef CONFIG_PRINTK_CALLER
470#define PREFIX_MAX 48
471#else
472#define PREFIX_MAX 32
473#endif
474
475/* the maximum size of a formatted record (i.e. with prefix added per line) */
476#define CONSOLE_LOG_MAX 1024
477
478/* the maximum size for a dropped text message */
479#define DROPPED_TEXT_MAX 64
480
481/* the maximum size allowed to be reserved for a record */
482#define LOG_LINE_MAX (CONSOLE_LOG_MAX - PREFIX_MAX)
483
484#define LOG_LEVEL(v) ((v) & 0x07)
485#define LOG_FACILITY(v) ((v) >> 3 & 0xff)
486
487/* record buffer */
488#define LOG_ALIGN __alignof__(unsigned long)
489#define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
490#define LOG_BUF_LEN_MAX (u32)(1 << 31)
491static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
492static char *log_buf = __log_buf;
493static u32 log_buf_len = __LOG_BUF_LEN;
494
495/*
496 * Define the average message size. This only affects the number of
497 * descriptors that will be available. Underestimating is better than
498 * overestimating (too many available descriptors is better than not enough).
499 */
500#define PRB_AVGBITS 5 /* 32 character average length */
501
502#if CONFIG_LOG_BUF_SHIFT <= PRB_AVGBITS
503#error CONFIG_LOG_BUF_SHIFT value too small.
504#endif
505_DEFINE_PRINTKRB(printk_rb_static, CONFIG_LOG_BUF_SHIFT - PRB_AVGBITS,
506 PRB_AVGBITS, &__log_buf[0]);
507
508static struct printk_ringbuffer printk_rb_dynamic;
509
510static struct printk_ringbuffer *prb = &printk_rb_static;
511
512/*
513 * We cannot access per-CPU data (e.g. per-CPU flush irq_work) before
514 * per_cpu_areas are initialised. This variable is set to true when
515 * it's safe to access per-CPU data.
516 */
517static bool __printk_percpu_data_ready __ro_after_init;
518
519bool printk_percpu_data_ready(void)
520{
521 return __printk_percpu_data_ready;
522}
523
524/* Must be called under syslog_lock. */
525static void latched_seq_write(struct latched_seq *ls, u64 val)
526{
527 raw_write_seqcount_latch(&ls->latch);
528 ls->val[0] = val;
529 raw_write_seqcount_latch(&ls->latch);
530 ls->val[1] = val;
531}
532
533/* Can be called from any context. */
534static u64 latched_seq_read_nolock(struct latched_seq *ls)
535{
536 unsigned int seq;
537 unsigned int idx;
538 u64 val;
539
540 do {
541 seq = raw_read_seqcount_latch(&ls->latch);
542 idx = seq & 0x1;
543 val = ls->val[idx];
544 } while (read_seqcount_latch_retry(&ls->latch, seq));
545
546 return val;
547}
548
549/* Return log buffer address */
550char *log_buf_addr_get(void)
551{
552 return log_buf;
553}
554
555/* Return log buffer size */
556u32 log_buf_len_get(void)
557{
558 return log_buf_len;
559}
560
561/*
562 * Define how much of the log buffer we could take at maximum. The value
563 * must be greater than two. Note that only half of the buffer is available
564 * when the index points to the middle.
565 */
566#define MAX_LOG_TAKE_PART 4
567static const char trunc_msg[] = "<truncated>";
568
569static void truncate_msg(u16 *text_len, u16 *trunc_msg_len)
570{
571 /*
572 * The message should not take the whole buffer. Otherwise, it might
573 * get removed too soon.
574 */
575 u32 max_text_len = log_buf_len / MAX_LOG_TAKE_PART;
576
577 if (*text_len > max_text_len)
578 *text_len = max_text_len;
579
580 /* enable the warning message (if there is room) */
581 *trunc_msg_len = strlen(trunc_msg);
582 if (*text_len >= *trunc_msg_len)
583 *text_len -= *trunc_msg_len;
584 else
585 *trunc_msg_len = 0;
586}
587
588int dmesg_restrict = IS_ENABLED(CONFIG_SECURITY_DMESG_RESTRICT);
589
590static int syslog_action_restricted(int type)
591{
592 if (dmesg_restrict)
593 return 1;
594 /*
595 * Unless restricted, we allow "read all" and "get buffer size"
596 * for everybody.
597 */
598 return type != SYSLOG_ACTION_READ_ALL &&
599 type != SYSLOG_ACTION_SIZE_BUFFER;
600}
601
602static int check_syslog_permissions(int type, int source)
603{
604 /*
605 * If this is from /proc/kmsg and we've already opened it, then we've
606 * already done the capabilities checks at open time.
607 */
608 if (source == SYSLOG_FROM_PROC && type != SYSLOG_ACTION_OPEN)
609 goto ok;
610
611 if (syslog_action_restricted(type)) {
612 if (capable(CAP_SYSLOG))
613 goto ok;
614 /*
615 * For historical reasons, accept CAP_SYS_ADMIN too, with
616 * a warning.
617 */
618 if (capable(CAP_SYS_ADMIN)) {
619 pr_warn_once("%s (%d): Attempt to access syslog with "
620 "CAP_SYS_ADMIN but no CAP_SYSLOG "
621 "(deprecated).\n",
622 current->comm, task_pid_nr(current));
623 goto ok;
624 }
625 return -EPERM;
626 }
627ok:
628 return security_syslog(type);
629}
630
631static void append_char(char **pp, char *e, char c)
632{
633 if (*pp < e)
634 *(*pp)++ = c;
635}
636
637static ssize_t info_print_ext_header(char *buf, size_t size,
638 struct printk_info *info)
639{
640 u64 ts_usec = info->ts_nsec;
641 char caller[20];
642#ifdef CONFIG_PRINTK_CALLER
643 u32 id = info->caller_id;
644
645 snprintf(caller, sizeof(caller), ",caller=%c%u",
646 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
647#else
648 caller[0] = '\0';
649#endif
650
651 do_div(ts_usec, 1000);
652
653 return scnprintf(buf, size, "%u,%llu,%llu,%c%s;",
654 (info->facility << 3) | info->level, info->seq,
655 ts_usec, info->flags & LOG_CONT ? 'c' : '-', caller);
656}
657
658static ssize_t msg_add_ext_text(char *buf, size_t size,
659 const char *text, size_t text_len,
660 unsigned char endc)
661{
662 char *p = buf, *e = buf + size;
663 size_t i;
664
665 /* escape non-printable characters */
666 for (i = 0; i < text_len; i++) {
667 unsigned char c = text[i];
668
669 if (c < ' ' || c >= 127 || c == '\\')
670 p += scnprintf(p, e - p, "\\x%02x", c);
671 else
672 append_char(&p, e, c);
673 }
674 append_char(&p, e, endc);
675
676 return p - buf;
677}
678
679static ssize_t msg_add_dict_text(char *buf, size_t size,
680 const char *key, const char *val)
681{
682 size_t val_len = strlen(val);
683 ssize_t len;
684
685 if (!val_len)
686 return 0;
687
688 len = msg_add_ext_text(buf, size, "", 0, ' '); /* dict prefix */
689 len += msg_add_ext_text(buf + len, size - len, key, strlen(key), '=');
690 len += msg_add_ext_text(buf + len, size - len, val, val_len, '\n');
691
692 return len;
693}
694
695static ssize_t msg_print_ext_body(char *buf, size_t size,
696 char *text, size_t text_len,
697 struct dev_printk_info *dev_info)
698{
699 ssize_t len;
700
701 len = msg_add_ext_text(buf, size, text, text_len, '\n');
702
703 if (!dev_info)
704 goto out;
705
706 len += msg_add_dict_text(buf + len, size - len, "SUBSYSTEM",
707 dev_info->subsystem);
708 len += msg_add_dict_text(buf + len, size - len, "DEVICE",
709 dev_info->device);
710out:
711 return len;
712}
713
714/* /dev/kmsg - userspace message inject/listen interface */
715struct devkmsg_user {
716 atomic64_t seq;
717 struct ratelimit_state rs;
718 struct mutex lock;
719 char buf[CONSOLE_EXT_LOG_MAX];
720
721 struct printk_info info;
722 char text_buf[CONSOLE_EXT_LOG_MAX];
723 struct printk_record record;
724};
725
726static __printf(3, 4) __cold
727int devkmsg_emit(int facility, int level, const char *fmt, ...)
728{
729 va_list args;
730 int r;
731
732 va_start(args, fmt);
733 r = vprintk_emit(facility, level, NULL, fmt, args);
734 va_end(args);
735
736 return r;
737}
738
739static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
740{
741 char *buf, *line;
742 int level = default_message_loglevel;
743 int facility = 1; /* LOG_USER */
744 struct file *file = iocb->ki_filp;
745 struct devkmsg_user *user = file->private_data;
746 size_t len = iov_iter_count(from);
747 ssize_t ret = len;
748
749 if (!user || len > LOG_LINE_MAX)
750 return -EINVAL;
751
752 /* Ignore when user logging is disabled. */
753 if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
754 return len;
755
756 /* Ratelimit when not explicitly enabled. */
757 if (!(devkmsg_log & DEVKMSG_LOG_MASK_ON)) {
758 if (!___ratelimit(&user->rs, current->comm))
759 return ret;
760 }
761
762 buf = kmalloc(len+1, GFP_KERNEL);
763 if (buf == NULL)
764 return -ENOMEM;
765
766 buf[len] = '\0';
767 if (!copy_from_iter_full(buf, len, from)) {
768 kfree(buf);
769 return -EFAULT;
770 }
771
772 /*
773 * Extract and skip the syslog prefix <[0-9]*>. Coming from userspace
774 * the decimal value represents 32bit, the lower 3 bit are the log
775 * level, the rest are the log facility.
776 *
777 * If no prefix or no userspace facility is specified, we
778 * enforce LOG_USER, to be able to reliably distinguish
779 * kernel-generated messages from userspace-injected ones.
780 */
781 line = buf;
782 if (line[0] == '<') {
783 char *endp = NULL;
784 unsigned int u;
785
786 u = simple_strtoul(line + 1, &endp, 10);
787 if (endp && endp[0] == '>') {
788 level = LOG_LEVEL(u);
789 if (LOG_FACILITY(u) != 0)
790 facility = LOG_FACILITY(u);
791 endp++;
792 line = endp;
793 }
794 }
795
796 devkmsg_emit(facility, level, "%s", line);
797 kfree(buf);
798 return ret;
799}
800
801static ssize_t devkmsg_read(struct file *file, char __user *buf,
802 size_t count, loff_t *ppos)
803{
804 struct devkmsg_user *user = file->private_data;
805 struct printk_record *r = &user->record;
806 size_t len;
807 ssize_t ret;
808
809 if (!user)
810 return -EBADF;
811
812 ret = mutex_lock_interruptible(&user->lock);
813 if (ret)
814 return ret;
815
816 if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {
817 if (file->f_flags & O_NONBLOCK) {
818 ret = -EAGAIN;
819 goto out;
820 }
821
822 /*
823 * Guarantee this task is visible on the waitqueue before
824 * checking the wake condition.
825 *
826 * The full memory barrier within set_current_state() of
827 * prepare_to_wait_event() pairs with the full memory barrier
828 * within wq_has_sleeper().
829 *
830 * This pairs with __wake_up_klogd:A.
831 */
832 ret = wait_event_interruptible(log_wait,
833 prb_read_valid(prb,
834 atomic64_read(&user->seq), r)); /* LMM(devkmsg_read:A) */
835 if (ret)
836 goto out;
837 }
838
839 if (r->info->seq != atomic64_read(&user->seq)) {
840 /* our last seen message is gone, return error and reset */
841 atomic64_set(&user->seq, r->info->seq);
842 ret = -EPIPE;
843 goto out;
844 }
845
846 len = info_print_ext_header(user->buf, sizeof(user->buf), r->info);
847 len += msg_print_ext_body(user->buf + len, sizeof(user->buf) - len,
848 &r->text_buf[0], r->info->text_len,
849 &r->info->dev_info);
850
851 atomic64_set(&user->seq, r->info->seq + 1);
852
853 if (len > count) {
854 ret = -EINVAL;
855 goto out;
856 }
857
858 if (copy_to_user(buf, user->buf, len)) {
859 ret = -EFAULT;
860 goto out;
861 }
862 ret = len;
863out:
864 mutex_unlock(&user->lock);
865 return ret;
866}
867
868/*
869 * Be careful when modifying this function!!!
870 *
871 * Only few operations are supported because the device works only with the
872 * entire variable length messages (records). Non-standard values are
873 * returned in the other cases and has been this way for quite some time.
874 * User space applications might depend on this behavior.
875 */
876static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
877{
878 struct devkmsg_user *user = file->private_data;
879 loff_t ret = 0;
880
881 if (!user)
882 return -EBADF;
883 if (offset)
884 return -ESPIPE;
885
886 switch (whence) {
887 case SEEK_SET:
888 /* the first record */
889 atomic64_set(&user->seq, prb_first_valid_seq(prb));
890 break;
891 case SEEK_DATA:
892 /*
893 * The first record after the last SYSLOG_ACTION_CLEAR,
894 * like issued by 'dmesg -c'. Reading /dev/kmsg itself
895 * changes no global state, and does not clear anything.
896 */
897 atomic64_set(&user->seq, latched_seq_read_nolock(&clear_seq));
898 break;
899 case SEEK_END:
900 /* after the last record */
901 atomic64_set(&user->seq, prb_next_seq(prb));
902 break;
903 default:
904 ret = -EINVAL;
905 }
906 return ret;
907}
908
909static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
910{
911 struct devkmsg_user *user = file->private_data;
912 struct printk_info info;
913 __poll_t ret = 0;
914
915 if (!user)
916 return EPOLLERR|EPOLLNVAL;
917
918 poll_wait(file, &log_wait, wait);
919
920 if (prb_read_valid_info(prb, atomic64_read(&user->seq), &info, NULL)) {
921 /* return error when data has vanished underneath us */
922 if (info.seq != atomic64_read(&user->seq))
923 ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;
924 else
925 ret = EPOLLIN|EPOLLRDNORM;
926 }
927
928 return ret;
929}
930
931static int devkmsg_open(struct inode *inode, struct file *file)
932{
933 struct devkmsg_user *user;
934 int err;
935
936 if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
937 return -EPERM;
938
939 /* write-only does not need any file context */
940 if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
941 err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
942 SYSLOG_FROM_READER);
943 if (err)
944 return err;
945 }
946
947 user = kvmalloc(sizeof(struct devkmsg_user), GFP_KERNEL);
948 if (!user)
949 return -ENOMEM;
950
951 ratelimit_default_init(&user->rs);
952 ratelimit_set_flags(&user->rs, RATELIMIT_MSG_ON_RELEASE);
953
954 mutex_init(&user->lock);
955
956 prb_rec_init_rd(&user->record, &user->info,
957 &user->text_buf[0], sizeof(user->text_buf));
958
959 atomic64_set(&user->seq, prb_first_valid_seq(prb));
960
961 file->private_data = user;
962 return 0;
963}
964
965static int devkmsg_release(struct inode *inode, struct file *file)
966{
967 struct devkmsg_user *user = file->private_data;
968
969 if (!user)
970 return 0;
971
972 ratelimit_state_exit(&user->rs);
973
974 mutex_destroy(&user->lock);
975 kvfree(user);
976 return 0;
977}
978
979const struct file_operations kmsg_fops = {
980 .open = devkmsg_open,
981 .read = devkmsg_read,
982 .write_iter = devkmsg_write,
983 .llseek = devkmsg_llseek,
984 .poll = devkmsg_poll,
985 .release = devkmsg_release,
986};
987
988#ifdef CONFIG_CRASH_CORE
989/*
990 * This appends the listed symbols to /proc/vmcore
991 *
992 * /proc/vmcore is used by various utilities, like crash and makedumpfile to
993 * obtain access to symbols that are otherwise very difficult to locate. These
994 * symbols are specifically used so that utilities can access and extract the
995 * dmesg log from a vmcore file after a crash.
996 */
997void log_buf_vmcoreinfo_setup(void)
998{
999 struct dev_printk_info *dev_info = NULL;
1000
1001 VMCOREINFO_SYMBOL(prb);
1002 VMCOREINFO_SYMBOL(printk_rb_static);
1003 VMCOREINFO_SYMBOL(clear_seq);
1004
1005 /*
1006 * Export struct size and field offsets. User space tools can
1007 * parse it and detect any changes to structure down the line.
1008 */
1009
1010 VMCOREINFO_STRUCT_SIZE(printk_ringbuffer);
1011 VMCOREINFO_OFFSET(printk_ringbuffer, desc_ring);
1012 VMCOREINFO_OFFSET(printk_ringbuffer, text_data_ring);
1013 VMCOREINFO_OFFSET(printk_ringbuffer, fail);
1014
1015 VMCOREINFO_STRUCT_SIZE(prb_desc_ring);
1016 VMCOREINFO_OFFSET(prb_desc_ring, count_bits);
1017 VMCOREINFO_OFFSET(prb_desc_ring, descs);
1018 VMCOREINFO_OFFSET(prb_desc_ring, infos);
1019 VMCOREINFO_OFFSET(prb_desc_ring, head_id);
1020 VMCOREINFO_OFFSET(prb_desc_ring, tail_id);
1021
1022 VMCOREINFO_STRUCT_SIZE(prb_desc);
1023 VMCOREINFO_OFFSET(prb_desc, state_var);
1024 VMCOREINFO_OFFSET(prb_desc, text_blk_lpos);
1025
1026 VMCOREINFO_STRUCT_SIZE(prb_data_blk_lpos);
1027 VMCOREINFO_OFFSET(prb_data_blk_lpos, begin);
1028 VMCOREINFO_OFFSET(prb_data_blk_lpos, next);
1029
1030 VMCOREINFO_STRUCT_SIZE(printk_info);
1031 VMCOREINFO_OFFSET(printk_info, seq);
1032 VMCOREINFO_OFFSET(printk_info, ts_nsec);
1033 VMCOREINFO_OFFSET(printk_info, text_len);
1034 VMCOREINFO_OFFSET(printk_info, caller_id);
1035 VMCOREINFO_OFFSET(printk_info, dev_info);
1036
1037 VMCOREINFO_STRUCT_SIZE(dev_printk_info);
1038 VMCOREINFO_OFFSET(dev_printk_info, subsystem);
1039 VMCOREINFO_LENGTH(printk_info_subsystem, sizeof(dev_info->subsystem));
1040 VMCOREINFO_OFFSET(dev_printk_info, device);
1041 VMCOREINFO_LENGTH(printk_info_device, sizeof(dev_info->device));
1042
1043 VMCOREINFO_STRUCT_SIZE(prb_data_ring);
1044 VMCOREINFO_OFFSET(prb_data_ring, size_bits);
1045 VMCOREINFO_OFFSET(prb_data_ring, data);
1046 VMCOREINFO_OFFSET(prb_data_ring, head_lpos);
1047 VMCOREINFO_OFFSET(prb_data_ring, tail_lpos);
1048
1049 VMCOREINFO_SIZE(atomic_long_t);
1050 VMCOREINFO_TYPE_OFFSET(atomic_long_t, counter);
1051
1052 VMCOREINFO_STRUCT_SIZE(latched_seq);
1053 VMCOREINFO_OFFSET(latched_seq, val);
1054}
1055#endif
1056
1057/* requested log_buf_len from kernel cmdline */
1058static unsigned long __initdata new_log_buf_len;
1059
1060/* we practice scaling the ring buffer by powers of 2 */
1061static void __init log_buf_len_update(u64 size)
1062{
1063 if (size > (u64)LOG_BUF_LEN_MAX) {
1064 size = (u64)LOG_BUF_LEN_MAX;
1065 pr_err("log_buf over 2G is not supported.\n");
1066 }
1067
1068 if (size)
1069 size = roundup_pow_of_two(size);
1070 if (size > log_buf_len)
1071 new_log_buf_len = (unsigned long)size;
1072}
1073
1074/* save requested log_buf_len since it's too early to process it */
1075static int __init log_buf_len_setup(char *str)
1076{
1077 u64 size;
1078
1079 if (!str)
1080 return -EINVAL;
1081
1082 size = memparse(str, &str);
1083
1084 log_buf_len_update(size);
1085
1086 return 0;
1087}
1088early_param("log_buf_len", log_buf_len_setup);
1089
1090#ifdef CONFIG_SMP
1091#define __LOG_CPU_MAX_BUF_LEN (1 << CONFIG_LOG_CPU_MAX_BUF_SHIFT)
1092
1093static void __init log_buf_add_cpu(void)
1094{
1095 unsigned int cpu_extra;
1096
1097 /*
1098 * archs should set up cpu_possible_bits properly with
1099 * set_cpu_possible() after setup_arch() but just in
1100 * case lets ensure this is valid.
1101 */
1102 if (num_possible_cpus() == 1)
1103 return;
1104
1105 cpu_extra = (num_possible_cpus() - 1) * __LOG_CPU_MAX_BUF_LEN;
1106
1107 /* by default this will only continue through for large > 64 CPUs */
1108 if (cpu_extra <= __LOG_BUF_LEN / 2)
1109 return;
1110
1111 pr_info("log_buf_len individual max cpu contribution: %d bytes\n",
1112 __LOG_CPU_MAX_BUF_LEN);
1113 pr_info("log_buf_len total cpu_extra contributions: %d bytes\n",
1114 cpu_extra);
1115 pr_info("log_buf_len min size: %d bytes\n", __LOG_BUF_LEN);
1116
1117 log_buf_len_update(cpu_extra + __LOG_BUF_LEN);
1118}
1119#else /* !CONFIG_SMP */
1120static inline void log_buf_add_cpu(void) {}
1121#endif /* CONFIG_SMP */
1122
1123static void __init set_percpu_data_ready(void)
1124{
1125 __printk_percpu_data_ready = true;
1126}
1127
1128static unsigned int __init add_to_rb(struct printk_ringbuffer *rb,
1129 struct printk_record *r)
1130{
1131 struct prb_reserved_entry e;
1132 struct printk_record dest_r;
1133
1134 prb_rec_init_wr(&dest_r, r->info->text_len);
1135
1136 if (!prb_reserve(&e, rb, &dest_r))
1137 return 0;
1138
1139 memcpy(&dest_r.text_buf[0], &r->text_buf[0], r->info->text_len);
1140 dest_r.info->text_len = r->info->text_len;
1141 dest_r.info->facility = r->info->facility;
1142 dest_r.info->level = r->info->level;
1143 dest_r.info->flags = r->info->flags;
1144 dest_r.info->ts_nsec = r->info->ts_nsec;
1145 dest_r.info->caller_id = r->info->caller_id;
1146 memcpy(&dest_r.info->dev_info, &r->info->dev_info, sizeof(dest_r.info->dev_info));
1147
1148 prb_final_commit(&e);
1149
1150 return prb_record_text_space(&e);
1151}
1152
1153static char setup_text_buf[LOG_LINE_MAX] __initdata;
1154
1155void __init setup_log_buf(int early)
1156{
1157 struct printk_info *new_infos;
1158 unsigned int new_descs_count;
1159 struct prb_desc *new_descs;
1160 struct printk_info info;
1161 struct printk_record r;
1162 unsigned int text_size;
1163 size_t new_descs_size;
1164 size_t new_infos_size;
1165 unsigned long flags;
1166 char *new_log_buf;
1167 unsigned int free;
1168 u64 seq;
1169
1170 /*
1171 * Some archs call setup_log_buf() multiple times - first is very
1172 * early, e.g. from setup_arch(), and second - when percpu_areas
1173 * are initialised.
1174 */
1175 if (!early)
1176 set_percpu_data_ready();
1177
1178 if (log_buf != __log_buf)
1179 return;
1180
1181 if (!early && !new_log_buf_len)
1182 log_buf_add_cpu();
1183
1184 if (!new_log_buf_len)
1185 return;
1186
1187 new_descs_count = new_log_buf_len >> PRB_AVGBITS;
1188 if (new_descs_count == 0) {
1189 pr_err("new_log_buf_len: %lu too small\n", new_log_buf_len);
1190 return;
1191 }
1192
1193 new_log_buf = memblock_alloc(new_log_buf_len, LOG_ALIGN);
1194 if (unlikely(!new_log_buf)) {
1195 pr_err("log_buf_len: %lu text bytes not available\n",
1196 new_log_buf_len);
1197 return;
1198 }
1199
1200 new_descs_size = new_descs_count * sizeof(struct prb_desc);
1201 new_descs = memblock_alloc(new_descs_size, LOG_ALIGN);
1202 if (unlikely(!new_descs)) {
1203 pr_err("log_buf_len: %zu desc bytes not available\n",
1204 new_descs_size);
1205 goto err_free_log_buf;
1206 }
1207
1208 new_infos_size = new_descs_count * sizeof(struct printk_info);
1209 new_infos = memblock_alloc(new_infos_size, LOG_ALIGN);
1210 if (unlikely(!new_infos)) {
1211 pr_err("log_buf_len: %zu info bytes not available\n",
1212 new_infos_size);
1213 goto err_free_descs;
1214 }
1215
1216 prb_rec_init_rd(&r, &info, &setup_text_buf[0], sizeof(setup_text_buf));
1217
1218 prb_init(&printk_rb_dynamic,
1219 new_log_buf, ilog2(new_log_buf_len),
1220 new_descs, ilog2(new_descs_count),
1221 new_infos);
1222
1223 local_irq_save(flags);
1224
1225 log_buf_len = new_log_buf_len;
1226 log_buf = new_log_buf;
1227 new_log_buf_len = 0;
1228
1229 free = __LOG_BUF_LEN;
1230 prb_for_each_record(0, &printk_rb_static, seq, &r) {
1231 text_size = add_to_rb(&printk_rb_dynamic, &r);
1232 if (text_size > free)
1233 free = 0;
1234 else
1235 free -= text_size;
1236 }
1237
1238 prb = &printk_rb_dynamic;
1239
1240 local_irq_restore(flags);
1241
1242 /*
1243 * Copy any remaining messages that might have appeared from
1244 * NMI context after copying but before switching to the
1245 * dynamic buffer.
1246 */
1247 prb_for_each_record(seq, &printk_rb_static, seq, &r) {
1248 text_size = add_to_rb(&printk_rb_dynamic, &r);
1249 if (text_size > free)
1250 free = 0;
1251 else
1252 free -= text_size;
1253 }
1254
1255 if (seq != prb_next_seq(&printk_rb_static)) {
1256 pr_err("dropped %llu messages\n",
1257 prb_next_seq(&printk_rb_static) - seq);
1258 }
1259
1260 pr_info("log_buf_len: %u bytes\n", log_buf_len);
1261 pr_info("early log buf free: %u(%u%%)\n",
1262 free, (free * 100) / __LOG_BUF_LEN);
1263 return;
1264
1265err_free_descs:
1266 memblock_free(new_descs, new_descs_size);
1267err_free_log_buf:
1268 memblock_free(new_log_buf, new_log_buf_len);
1269}
1270
1271static bool __read_mostly ignore_loglevel;
1272
1273static int __init ignore_loglevel_setup(char *str)
1274{
1275 ignore_loglevel = true;
1276 pr_info("debug: ignoring loglevel setting.\n");
1277
1278 return 0;
1279}
1280
1281early_param("ignore_loglevel", ignore_loglevel_setup);
1282module_param(ignore_loglevel, bool, S_IRUGO | S_IWUSR);
1283MODULE_PARM_DESC(ignore_loglevel,
1284 "ignore loglevel setting (prints all kernel messages to the console)");
1285
1286static bool suppress_message_printing(int level)
1287{
1288 return (level >= console_loglevel && !ignore_loglevel);
1289}
1290
1291#ifdef CONFIG_BOOT_PRINTK_DELAY
1292
1293static int boot_delay; /* msecs delay after each printk during bootup */
1294static unsigned long long loops_per_msec; /* based on boot_delay */
1295
1296static int __init boot_delay_setup(char *str)
1297{
1298 unsigned long lpj;
1299
1300 lpj = preset_lpj ? preset_lpj : 1000000; /* some guess */
1301 loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
1302
1303 get_option(&str, &boot_delay);
1304 if (boot_delay > 10 * 1000)
1305 boot_delay = 0;
1306
1307 pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
1308 "HZ: %d, loops_per_msec: %llu\n",
1309 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
1310 return 0;
1311}
1312early_param("boot_delay", boot_delay_setup);
1313
1314static void boot_delay_msec(int level)
1315{
1316 unsigned long long k;
1317 unsigned long timeout;
1318
1319 if ((boot_delay == 0 || system_state >= SYSTEM_RUNNING)
1320 || suppress_message_printing(level)) {
1321 return;
1322 }
1323
1324 k = (unsigned long long)loops_per_msec * boot_delay;
1325
1326 timeout = jiffies + msecs_to_jiffies(boot_delay);
1327 while (k) {
1328 k--;
1329 cpu_relax();
1330 /*
1331 * use (volatile) jiffies to prevent
1332 * compiler reduction; loop termination via jiffies
1333 * is secondary and may or may not happen.
1334 */
1335 if (time_after(jiffies, timeout))
1336 break;
1337 touch_nmi_watchdog();
1338 }
1339}
1340#else
1341static inline void boot_delay_msec(int level)
1342{
1343}
1344#endif
1345
1346static bool printk_time = IS_ENABLED(CONFIG_PRINTK_TIME);
1347module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
1348
1349static size_t print_syslog(unsigned int level, char *buf)
1350{
1351 return sprintf(buf, "<%u>", level);
1352}
1353
1354static size_t print_time(u64 ts, char *buf)
1355{
1356 unsigned long rem_nsec = do_div(ts, 1000000000);
1357
1358 return sprintf(buf, "[%5lu.%06lu]",
1359 (unsigned long)ts, rem_nsec / 1000);
1360}
1361
1362#ifdef CONFIG_PRINTK_CALLER
1363static size_t print_caller(u32 id, char *buf)
1364{
1365 char caller[12];
1366
1367 snprintf(caller, sizeof(caller), "%c%u",
1368 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
1369 return sprintf(buf, "[%6s]", caller);
1370}
1371#else
1372#define print_caller(id, buf) 0
1373#endif
1374
1375static size_t info_print_prefix(const struct printk_info *info, bool syslog,
1376 bool time, char *buf)
1377{
1378 size_t len = 0;
1379
1380 if (syslog)
1381 len = print_syslog((info->facility << 3) | info->level, buf);
1382
1383 if (time)
1384 len += print_time(info->ts_nsec, buf + len);
1385
1386 len += print_caller(info->caller_id, buf + len);
1387
1388 if (IS_ENABLED(CONFIG_PRINTK_CALLER) || time) {
1389 buf[len++] = ' ';
1390 buf[len] = '\0';
1391 }
1392
1393 return len;
1394}
1395
1396/*
1397 * Prepare the record for printing. The text is shifted within the given
1398 * buffer to avoid a need for another one. The following operations are
1399 * done:
1400 *
1401 * - Add prefix for each line.
1402 * - Drop truncated lines that no longer fit into the buffer.
1403 * - Add the trailing newline that has been removed in vprintk_store().
1404 * - Add a string terminator.
1405 *
1406 * Since the produced string is always terminated, the maximum possible
1407 * return value is @r->text_buf_size - 1;
1408 *
1409 * Return: The length of the updated/prepared text, including the added
1410 * prefixes and the newline. The terminator is not counted. The dropped
1411 * line(s) are not counted.
1412 */
1413static size_t record_print_text(struct printk_record *r, bool syslog,
1414 bool time)
1415{
1416 size_t text_len = r->info->text_len;
1417 size_t buf_size = r->text_buf_size;
1418 char *text = r->text_buf;
1419 char prefix[PREFIX_MAX];
1420 bool truncated = false;
1421 size_t prefix_len;
1422 size_t line_len;
1423 size_t len = 0;
1424 char *next;
1425
1426 /*
1427 * If the message was truncated because the buffer was not large
1428 * enough, treat the available text as if it were the full text.
1429 */
1430 if (text_len > buf_size)
1431 text_len = buf_size;
1432
1433 prefix_len = info_print_prefix(r->info, syslog, time, prefix);
1434
1435 /*
1436 * @text_len: bytes of unprocessed text
1437 * @line_len: bytes of current line _without_ newline
1438 * @text: pointer to beginning of current line
1439 * @len: number of bytes prepared in r->text_buf
1440 */
1441 for (;;) {
1442 next = memchr(text, '\n', text_len);
1443 if (next) {
1444 line_len = next - text;
1445 } else {
1446 /* Drop truncated line(s). */
1447 if (truncated)
1448 break;
1449 line_len = text_len;
1450 }
1451
1452 /*
1453 * Truncate the text if there is not enough space to add the
1454 * prefix and a trailing newline and a terminator.
1455 */
1456 if (len + prefix_len + text_len + 1 + 1 > buf_size) {
1457 /* Drop even the current line if no space. */
1458 if (len + prefix_len + line_len + 1 + 1 > buf_size)
1459 break;
1460
1461 text_len = buf_size - len - prefix_len - 1 - 1;
1462 truncated = true;
1463 }
1464
1465 memmove(text + prefix_len, text, text_len);
1466 memcpy(text, prefix, prefix_len);
1467
1468 /*
1469 * Increment the prepared length to include the text and
1470 * prefix that were just moved+copied. Also increment for the
1471 * newline at the end of this line. If this is the last line,
1472 * there is no newline, but it will be added immediately below.
1473 */
1474 len += prefix_len + line_len + 1;
1475 if (text_len == line_len) {
1476 /*
1477 * This is the last line. Add the trailing newline
1478 * removed in vprintk_store().
1479 */
1480 text[prefix_len + line_len] = '\n';
1481 break;
1482 }
1483
1484 /*
1485 * Advance beyond the added prefix and the related line with
1486 * its newline.
1487 */
1488 text += prefix_len + line_len + 1;
1489
1490 /*
1491 * The remaining text has only decreased by the line with its
1492 * newline.
1493 *
1494 * Note that @text_len can become zero. It happens when @text
1495 * ended with a newline (either due to truncation or the
1496 * original string ending with "\n\n"). The loop is correctly
1497 * repeated and (if not truncated) an empty line with a prefix
1498 * will be prepared.
1499 */
1500 text_len -= line_len + 1;
1501 }
1502
1503 /*
1504 * If a buffer was provided, it will be terminated. Space for the
1505 * string terminator is guaranteed to be available. The terminator is
1506 * not counted in the return value.
1507 */
1508 if (buf_size > 0)
1509 r->text_buf[len] = 0;
1510
1511 return len;
1512}
1513
1514static size_t get_record_print_text_size(struct printk_info *info,
1515 unsigned int line_count,
1516 bool syslog, bool time)
1517{
1518 char prefix[PREFIX_MAX];
1519 size_t prefix_len;
1520
1521 prefix_len = info_print_prefix(info, syslog, time, prefix);
1522
1523 /*
1524 * Each line will be preceded with a prefix. The intermediate
1525 * newlines are already within the text, but a final trailing
1526 * newline will be added.
1527 */
1528 return ((prefix_len * line_count) + info->text_len + 1);
1529}
1530
1531/*
1532 * Beginning with @start_seq, find the first record where it and all following
1533 * records up to (but not including) @max_seq fit into @size.
1534 *
1535 * @max_seq is simply an upper bound and does not need to exist. If the caller
1536 * does not require an upper bound, -1 can be used for @max_seq.
1537 */
1538static u64 find_first_fitting_seq(u64 start_seq, u64 max_seq, size_t size,
1539 bool syslog, bool time)
1540{
1541 struct printk_info info;
1542 unsigned int line_count;
1543 size_t len = 0;
1544 u64 seq;
1545
1546 /* Determine the size of the records up to @max_seq. */
1547 prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
1548 if (info.seq >= max_seq)
1549 break;
1550 len += get_record_print_text_size(&info, line_count, syslog, time);
1551 }
1552
1553 /*
1554 * Adjust the upper bound for the next loop to avoid subtracting
1555 * lengths that were never added.
1556 */
1557 if (seq < max_seq)
1558 max_seq = seq;
1559
1560 /*
1561 * Move first record forward until length fits into the buffer. Ignore
1562 * newest messages that were not counted in the above cycle. Messages
1563 * might appear and get lost in the meantime. This is a best effort
1564 * that prevents an infinite loop that could occur with a retry.
1565 */
1566 prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
1567 if (len <= size || info.seq >= max_seq)
1568 break;
1569 len -= get_record_print_text_size(&info, line_count, syslog, time);
1570 }
1571
1572 return seq;
1573}
1574
1575/* The caller is responsible for making sure @size is greater than 0. */
1576static int syslog_print(char __user *buf, int size)
1577{
1578 struct printk_info info;
1579 struct printk_record r;
1580 char *text;
1581 int len = 0;
1582 u64 seq;
1583
1584 text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
1585 if (!text)
1586 return -ENOMEM;
1587
1588 prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
1589
1590 mutex_lock(&syslog_lock);
1591
1592 /*
1593 * Wait for the @syslog_seq record to be available. @syslog_seq may
1594 * change while waiting.
1595 */
1596 do {
1597 seq = syslog_seq;
1598
1599 mutex_unlock(&syslog_lock);
1600 /*
1601 * Guarantee this task is visible on the waitqueue before
1602 * checking the wake condition.
1603 *
1604 * The full memory barrier within set_current_state() of
1605 * prepare_to_wait_event() pairs with the full memory barrier
1606 * within wq_has_sleeper().
1607 *
1608 * This pairs with __wake_up_klogd:A.
1609 */
1610 len = wait_event_interruptible(log_wait,
1611 prb_read_valid(prb, seq, NULL)); /* LMM(syslog_print:A) */
1612 mutex_lock(&syslog_lock);
1613
1614 if (len)
1615 goto out;
1616 } while (syslog_seq != seq);
1617
1618 /*
1619 * Copy records that fit into the buffer. The above cycle makes sure
1620 * that the first record is always available.
1621 */
1622 do {
1623 size_t n;
1624 size_t skip;
1625 int err;
1626
1627 if (!prb_read_valid(prb, syslog_seq, &r))
1628 break;
1629
1630 if (r.info->seq != syslog_seq) {
1631 /* message is gone, move to next valid one */
1632 syslog_seq = r.info->seq;
1633 syslog_partial = 0;
1634 }
1635
1636 /*
1637 * To keep reading/counting partial line consistent,
1638 * use printk_time value as of the beginning of a line.
1639 */
1640 if (!syslog_partial)
1641 syslog_time = printk_time;
1642
1643 skip = syslog_partial;
1644 n = record_print_text(&r, true, syslog_time);
1645 if (n - syslog_partial <= size) {
1646 /* message fits into buffer, move forward */
1647 syslog_seq = r.info->seq + 1;
1648 n -= syslog_partial;
1649 syslog_partial = 0;
1650 } else if (!len){
1651 /* partial read(), remember position */
1652 n = size;
1653 syslog_partial += n;
1654 } else
1655 n = 0;
1656
1657 if (!n)
1658 break;
1659
1660 mutex_unlock(&syslog_lock);
1661 err = copy_to_user(buf, text + skip, n);
1662 mutex_lock(&syslog_lock);
1663
1664 if (err) {
1665 if (!len)
1666 len = -EFAULT;
1667 break;
1668 }
1669
1670 len += n;
1671 size -= n;
1672 buf += n;
1673 } while (size);
1674out:
1675 mutex_unlock(&syslog_lock);
1676 kfree(text);
1677 return len;
1678}
1679
1680static int syslog_print_all(char __user *buf, int size, bool clear)
1681{
1682 struct printk_info info;
1683 struct printk_record r;
1684 char *text;
1685 int len = 0;
1686 u64 seq;
1687 bool time;
1688
1689 text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
1690 if (!text)
1691 return -ENOMEM;
1692
1693 time = printk_time;
1694 /*
1695 * Find first record that fits, including all following records,
1696 * into the user-provided buffer for this dump.
1697 */
1698 seq = find_first_fitting_seq(latched_seq_read_nolock(&clear_seq), -1,
1699 size, true, time);
1700
1701 prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
1702
1703 len = 0;
1704 prb_for_each_record(seq, prb, seq, &r) {
1705 int textlen;
1706
1707 textlen = record_print_text(&r, true, time);
1708
1709 if (len + textlen > size) {
1710 seq--;
1711 break;
1712 }
1713
1714 if (copy_to_user(buf + len, text, textlen))
1715 len = -EFAULT;
1716 else
1717 len += textlen;
1718
1719 if (len < 0)
1720 break;
1721 }
1722
1723 if (clear) {
1724 mutex_lock(&syslog_lock);
1725 latched_seq_write(&clear_seq, seq);
1726 mutex_unlock(&syslog_lock);
1727 }
1728
1729 kfree(text);
1730 return len;
1731}
1732
1733static void syslog_clear(void)
1734{
1735 mutex_lock(&syslog_lock);
1736 latched_seq_write(&clear_seq, prb_next_seq(prb));
1737 mutex_unlock(&syslog_lock);
1738}
1739
1740int do_syslog(int type, char __user *buf, int len, int source)
1741{
1742 struct printk_info info;
1743 bool clear = false;
1744 static int saved_console_loglevel = LOGLEVEL_DEFAULT;
1745 int error;
1746
1747 error = check_syslog_permissions(type, source);
1748 if (error)
1749 return error;
1750
1751 switch (type) {
1752 case SYSLOG_ACTION_CLOSE: /* Close log */
1753 break;
1754 case SYSLOG_ACTION_OPEN: /* Open log */
1755 break;
1756 case SYSLOG_ACTION_READ: /* Read from log */
1757 if (!buf || len < 0)
1758 return -EINVAL;
1759 if (!len)
1760 return 0;
1761 if (!access_ok(buf, len))
1762 return -EFAULT;
1763 error = syslog_print(buf, len);
1764 break;
1765 /* Read/clear last kernel messages */
1766 case SYSLOG_ACTION_READ_CLEAR:
1767 clear = true;
1768 fallthrough;
1769 /* Read last kernel messages */
1770 case SYSLOG_ACTION_READ_ALL:
1771 if (!buf || len < 0)
1772 return -EINVAL;
1773 if (!len)
1774 return 0;
1775 if (!access_ok(buf, len))
1776 return -EFAULT;
1777 error = syslog_print_all(buf, len, clear);
1778 break;
1779 /* Clear ring buffer */
1780 case SYSLOG_ACTION_CLEAR:
1781 syslog_clear();
1782 break;
1783 /* Disable logging to console */
1784 case SYSLOG_ACTION_CONSOLE_OFF:
1785 if (saved_console_loglevel == LOGLEVEL_DEFAULT)
1786 saved_console_loglevel = console_loglevel;
1787 console_loglevel = minimum_console_loglevel;
1788 break;
1789 /* Enable logging to console */
1790 case SYSLOG_ACTION_CONSOLE_ON:
1791 if (saved_console_loglevel != LOGLEVEL_DEFAULT) {
1792 console_loglevel = saved_console_loglevel;
1793 saved_console_loglevel = LOGLEVEL_DEFAULT;
1794 }
1795 break;
1796 /* Set level of messages printed to console */
1797 case SYSLOG_ACTION_CONSOLE_LEVEL:
1798 if (len < 1 || len > 8)
1799 return -EINVAL;
1800 if (len < minimum_console_loglevel)
1801 len = minimum_console_loglevel;
1802 console_loglevel = len;
1803 /* Implicitly re-enable logging to console */
1804 saved_console_loglevel = LOGLEVEL_DEFAULT;
1805 break;
1806 /* Number of chars in the log buffer */
1807 case SYSLOG_ACTION_SIZE_UNREAD:
1808 mutex_lock(&syslog_lock);
1809 if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) {
1810 /* No unread messages. */
1811 mutex_unlock(&syslog_lock);
1812 return 0;
1813 }
1814 if (info.seq != syslog_seq) {
1815 /* messages are gone, move to first one */
1816 syslog_seq = info.seq;
1817 syslog_partial = 0;
1818 }
1819 if (source == SYSLOG_FROM_PROC) {
1820 /*
1821 * Short-cut for poll(/"proc/kmsg") which simply checks
1822 * for pending data, not the size; return the count of
1823 * records, not the length.
1824 */
1825 error = prb_next_seq(prb) - syslog_seq;
1826 } else {
1827 bool time = syslog_partial ? syslog_time : printk_time;
1828 unsigned int line_count;
1829 u64 seq;
1830
1831 prb_for_each_info(syslog_seq, prb, seq, &info,
1832 &line_count) {
1833 error += get_record_print_text_size(&info, line_count,
1834 true, time);
1835 time = printk_time;
1836 }
1837 error -= syslog_partial;
1838 }
1839 mutex_unlock(&syslog_lock);
1840 break;
1841 /* Size of the log buffer */
1842 case SYSLOG_ACTION_SIZE_BUFFER:
1843 error = log_buf_len;
1844 break;
1845 default:
1846 error = -EINVAL;
1847 break;
1848 }
1849
1850 return error;
1851}
1852
1853SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
1854{
1855 return do_syslog(type, buf, len, SYSLOG_FROM_READER);
1856}
1857
1858/*
1859 * Special console_lock variants that help to reduce the risk of soft-lockups.
1860 * They allow to pass console_lock to another printk() call using a busy wait.
1861 */
1862
1863#ifdef CONFIG_LOCKDEP
1864static struct lockdep_map console_owner_dep_map = {
1865 .name = "console_owner"
1866};
1867#endif
1868
1869static DEFINE_RAW_SPINLOCK(console_owner_lock);
1870static struct task_struct *console_owner;
1871static bool console_waiter;
1872
1873/**
1874 * console_lock_spinning_enable - mark beginning of code where another
1875 * thread might safely busy wait
1876 *
1877 * This basically converts console_lock into a spinlock. This marks
1878 * the section where the console_lock owner can not sleep, because
1879 * there may be a waiter spinning (like a spinlock). Also it must be
1880 * ready to hand over the lock at the end of the section.
1881 */
1882static void console_lock_spinning_enable(void)
1883{
1884 raw_spin_lock(&console_owner_lock);
1885 console_owner = current;
1886 raw_spin_unlock(&console_owner_lock);
1887
1888 /* The waiter may spin on us after setting console_owner */
1889 spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
1890}
1891
1892/**
1893 * console_lock_spinning_disable_and_check - mark end of code where another
1894 * thread was able to busy wait and check if there is a waiter
1895 * @cookie: cookie returned from console_srcu_read_lock()
1896 *
1897 * This is called at the end of the section where spinning is allowed.
1898 * It has two functions. First, it is a signal that it is no longer
1899 * safe to start busy waiting for the lock. Second, it checks if
1900 * there is a busy waiter and passes the lock rights to her.
1901 *
1902 * Important: Callers lose both the console_lock and the SRCU read lock if
1903 * there was a busy waiter. They must not touch items synchronized by
1904 * console_lock or SRCU read lock in this case.
1905 *
1906 * Return: 1 if the lock rights were passed, 0 otherwise.
1907 */
1908static int console_lock_spinning_disable_and_check(int cookie)
1909{
1910 int waiter;
1911
1912 raw_spin_lock(&console_owner_lock);
1913 waiter = READ_ONCE(console_waiter);
1914 console_owner = NULL;
1915 raw_spin_unlock(&console_owner_lock);
1916
1917 if (!waiter) {
1918 spin_release(&console_owner_dep_map, _THIS_IP_);
1919 return 0;
1920 }
1921
1922 /* The waiter is now free to continue */
1923 WRITE_ONCE(console_waiter, false);
1924
1925 spin_release(&console_owner_dep_map, _THIS_IP_);
1926
1927 /*
1928 * Preserve lockdep lock ordering. Release the SRCU read lock before
1929 * releasing the console_lock.
1930 */
1931 console_srcu_read_unlock(cookie);
1932
1933 /*
1934 * Hand off console_lock to waiter. The waiter will perform
1935 * the up(). After this, the waiter is the console_lock owner.
1936 */
1937 mutex_release(&console_lock_dep_map, _THIS_IP_);
1938 return 1;
1939}
1940
1941/**
1942 * console_trylock_spinning - try to get console_lock by busy waiting
1943 *
1944 * This allows to busy wait for the console_lock when the current
1945 * owner is running in specially marked sections. It means that
1946 * the current owner is running and cannot reschedule until it
1947 * is ready to lose the lock.
1948 *
1949 * Return: 1 if we got the lock, 0 othrewise
1950 */
1951static int console_trylock_spinning(void)
1952{
1953 struct task_struct *owner = NULL;
1954 bool waiter;
1955 bool spin = false;
1956 unsigned long flags;
1957
1958 if (console_trylock())
1959 return 1;
1960
1961 /*
1962 * It's unsafe to spin once a panic has begun. If we are the
1963 * panic CPU, we may have already halted the owner of the
1964 * console_sem. If we are not the panic CPU, then we should
1965 * avoid taking console_sem, so the panic CPU has a better
1966 * chance of cleanly acquiring it later.
1967 */
1968 if (panic_in_progress())
1969 return 0;
1970
1971 printk_safe_enter_irqsave(flags);
1972
1973 raw_spin_lock(&console_owner_lock);
1974 owner = READ_ONCE(console_owner);
1975 waiter = READ_ONCE(console_waiter);
1976 if (!waiter && owner && owner != current) {
1977 WRITE_ONCE(console_waiter, true);
1978 spin = true;
1979 }
1980 raw_spin_unlock(&console_owner_lock);
1981
1982 /*
1983 * If there is an active printk() writing to the
1984 * consoles, instead of having it write our data too,
1985 * see if we can offload that load from the active
1986 * printer, and do some printing ourselves.
1987 * Go into a spin only if there isn't already a waiter
1988 * spinning, and there is an active printer, and
1989 * that active printer isn't us (recursive printk?).
1990 */
1991 if (!spin) {
1992 printk_safe_exit_irqrestore(flags);
1993 return 0;
1994 }
1995
1996 /* We spin waiting for the owner to release us */
1997 spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
1998 /* Owner will clear console_waiter on hand off */
1999 while (READ_ONCE(console_waiter))
2000 cpu_relax();
2001 spin_release(&console_owner_dep_map, _THIS_IP_);
2002
2003 printk_safe_exit_irqrestore(flags);
2004 /*
2005 * The owner passed the console lock to us.
2006 * Since we did not spin on console lock, annotate
2007 * this as a trylock. Otherwise lockdep will
2008 * complain.
2009 */
2010 mutex_acquire(&console_lock_dep_map, 0, 1, _THIS_IP_);
2011
2012 return 1;
2013}
2014
2015/*
2016 * Call the specified console driver, asking it to write out the specified
2017 * text and length. If @dropped_text is non-NULL and any records have been
2018 * dropped, a dropped message will be written out first.
2019 */
2020static void call_console_driver(struct console *con, const char *text, size_t len,
2021 char *dropped_text)
2022{
2023 size_t dropped_len;
2024
2025 if (con->dropped && dropped_text) {
2026 dropped_len = snprintf(dropped_text, DROPPED_TEXT_MAX,
2027 "** %lu printk messages dropped **\n",
2028 con->dropped);
2029 con->dropped = 0;
2030 con->write(con, dropped_text, dropped_len);
2031 }
2032
2033 con->write(con, text, len);
2034}
2035
2036/*
2037 * Recursion is tracked separately on each CPU. If NMIs are supported, an
2038 * additional NMI context per CPU is also separately tracked. Until per-CPU
2039 * is available, a separate "early tracking" is performed.
2040 */
2041static DEFINE_PER_CPU(u8, printk_count);
2042static u8 printk_count_early;
2043#ifdef CONFIG_HAVE_NMI
2044static DEFINE_PER_CPU(u8, printk_count_nmi);
2045static u8 printk_count_nmi_early;
2046#endif
2047
2048/*
2049 * Recursion is limited to keep the output sane. printk() should not require
2050 * more than 1 level of recursion (allowing, for example, printk() to trigger
2051 * a WARN), but a higher value is used in case some printk-internal errors
2052 * exist, such as the ringbuffer validation checks failing.
2053 */
2054#define PRINTK_MAX_RECURSION 3
2055
2056/*
2057 * Return a pointer to the dedicated counter for the CPU+context of the
2058 * caller.
2059 */
2060static u8 *__printk_recursion_counter(void)
2061{
2062#ifdef CONFIG_HAVE_NMI
2063 if (in_nmi()) {
2064 if (printk_percpu_data_ready())
2065 return this_cpu_ptr(&printk_count_nmi);
2066 return &printk_count_nmi_early;
2067 }
2068#endif
2069 if (printk_percpu_data_ready())
2070 return this_cpu_ptr(&printk_count);
2071 return &printk_count_early;
2072}
2073
2074/*
2075 * Enter recursion tracking. Interrupts are disabled to simplify tracking.
2076 * The caller must check the boolean return value to see if the recursion is
2077 * allowed. On failure, interrupts are not disabled.
2078 *
2079 * @recursion_ptr must be a variable of type (u8 *) and is the same variable
2080 * that is passed to printk_exit_irqrestore().
2081 */
2082#define printk_enter_irqsave(recursion_ptr, flags) \
2083({ \
2084 bool success = true; \
2085 \
2086 typecheck(u8 *, recursion_ptr); \
2087 local_irq_save(flags); \
2088 (recursion_ptr) = __printk_recursion_counter(); \
2089 if (*(recursion_ptr) > PRINTK_MAX_RECURSION) { \
2090 local_irq_restore(flags); \
2091 success = false; \
2092 } else { \
2093 (*(recursion_ptr))++; \
2094 } \
2095 success; \
2096})
2097
2098/* Exit recursion tracking, restoring interrupts. */
2099#define printk_exit_irqrestore(recursion_ptr, flags) \
2100 do { \
2101 typecheck(u8 *, recursion_ptr); \
2102 (*(recursion_ptr))--; \
2103 local_irq_restore(flags); \
2104 } while (0)
2105
2106int printk_delay_msec __read_mostly;
2107
2108static inline void printk_delay(int level)
2109{
2110 boot_delay_msec(level);
2111
2112 if (unlikely(printk_delay_msec)) {
2113 int m = printk_delay_msec;
2114
2115 while (m--) {
2116 mdelay(1);
2117 touch_nmi_watchdog();
2118 }
2119 }
2120}
2121
2122static inline u32 printk_caller_id(void)
2123{
2124 return in_task() ? task_pid_nr(current) :
2125 0x80000000 + smp_processor_id();
2126}
2127
2128/**
2129 * printk_parse_prefix - Parse level and control flags.
2130 *
2131 * @text: The terminated text message.
2132 * @level: A pointer to the current level value, will be updated.
2133 * @flags: A pointer to the current printk_info flags, will be updated.
2134 *
2135 * @level may be NULL if the caller is not interested in the parsed value.
2136 * Otherwise the variable pointed to by @level must be set to
2137 * LOGLEVEL_DEFAULT in order to be updated with the parsed value.
2138 *
2139 * @flags may be NULL if the caller is not interested in the parsed value.
2140 * Otherwise the variable pointed to by @flags will be OR'd with the parsed
2141 * value.
2142 *
2143 * Return: The length of the parsed level and control flags.
2144 */
2145u16 printk_parse_prefix(const char *text, int *level,
2146 enum printk_info_flags *flags)
2147{
2148 u16 prefix_len = 0;
2149 int kern_level;
2150
2151 while (*text) {
2152 kern_level = printk_get_level(text);
2153 if (!kern_level)
2154 break;
2155
2156 switch (kern_level) {
2157 case '0' ... '7':
2158 if (level && *level == LOGLEVEL_DEFAULT)
2159 *level = kern_level - '0';
2160 break;
2161 case 'c': /* KERN_CONT */
2162 if (flags)
2163 *flags |= LOG_CONT;
2164 }
2165
2166 prefix_len += 2;
2167 text += 2;
2168 }
2169
2170 return prefix_len;
2171}
2172
2173__printf(5, 0)
2174static u16 printk_sprint(char *text, u16 size, int facility,
2175 enum printk_info_flags *flags, const char *fmt,
2176 va_list args)
2177{
2178 u16 text_len;
2179
2180 text_len = vscnprintf(text, size, fmt, args);
2181
2182 /* Mark and strip a trailing newline. */
2183 if (text_len && text[text_len - 1] == '\n') {
2184 text_len--;
2185 *flags |= LOG_NEWLINE;
2186 }
2187
2188 /* Strip log level and control flags. */
2189 if (facility == 0) {
2190 u16 prefix_len;
2191
2192 prefix_len = printk_parse_prefix(text, NULL, NULL);
2193 if (prefix_len) {
2194 text_len -= prefix_len;
2195 memmove(text, text + prefix_len, text_len);
2196 }
2197 }
2198
2199 trace_console_rcuidle(text, text_len);
2200
2201 return text_len;
2202}
2203
2204__printf(4, 0)
2205int vprintk_store(int facility, int level,
2206 const struct dev_printk_info *dev_info,
2207 const char *fmt, va_list args)
2208{
2209 struct prb_reserved_entry e;
2210 enum printk_info_flags flags = 0;
2211 struct printk_record r;
2212 unsigned long irqflags;
2213 u16 trunc_msg_len = 0;
2214 char prefix_buf[8];
2215 u8 *recursion_ptr;
2216 u16 reserve_size;
2217 va_list args2;
2218 u32 caller_id;
2219 u16 text_len;
2220 int ret = 0;
2221 u64 ts_nsec;
2222
2223 if (!printk_enter_irqsave(recursion_ptr, irqflags))
2224 return 0;
2225
2226 /*
2227 * Since the duration of printk() can vary depending on the message
2228 * and state of the ringbuffer, grab the timestamp now so that it is
2229 * close to the call of printk(). This provides a more deterministic
2230 * timestamp with respect to the caller.
2231 */
2232 ts_nsec = local_clock();
2233
2234 caller_id = printk_caller_id();
2235
2236 /*
2237 * The sprintf needs to come first since the syslog prefix might be
2238 * passed in as a parameter. An extra byte must be reserved so that
2239 * later the vscnprintf() into the reserved buffer has room for the
2240 * terminating '\0', which is not counted by vsnprintf().
2241 */
2242 va_copy(args2, args);
2243 reserve_size = vsnprintf(&prefix_buf[0], sizeof(prefix_buf), fmt, args2) + 1;
2244 va_end(args2);
2245
2246 if (reserve_size > LOG_LINE_MAX)
2247 reserve_size = LOG_LINE_MAX;
2248
2249 /* Extract log level or control flags. */
2250 if (facility == 0)
2251 printk_parse_prefix(&prefix_buf[0], &level, &flags);
2252
2253 if (level == LOGLEVEL_DEFAULT)
2254 level = default_message_loglevel;
2255
2256 if (dev_info)
2257 flags |= LOG_NEWLINE;
2258
2259 if (flags & LOG_CONT) {
2260 prb_rec_init_wr(&r, reserve_size);
2261 if (prb_reserve_in_last(&e, prb, &r, caller_id, LOG_LINE_MAX)) {
2262 text_len = printk_sprint(&r.text_buf[r.info->text_len], reserve_size,
2263 facility, &flags, fmt, args);
2264 r.info->text_len += text_len;
2265
2266 if (flags & LOG_NEWLINE) {
2267 r.info->flags |= LOG_NEWLINE;
2268 prb_final_commit(&e);
2269 } else {
2270 prb_commit(&e);
2271 }
2272
2273 ret = text_len;
2274 goto out;
2275 }
2276 }
2277
2278 /*
2279 * Explicitly initialize the record before every prb_reserve() call.
2280 * prb_reserve_in_last() and prb_reserve() purposely invalidate the
2281 * structure when they fail.
2282 */
2283 prb_rec_init_wr(&r, reserve_size);
2284 if (!prb_reserve(&e, prb, &r)) {
2285 /* truncate the message if it is too long for empty buffer */
2286 truncate_msg(&reserve_size, &trunc_msg_len);
2287
2288 prb_rec_init_wr(&r, reserve_size + trunc_msg_len);
2289 if (!prb_reserve(&e, prb, &r))
2290 goto out;
2291 }
2292
2293 /* fill message */
2294 text_len = printk_sprint(&r.text_buf[0], reserve_size, facility, &flags, fmt, args);
2295 if (trunc_msg_len)
2296 memcpy(&r.text_buf[text_len], trunc_msg, trunc_msg_len);
2297 r.info->text_len = text_len + trunc_msg_len;
2298 r.info->facility = facility;
2299 r.info->level = level & 7;
2300 r.info->flags = flags & 0x1f;
2301 r.info->ts_nsec = ts_nsec;
2302 r.info->caller_id = caller_id;
2303 if (dev_info)
2304 memcpy(&r.info->dev_info, dev_info, sizeof(r.info->dev_info));
2305
2306 /* A message without a trailing newline can be continued. */
2307 if (!(flags & LOG_NEWLINE))
2308 prb_commit(&e);
2309 else
2310 prb_final_commit(&e);
2311
2312 ret = text_len + trunc_msg_len;
2313out:
2314 printk_exit_irqrestore(recursion_ptr, irqflags);
2315 return ret;
2316}
2317
2318asmlinkage int vprintk_emit(int facility, int level,
2319 const struct dev_printk_info *dev_info,
2320 const char *fmt, va_list args)
2321{
2322 int printed_len;
2323 bool in_sched = false;
2324
2325 /* Suppress unimportant messages after panic happens */
2326 if (unlikely(suppress_printk))
2327 return 0;
2328
2329 if (unlikely(suppress_panic_printk) &&
2330 atomic_read(&panic_cpu) != raw_smp_processor_id())
2331 return 0;
2332
2333 if (level == LOGLEVEL_SCHED) {
2334 level = LOGLEVEL_DEFAULT;
2335 in_sched = true;
2336 }
2337
2338 printk_delay(level);
2339
2340 printed_len = vprintk_store(facility, level, dev_info, fmt, args);
2341
2342 /* If called from the scheduler, we can not call up(). */
2343 if (!in_sched) {
2344 /*
2345 * The caller may be holding system-critical or
2346 * timing-sensitive locks. Disable preemption during
2347 * printing of all remaining records to all consoles so that
2348 * this context can return as soon as possible. Hopefully
2349 * another printk() caller will take over the printing.
2350 */
2351 preempt_disable();
2352 /*
2353 * Try to acquire and then immediately release the console
2354 * semaphore. The release will print out buffers. With the
2355 * spinning variant, this context tries to take over the
2356 * printing from another printing context.
2357 */
2358 if (console_trylock_spinning())
2359 console_unlock();
2360 preempt_enable();
2361 }
2362
2363 wake_up_klogd();
2364 return printed_len;
2365}
2366EXPORT_SYMBOL(vprintk_emit);
2367
2368int vprintk_default(const char *fmt, va_list args)
2369{
2370 return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, fmt, args);
2371}
2372EXPORT_SYMBOL_GPL(vprintk_default);
2373
2374asmlinkage __visible int _printk(const char *fmt, ...)
2375{
2376 va_list args;
2377 int r;
2378
2379 va_start(args, fmt);
2380 r = vprintk(fmt, args);
2381 va_end(args);
2382
2383 return r;
2384}
2385EXPORT_SYMBOL(_printk);
2386
2387static bool pr_flush(int timeout_ms, bool reset_on_progress);
2388static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress);
2389
2390#else /* CONFIG_PRINTK */
2391
2392#define CONSOLE_LOG_MAX 0
2393#define DROPPED_TEXT_MAX 0
2394#define printk_time false
2395
2396#define prb_read_valid(rb, seq, r) false
2397#define prb_first_valid_seq(rb) 0
2398#define prb_next_seq(rb) 0
2399
2400static u64 syslog_seq;
2401
2402static size_t record_print_text(const struct printk_record *r,
2403 bool syslog, bool time)
2404{
2405 return 0;
2406}
2407static ssize_t info_print_ext_header(char *buf, size_t size,
2408 struct printk_info *info)
2409{
2410 return 0;
2411}
2412static ssize_t msg_print_ext_body(char *buf, size_t size,
2413 char *text, size_t text_len,
2414 struct dev_printk_info *dev_info) { return 0; }
2415static void console_lock_spinning_enable(void) { }
2416static int console_lock_spinning_disable_and_check(int cookie) { return 0; }
2417static void call_console_driver(struct console *con, const char *text, size_t len,
2418 char *dropped_text)
2419{
2420}
2421static bool suppress_message_printing(int level) { return false; }
2422static bool pr_flush(int timeout_ms, bool reset_on_progress) { return true; }
2423static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { return true; }
2424
2425#endif /* CONFIG_PRINTK */
2426
2427#ifdef CONFIG_EARLY_PRINTK
2428struct console *early_console;
2429
2430asmlinkage __visible void early_printk(const char *fmt, ...)
2431{
2432 va_list ap;
2433 char buf[512];
2434 int n;
2435
2436 if (!early_console)
2437 return;
2438
2439 va_start(ap, fmt);
2440 n = vscnprintf(buf, sizeof(buf), fmt, ap);
2441 va_end(ap);
2442
2443 early_console->write(early_console, buf, n);
2444}
2445#endif
2446
2447static void set_user_specified(struct console_cmdline *c, bool user_specified)
2448{
2449 if (!user_specified)
2450 return;
2451
2452 /*
2453 * @c console was defined by the user on the command line.
2454 * Do not clear when added twice also by SPCR or the device tree.
2455 */
2456 c->user_specified = true;
2457 /* At least one console defined by the user on the command line. */
2458 console_set_on_cmdline = 1;
2459}
2460
2461static int __add_preferred_console(char *name, int idx, char *options,
2462 char *brl_options, bool user_specified)
2463{
2464 struct console_cmdline *c;
2465 int i;
2466
2467 /*
2468 * See if this tty is not yet registered, and
2469 * if we have a slot free.
2470 */
2471 for (i = 0, c = console_cmdline;
2472 i < MAX_CMDLINECONSOLES && c->name[0];
2473 i++, c++) {
2474 if (strcmp(c->name, name) == 0 && c->index == idx) {
2475 if (!brl_options)
2476 preferred_console = i;
2477 set_user_specified(c, user_specified);
2478 return 0;
2479 }
2480 }
2481 if (i == MAX_CMDLINECONSOLES)
2482 return -E2BIG;
2483 if (!brl_options)
2484 preferred_console = i;
2485 strscpy(c->name, name, sizeof(c->name));
2486 c->options = options;
2487 set_user_specified(c, user_specified);
2488 braille_set_options(c, brl_options);
2489
2490 c->index = idx;
2491 return 0;
2492}
2493
2494static int __init console_msg_format_setup(char *str)
2495{
2496 if (!strcmp(str, "syslog"))
2497 console_msg_format = MSG_FORMAT_SYSLOG;
2498 if (!strcmp(str, "default"))
2499 console_msg_format = MSG_FORMAT_DEFAULT;
2500 return 1;
2501}
2502__setup("console_msg_format=", console_msg_format_setup);
2503
2504/*
2505 * Set up a console. Called via do_early_param() in init/main.c
2506 * for each "console=" parameter in the boot command line.
2507 */
2508static int __init console_setup(char *str)
2509{
2510 char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for "ttyS" */
2511 char *s, *options, *brl_options = NULL;
2512 int idx;
2513
2514 /*
2515 * console="" or console=null have been suggested as a way to
2516 * disable console output. Use ttynull that has been created
2517 * for exactly this purpose.
2518 */
2519 if (str[0] == 0 || strcmp(str, "null") == 0) {
2520 __add_preferred_console("ttynull", 0, NULL, NULL, true);
2521 return 1;
2522 }
2523
2524 if (_braille_console_setup(&str, &brl_options))
2525 return 1;
2526
2527 /*
2528 * Decode str into name, index, options.
2529 */
2530 if (str[0] >= '0' && str[0] <= '9') {
2531 strcpy(buf, "ttyS");
2532 strncpy(buf + 4, str, sizeof(buf) - 5);
2533 } else {
2534 strncpy(buf, str, sizeof(buf) - 1);
2535 }
2536 buf[sizeof(buf) - 1] = 0;
2537 options = strchr(str, ',');
2538 if (options)
2539 *(options++) = 0;
2540#ifdef __sparc__
2541 if (!strcmp(str, "ttya"))
2542 strcpy(buf, "ttyS0");
2543 if (!strcmp(str, "ttyb"))
2544 strcpy(buf, "ttyS1");
2545#endif
2546 for (s = buf; *s; s++)
2547 if (isdigit(*s) || *s == ',')
2548 break;
2549 idx = simple_strtoul(s, NULL, 10);
2550 *s = 0;
2551
2552 __add_preferred_console(buf, idx, options, brl_options, true);
2553 return 1;
2554}
2555__setup("console=", console_setup);
2556
2557/**
2558 * add_preferred_console - add a device to the list of preferred consoles.
2559 * @name: device name
2560 * @idx: device index
2561 * @options: options for this console
2562 *
2563 * The last preferred console added will be used for kernel messages
2564 * and stdin/out/err for init. Normally this is used by console_setup
2565 * above to handle user-supplied console arguments; however it can also
2566 * be used by arch-specific code either to override the user or more
2567 * commonly to provide a default console (ie from PROM variables) when
2568 * the user has not supplied one.
2569 */
2570int add_preferred_console(char *name, int idx, char *options)
2571{
2572 return __add_preferred_console(name, idx, options, NULL, false);
2573}
2574
2575bool console_suspend_enabled = true;
2576EXPORT_SYMBOL(console_suspend_enabled);
2577
2578static int __init console_suspend_disable(char *str)
2579{
2580 console_suspend_enabled = false;
2581 return 1;
2582}
2583__setup("no_console_suspend", console_suspend_disable);
2584module_param_named(console_suspend, console_suspend_enabled,
2585 bool, S_IRUGO | S_IWUSR);
2586MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
2587 " and hibernate operations");
2588
2589static bool printk_console_no_auto_verbose;
2590
2591void console_verbose(void)
2592{
2593 if (console_loglevel && !printk_console_no_auto_verbose)
2594 console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
2595}
2596EXPORT_SYMBOL_GPL(console_verbose);
2597
2598module_param_named(console_no_auto_verbose, printk_console_no_auto_verbose, bool, 0644);
2599MODULE_PARM_DESC(console_no_auto_verbose, "Disable console loglevel raise to highest on oops/panic/etc");
2600
2601/**
2602 * suspend_console - suspend the console subsystem
2603 *
2604 * This disables printk() while we go into suspend states
2605 */
2606void suspend_console(void)
2607{
2608 if (!console_suspend_enabled)
2609 return;
2610 pr_info("Suspending console(s) (use no_console_suspend to debug)\n");
2611 pr_flush(1000, true);
2612 console_lock();
2613 console_suspended = 1;
2614 up_console_sem();
2615}
2616
2617void resume_console(void)
2618{
2619 if (!console_suspend_enabled)
2620 return;
2621 down_console_sem();
2622 console_suspended = 0;
2623 console_unlock();
2624 pr_flush(1000, true);
2625}
2626
2627/**
2628 * console_cpu_notify - print deferred console messages after CPU hotplug
2629 * @cpu: unused
2630 *
2631 * If printk() is called from a CPU that is not online yet, the messages
2632 * will be printed on the console only if there are CON_ANYTIME consoles.
2633 * This function is called when a new CPU comes online (or fails to come
2634 * up) or goes offline.
2635 */
2636static int console_cpu_notify(unsigned int cpu)
2637{
2638 if (!cpuhp_tasks_frozen) {
2639 /* If trylock fails, someone else is doing the printing */
2640 if (console_trylock())
2641 console_unlock();
2642 }
2643 return 0;
2644}
2645
2646/**
2647 * console_lock - block the console subsystem from printing
2648 *
2649 * Acquires a lock which guarantees that no consoles will
2650 * be in or enter their write() callback.
2651 *
2652 * Can sleep, returns nothing.
2653 */
2654void console_lock(void)
2655{
2656 might_sleep();
2657
2658 down_console_sem();
2659 if (console_suspended)
2660 return;
2661 console_locked = 1;
2662 console_may_schedule = 1;
2663}
2664EXPORT_SYMBOL(console_lock);
2665
2666/**
2667 * console_trylock - try to block the console subsystem from printing
2668 *
2669 * Try to acquire a lock which guarantees that no consoles will
2670 * be in or enter their write() callback.
2671 *
2672 * returns 1 on success, and 0 on failure to acquire the lock.
2673 */
2674int console_trylock(void)
2675{
2676 if (down_trylock_console_sem())
2677 return 0;
2678 if (console_suspended) {
2679 up_console_sem();
2680 return 0;
2681 }
2682 console_locked = 1;
2683 console_may_schedule = 0;
2684 return 1;
2685}
2686EXPORT_SYMBOL(console_trylock);
2687
2688int is_console_locked(void)
2689{
2690 return console_locked;
2691}
2692EXPORT_SYMBOL(is_console_locked);
2693
2694/*
2695 * Return true when this CPU should unlock console_sem without pushing all
2696 * messages to the console. This reduces the chance that the console is
2697 * locked when the panic CPU tries to use it.
2698 */
2699static bool abandon_console_lock_in_panic(void)
2700{
2701 if (!panic_in_progress())
2702 return false;
2703
2704 /*
2705 * We can use raw_smp_processor_id() here because it is impossible for
2706 * the task to be migrated to the panic_cpu, or away from it. If
2707 * panic_cpu has already been set, and we're not currently executing on
2708 * that CPU, then we never will be.
2709 */
2710 return atomic_read(&panic_cpu) != raw_smp_processor_id();
2711}
2712
2713/*
2714 * Check if the given console is currently capable and allowed to print
2715 * records.
2716 *
2717 * Requires the console_srcu_read_lock.
2718 */
2719static inline bool console_is_usable(struct console *con)
2720{
2721 short flags = console_srcu_read_flags(con);
2722
2723 if (!(flags & CON_ENABLED))
2724 return false;
2725
2726 if (!con->write)
2727 return false;
2728
2729 /*
2730 * Console drivers may assume that per-cpu resources have been
2731 * allocated. So unless they're explicitly marked as being able to
2732 * cope (CON_ANYTIME) don't call them until this CPU is officially up.
2733 */
2734 if (!cpu_online(raw_smp_processor_id()) && !(flags & CON_ANYTIME))
2735 return false;
2736
2737 return true;
2738}
2739
2740static void __console_unlock(void)
2741{
2742 console_locked = 0;
2743 up_console_sem();
2744}
2745
2746/*
2747 * Print one record for the given console. The record printed is whatever
2748 * record is the next available record for the given console.
2749 *
2750 * @text is a buffer of size CONSOLE_LOG_MAX.
2751 *
2752 * If extended messages should be printed, @ext_text is a buffer of size
2753 * CONSOLE_EXT_LOG_MAX. Otherwise @ext_text must be NULL.
2754 *
2755 * If dropped messages should be printed, @dropped_text is a buffer of size
2756 * DROPPED_TEXT_MAX. Otherwise @dropped_text must be NULL.
2757 *
2758 * @handover will be set to true if a printk waiter has taken over the
2759 * console_lock, in which case the caller is no longer holding both the
2760 * console_lock and the SRCU read lock. Otherwise it is set to false.
2761 *
2762 * @cookie is the cookie from the SRCU read lock.
2763 *
2764 * Returns false if the given console has no next record to print, otherwise
2765 * true.
2766 *
2767 * Requires the console_lock and the SRCU read lock.
2768 */
2769static bool console_emit_next_record(struct console *con, char *text, char *ext_text,
2770 char *dropped_text, bool *handover, int cookie)
2771{
2772 static int panic_console_dropped;
2773 struct printk_info info;
2774 struct printk_record r;
2775 unsigned long flags;
2776 char *write_text;
2777 size_t len;
2778
2779 prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
2780
2781 *handover = false;
2782
2783 if (!prb_read_valid(prb, con->seq, &r))
2784 return false;
2785
2786 if (con->seq != r.info->seq) {
2787 con->dropped += r.info->seq - con->seq;
2788 con->seq = r.info->seq;
2789 if (panic_in_progress() && panic_console_dropped++ > 10) {
2790 suppress_panic_printk = 1;
2791 pr_warn_once("Too many dropped messages. Suppress messages on non-panic CPUs to prevent livelock.\n");
2792 }
2793 }
2794
2795 /* Skip record that has level above the console loglevel. */
2796 if (suppress_message_printing(r.info->level)) {
2797 con->seq++;
2798 goto skip;
2799 }
2800
2801 if (ext_text) {
2802 write_text = ext_text;
2803 len = info_print_ext_header(ext_text, CONSOLE_EXT_LOG_MAX, r.info);
2804 len += msg_print_ext_body(ext_text + len, CONSOLE_EXT_LOG_MAX - len,
2805 &r.text_buf[0], r.info->text_len, &r.info->dev_info);
2806 } else {
2807 write_text = text;
2808 len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time);
2809 }
2810
2811 /*
2812 * While actively printing out messages, if another printk()
2813 * were to occur on another CPU, it may wait for this one to
2814 * finish. This task can not be preempted if there is a
2815 * waiter waiting to take over.
2816 *
2817 * Interrupts are disabled because the hand over to a waiter
2818 * must not be interrupted until the hand over is completed
2819 * (@console_waiter is cleared).
2820 */
2821 printk_safe_enter_irqsave(flags);
2822 console_lock_spinning_enable();
2823
2824 stop_critical_timings(); /* don't trace print latency */
2825 call_console_driver(con, write_text, len, dropped_text);
2826 start_critical_timings();
2827
2828 con->seq++;
2829
2830 *handover = console_lock_spinning_disable_and_check(cookie);
2831 printk_safe_exit_irqrestore(flags);
2832skip:
2833 return true;
2834}
2835
2836/*
2837 * Print out all remaining records to all consoles.
2838 *
2839 * @do_cond_resched is set by the caller. It can be true only in schedulable
2840 * context.
2841 *
2842 * @next_seq is set to the sequence number after the last available record.
2843 * The value is valid only when this function returns true. It means that all
2844 * usable consoles are completely flushed.
2845 *
2846 * @handover will be set to true if a printk waiter has taken over the
2847 * console_lock, in which case the caller is no longer holding the
2848 * console_lock. Otherwise it is set to false.
2849 *
2850 * Returns true when there was at least one usable console and all messages
2851 * were flushed to all usable consoles. A returned false informs the caller
2852 * that everything was not flushed (either there were no usable consoles or
2853 * another context has taken over printing or it is a panic situation and this
2854 * is not the panic CPU). Regardless the reason, the caller should assume it
2855 * is not useful to immediately try again.
2856 *
2857 * Requires the console_lock.
2858 */
2859static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handover)
2860{
2861 static char dropped_text[DROPPED_TEXT_MAX];
2862 static char ext_text[CONSOLE_EXT_LOG_MAX];
2863 static char text[CONSOLE_LOG_MAX];
2864 bool any_usable = false;
2865 struct console *con;
2866 bool any_progress;
2867 int cookie;
2868
2869 *next_seq = 0;
2870 *handover = false;
2871
2872 do {
2873 any_progress = false;
2874
2875 cookie = console_srcu_read_lock();
2876 for_each_console_srcu(con) {
2877 bool progress;
2878
2879 if (!console_is_usable(con))
2880 continue;
2881 any_usable = true;
2882
2883 if (console_srcu_read_flags(con) & CON_EXTENDED) {
2884 /* Extended consoles do not print "dropped messages". */
2885 progress = console_emit_next_record(con, &text[0],
2886 &ext_text[0], NULL,
2887 handover, cookie);
2888 } else {
2889 progress = console_emit_next_record(con, &text[0],
2890 NULL, &dropped_text[0],
2891 handover, cookie);
2892 }
2893
2894 /*
2895 * If a handover has occurred, the SRCU read lock
2896 * is already released.
2897 */
2898 if (*handover)
2899 return false;
2900
2901 /* Track the next of the highest seq flushed. */
2902 if (con->seq > *next_seq)
2903 *next_seq = con->seq;
2904
2905 if (!progress)
2906 continue;
2907 any_progress = true;
2908
2909 /* Allow panic_cpu to take over the consoles safely. */
2910 if (abandon_console_lock_in_panic())
2911 goto abandon;
2912
2913 if (do_cond_resched)
2914 cond_resched();
2915 }
2916 console_srcu_read_unlock(cookie);
2917 } while (any_progress);
2918
2919 return any_usable;
2920
2921abandon:
2922 console_srcu_read_unlock(cookie);
2923 return false;
2924}
2925
2926/**
2927 * console_unlock - unblock the console subsystem from printing
2928 *
2929 * Releases the console_lock which the caller holds to block printing of
2930 * the console subsystem.
2931 *
2932 * While the console_lock was held, console output may have been buffered
2933 * by printk(). If this is the case, console_unlock(); emits
2934 * the output prior to releasing the lock.
2935 *
2936 * console_unlock(); may be called from any context.
2937 */
2938void console_unlock(void)
2939{
2940 bool do_cond_resched;
2941 bool handover;
2942 bool flushed;
2943 u64 next_seq;
2944
2945 if (console_suspended) {
2946 up_console_sem();
2947 return;
2948 }
2949
2950 /*
2951 * Console drivers are called with interrupts disabled, so
2952 * @console_may_schedule should be cleared before; however, we may
2953 * end up dumping a lot of lines, for example, if called from
2954 * console registration path, and should invoke cond_resched()
2955 * between lines if allowable. Not doing so can cause a very long
2956 * scheduling stall on a slow console leading to RCU stall and
2957 * softlockup warnings which exacerbate the issue with more
2958 * messages practically incapacitating the system. Therefore, create
2959 * a local to use for the printing loop.
2960 */
2961 do_cond_resched = console_may_schedule;
2962
2963 do {
2964 console_may_schedule = 0;
2965
2966 flushed = console_flush_all(do_cond_resched, &next_seq, &handover);
2967 if (!handover)
2968 __console_unlock();
2969
2970 /*
2971 * Abort if there was a failure to flush all messages to all
2972 * usable consoles. Either it is not possible to flush (in
2973 * which case it would be an infinite loop of retrying) or
2974 * another context has taken over printing.
2975 */
2976 if (!flushed)
2977 break;
2978
2979 /*
2980 * Some context may have added new records after
2981 * console_flush_all() but before unlocking the console.
2982 * Re-check if there is a new record to flush. If the trylock
2983 * fails, another context is already handling the printing.
2984 */
2985 } while (prb_read_valid(prb, next_seq, NULL) && console_trylock());
2986}
2987EXPORT_SYMBOL(console_unlock);
2988
2989/**
2990 * console_conditional_schedule - yield the CPU if required
2991 *
2992 * If the console code is currently allowed to sleep, and
2993 * if this CPU should yield the CPU to another task, do
2994 * so here.
2995 *
2996 * Must be called within console_lock();.
2997 */
2998void __sched console_conditional_schedule(void)
2999{
3000 if (console_may_schedule)
3001 cond_resched();
3002}
3003EXPORT_SYMBOL(console_conditional_schedule);
3004
3005void console_unblank(void)
3006{
3007 struct console *c;
3008 int cookie;
3009
3010 /*
3011 * Stop console printing because the unblank() callback may
3012 * assume the console is not within its write() callback.
3013 *
3014 * If @oops_in_progress is set, this may be an atomic context.
3015 * In that case, attempt a trylock as best-effort.
3016 */
3017 if (oops_in_progress) {
3018 if (down_trylock_console_sem() != 0)
3019 return;
3020 } else
3021 console_lock();
3022
3023 console_locked = 1;
3024 console_may_schedule = 0;
3025
3026 cookie = console_srcu_read_lock();
3027 for_each_console_srcu(c) {
3028 if ((console_srcu_read_flags(c) & CON_ENABLED) && c->unblank)
3029 c->unblank();
3030 }
3031 console_srcu_read_unlock(cookie);
3032
3033 console_unlock();
3034
3035 if (!oops_in_progress)
3036 pr_flush(1000, true);
3037}
3038
3039/**
3040 * console_flush_on_panic - flush console content on panic
3041 * @mode: flush all messages in buffer or just the pending ones
3042 *
3043 * Immediately output all pending messages no matter what.
3044 */
3045void console_flush_on_panic(enum con_flush_mode mode)
3046{
3047 /*
3048 * If someone else is holding the console lock, trylock will fail
3049 * and may_schedule may be set. Ignore and proceed to unlock so
3050 * that messages are flushed out. As this can be called from any
3051 * context and we don't want to get preempted while flushing,
3052 * ensure may_schedule is cleared.
3053 */
3054 console_trylock();
3055 console_may_schedule = 0;
3056
3057 if (mode == CONSOLE_REPLAY_ALL) {
3058 struct console *c;
3059 int cookie;
3060 u64 seq;
3061
3062 seq = prb_first_valid_seq(prb);
3063
3064 cookie = console_srcu_read_lock();
3065 for_each_console_srcu(c) {
3066 /*
3067 * If the above console_trylock() failed, this is an
3068 * unsynchronized assignment. But in that case, the
3069 * kernel is in "hope and pray" mode anyway.
3070 */
3071 c->seq = seq;
3072 }
3073 console_srcu_read_unlock(cookie);
3074 }
3075 console_unlock();
3076}
3077
3078/*
3079 * Return the console tty driver structure and its associated index
3080 */
3081struct tty_driver *console_device(int *index)
3082{
3083 struct console *c;
3084 struct tty_driver *driver = NULL;
3085 int cookie;
3086
3087 /*
3088 * Take console_lock to serialize device() callback with
3089 * other console operations. For example, fg_console is
3090 * modified under console_lock when switching vt.
3091 */
3092 console_lock();
3093
3094 cookie = console_srcu_read_lock();
3095 for_each_console_srcu(c) {
3096 if (!c->device)
3097 continue;
3098 driver = c->device(c, index);
3099 if (driver)
3100 break;
3101 }
3102 console_srcu_read_unlock(cookie);
3103
3104 console_unlock();
3105 return driver;
3106}
3107
3108/*
3109 * Prevent further output on the passed console device so that (for example)
3110 * serial drivers can disable console output before suspending a port, and can
3111 * re-enable output afterwards.
3112 */
3113void console_stop(struct console *console)
3114{
3115 __pr_flush(console, 1000, true);
3116 console_list_lock();
3117 console_srcu_write_flags(console, console->flags & ~CON_ENABLED);
3118 console_list_unlock();
3119
3120 /*
3121 * Ensure that all SRCU list walks have completed. All contexts must
3122 * be able to see that this console is disabled so that (for example)
3123 * the caller can suspend the port without risk of another context
3124 * using the port.
3125 */
3126 synchronize_srcu(&console_srcu);
3127}
3128EXPORT_SYMBOL(console_stop);
3129
3130void console_start(struct console *console)
3131{
3132 console_list_lock();
3133 console_srcu_write_flags(console, console->flags | CON_ENABLED);
3134 console_list_unlock();
3135 __pr_flush(console, 1000, true);
3136}
3137EXPORT_SYMBOL(console_start);
3138
3139static int __read_mostly keep_bootcon;
3140
3141static int __init keep_bootcon_setup(char *str)
3142{
3143 keep_bootcon = 1;
3144 pr_info("debug: skip boot console de-registration.\n");
3145
3146 return 0;
3147}
3148
3149early_param("keep_bootcon", keep_bootcon_setup);
3150
3151/*
3152 * This is called by register_console() to try to match
3153 * the newly registered console with any of the ones selected
3154 * by either the command line or add_preferred_console() and
3155 * setup/enable it.
3156 *
3157 * Care need to be taken with consoles that are statically
3158 * enabled such as netconsole
3159 */
3160static int try_enable_preferred_console(struct console *newcon,
3161 bool user_specified)
3162{
3163 struct console_cmdline *c;
3164 int i, err;
3165
3166 for (i = 0, c = console_cmdline;
3167 i < MAX_CMDLINECONSOLES && c->name[0];
3168 i++, c++) {
3169 if (c->user_specified != user_specified)
3170 continue;
3171 if (!newcon->match ||
3172 newcon->match(newcon, c->name, c->index, c->options) != 0) {
3173 /* default matching */
3174 BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));
3175 if (strcmp(c->name, newcon->name) != 0)
3176 continue;
3177 if (newcon->index >= 0 &&
3178 newcon->index != c->index)
3179 continue;
3180 if (newcon->index < 0)
3181 newcon->index = c->index;
3182
3183 if (_braille_register_console(newcon, c))
3184 return 0;
3185
3186 if (newcon->setup &&
3187 (err = newcon->setup(newcon, c->options)) != 0)
3188 return err;
3189 }
3190 newcon->flags |= CON_ENABLED;
3191 if (i == preferred_console)
3192 newcon->flags |= CON_CONSDEV;
3193 return 0;
3194 }
3195
3196 /*
3197 * Some consoles, such as pstore and netconsole, can be enabled even
3198 * without matching. Accept the pre-enabled consoles only when match()
3199 * and setup() had a chance to be called.
3200 */
3201 if (newcon->flags & CON_ENABLED && c->user_specified == user_specified)
3202 return 0;
3203
3204 return -ENOENT;
3205}
3206
3207/* Try to enable the console unconditionally */
3208static void try_enable_default_console(struct console *newcon)
3209{
3210 if (newcon->index < 0)
3211 newcon->index = 0;
3212
3213 if (newcon->setup && newcon->setup(newcon, NULL) != 0)
3214 return;
3215
3216 newcon->flags |= CON_ENABLED;
3217
3218 if (newcon->device)
3219 newcon->flags |= CON_CONSDEV;
3220}
3221
3222#define con_printk(lvl, con, fmt, ...) \
3223 printk(lvl pr_fmt("%sconsole [%s%d] " fmt), \
3224 (con->flags & CON_BOOT) ? "boot" : "", \
3225 con->name, con->index, ##__VA_ARGS__)
3226
3227static void console_init_seq(struct console *newcon, bool bootcon_registered)
3228{
3229 struct console *con;
3230 bool handover;
3231
3232 if (newcon->flags & (CON_PRINTBUFFER | CON_BOOT)) {
3233 /* Get a consistent copy of @syslog_seq. */
3234 mutex_lock(&syslog_lock);
3235 newcon->seq = syslog_seq;
3236 mutex_unlock(&syslog_lock);
3237 } else {
3238 /* Begin with next message added to ringbuffer. */
3239 newcon->seq = prb_next_seq(prb);
3240
3241 /*
3242 * If any enabled boot consoles are due to be unregistered
3243 * shortly, some may not be caught up and may be the same
3244 * device as @newcon. Since it is not known which boot console
3245 * is the same device, flush all consoles and, if necessary,
3246 * start with the message of the enabled boot console that is
3247 * the furthest behind.
3248 */
3249 if (bootcon_registered && !keep_bootcon) {
3250 /*
3251 * Hold the console_lock to stop console printing and
3252 * guarantee safe access to console->seq.
3253 */
3254 console_lock();
3255
3256 /*
3257 * Flush all consoles and set the console to start at
3258 * the next unprinted sequence number.
3259 */
3260 if (!console_flush_all(true, &newcon->seq, &handover)) {
3261 /*
3262 * Flushing failed. Just choose the lowest
3263 * sequence of the enabled boot consoles.
3264 */
3265
3266 /*
3267 * If there was a handover, this context no
3268 * longer holds the console_lock.
3269 */
3270 if (handover)
3271 console_lock();
3272
3273 newcon->seq = prb_next_seq(prb);
3274 for_each_console(con) {
3275 if ((con->flags & CON_BOOT) &&
3276 (con->flags & CON_ENABLED) &&
3277 con->seq < newcon->seq) {
3278 newcon->seq = con->seq;
3279 }
3280 }
3281 }
3282
3283 console_unlock();
3284 }
3285 }
3286}
3287
3288#define console_first() \
3289 hlist_entry(console_list.first, struct console, node)
3290
3291static int unregister_console_locked(struct console *console);
3292
3293/*
3294 * The console driver calls this routine during kernel initialization
3295 * to register the console printing procedure with printk() and to
3296 * print any messages that were printed by the kernel before the
3297 * console driver was initialized.
3298 *
3299 * This can happen pretty early during the boot process (because of
3300 * early_printk) - sometimes before setup_arch() completes - be careful
3301 * of what kernel features are used - they may not be initialised yet.
3302 *
3303 * There are two types of consoles - bootconsoles (early_printk) and
3304 * "real" consoles (everything which is not a bootconsole) which are
3305 * handled differently.
3306 * - Any number of bootconsoles can be registered at any time.
3307 * - As soon as a "real" console is registered, all bootconsoles
3308 * will be unregistered automatically.
3309 * - Once a "real" console is registered, any attempt to register a
3310 * bootconsoles will be rejected
3311 */
3312void register_console(struct console *newcon)
3313{
3314 struct console *con;
3315 bool bootcon_registered = false;
3316 bool realcon_registered = false;
3317 int err;
3318
3319 console_list_lock();
3320
3321 for_each_console(con) {
3322 if (WARN(con == newcon, "console '%s%d' already registered\n",
3323 con->name, con->index)) {
3324 goto unlock;
3325 }
3326
3327 if (con->flags & CON_BOOT)
3328 bootcon_registered = true;
3329 else
3330 realcon_registered = true;
3331 }
3332
3333 /* Do not register boot consoles when there already is a real one. */
3334 if ((newcon->flags & CON_BOOT) && realcon_registered) {
3335 pr_info("Too late to register bootconsole %s%d\n",
3336 newcon->name, newcon->index);
3337 goto unlock;
3338 }
3339
3340 /*
3341 * See if we want to enable this console driver by default.
3342 *
3343 * Nope when a console is preferred by the command line, device
3344 * tree, or SPCR.
3345 *
3346 * The first real console with tty binding (driver) wins. More
3347 * consoles might get enabled before the right one is found.
3348 *
3349 * Note that a console with tty binding will have CON_CONSDEV
3350 * flag set and will be first in the list.
3351 */
3352 if (preferred_console < 0) {
3353 if (hlist_empty(&console_list) || !console_first()->device ||
3354 console_first()->flags & CON_BOOT) {
3355 try_enable_default_console(newcon);
3356 }
3357 }
3358
3359 /* See if this console matches one we selected on the command line */
3360 err = try_enable_preferred_console(newcon, true);
3361
3362 /* If not, try to match against the platform default(s) */
3363 if (err == -ENOENT)
3364 err = try_enable_preferred_console(newcon, false);
3365
3366 /* printk() messages are not printed to the Braille console. */
3367 if (err || newcon->flags & CON_BRL)
3368 goto unlock;
3369
3370 /*
3371 * If we have a bootconsole, and are switching to a real console,
3372 * don't print everything out again, since when the boot console, and
3373 * the real console are the same physical device, it's annoying to
3374 * see the beginning boot messages twice
3375 */
3376 if (bootcon_registered &&
3377 ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
3378 newcon->flags &= ~CON_PRINTBUFFER;
3379 }
3380
3381 newcon->dropped = 0;
3382 console_init_seq(newcon, bootcon_registered);
3383
3384 /*
3385 * Put this console in the list - keep the
3386 * preferred driver at the head of the list.
3387 */
3388 if (hlist_empty(&console_list)) {
3389 /* Ensure CON_CONSDEV is always set for the head. */
3390 newcon->flags |= CON_CONSDEV;
3391 hlist_add_head_rcu(&newcon->node, &console_list);
3392
3393 } else if (newcon->flags & CON_CONSDEV) {
3394 /* Only the new head can have CON_CONSDEV set. */
3395 console_srcu_write_flags(console_first(), console_first()->flags & ~CON_CONSDEV);
3396 hlist_add_head_rcu(&newcon->node, &console_list);
3397
3398 } else {
3399 hlist_add_behind_rcu(&newcon->node, console_list.first);
3400 }
3401
3402 /*
3403 * No need to synchronize SRCU here! The caller does not rely
3404 * on all contexts being able to see the new console before
3405 * register_console() completes.
3406 */
3407
3408 console_sysfs_notify();
3409
3410 /*
3411 * By unregistering the bootconsoles after we enable the real console
3412 * we get the "console xxx enabled" message on all the consoles -
3413 * boot consoles, real consoles, etc - this is to ensure that end
3414 * users know there might be something in the kernel's log buffer that
3415 * went to the bootconsole (that they do not see on the real console)
3416 */
3417 con_printk(KERN_INFO, newcon, "enabled\n");
3418 if (bootcon_registered &&
3419 ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) &&
3420 !keep_bootcon) {
3421 struct hlist_node *tmp;
3422
3423 hlist_for_each_entry_safe(con, tmp, &console_list, node) {
3424 if (con->flags & CON_BOOT)
3425 unregister_console_locked(con);
3426 }
3427 }
3428unlock:
3429 console_list_unlock();
3430}
3431EXPORT_SYMBOL(register_console);
3432
3433/* Must be called under console_list_lock(). */
3434static int unregister_console_locked(struct console *console)
3435{
3436 int res;
3437
3438 lockdep_assert_console_list_lock_held();
3439
3440 con_printk(KERN_INFO, console, "disabled\n");
3441
3442 res = _braille_unregister_console(console);
3443 if (res < 0)
3444 return res;
3445 if (res > 0)
3446 return 0;
3447
3448 /* Disable it unconditionally */
3449 console_srcu_write_flags(console, console->flags & ~CON_ENABLED);
3450
3451 if (!console_is_registered_locked(console))
3452 return -ENODEV;
3453
3454 hlist_del_init_rcu(&console->node);
3455
3456 /*
3457 * <HISTORICAL>
3458 * If this isn't the last console and it has CON_CONSDEV set, we
3459 * need to set it on the next preferred console.
3460 * </HISTORICAL>
3461 *
3462 * The above makes no sense as there is no guarantee that the next
3463 * console has any device attached. Oh well....
3464 */
3465 if (!hlist_empty(&console_list) && console->flags & CON_CONSDEV)
3466 console_srcu_write_flags(console_first(), console_first()->flags | CON_CONSDEV);
3467
3468 /*
3469 * Ensure that all SRCU list walks have completed. All contexts
3470 * must not be able to see this console in the list so that any
3471 * exit/cleanup routines can be performed safely.
3472 */
3473 synchronize_srcu(&console_srcu);
3474
3475 console_sysfs_notify();
3476
3477 if (console->exit)
3478 res = console->exit(console);
3479
3480 return res;
3481}
3482
3483int unregister_console(struct console *console)
3484{
3485 int res;
3486
3487 console_list_lock();
3488 res = unregister_console_locked(console);
3489 console_list_unlock();
3490 return res;
3491}
3492EXPORT_SYMBOL(unregister_console);
3493
3494/**
3495 * console_force_preferred_locked - force a registered console preferred
3496 * @con: The registered console to force preferred.
3497 *
3498 * Must be called under console_list_lock().
3499 */
3500void console_force_preferred_locked(struct console *con)
3501{
3502 struct console *cur_pref_con;
3503
3504 if (!console_is_registered_locked(con))
3505 return;
3506
3507 cur_pref_con = console_first();
3508
3509 /* Already preferred? */
3510 if (cur_pref_con == con)
3511 return;
3512
3513 /*
3514 * Delete, but do not re-initialize the entry. This allows the console
3515 * to continue to appear registered (via any hlist_unhashed_lockless()
3516 * checks), even though it was briefly removed from the console list.
3517 */
3518 hlist_del_rcu(&con->node);
3519
3520 /*
3521 * Ensure that all SRCU list walks have completed so that the console
3522 * can be added to the beginning of the console list and its forward
3523 * list pointer can be re-initialized.
3524 */
3525 synchronize_srcu(&console_srcu);
3526
3527 con->flags |= CON_CONSDEV;
3528 WARN_ON(!con->device);
3529
3530 /* Only the new head can have CON_CONSDEV set. */
3531 console_srcu_write_flags(cur_pref_con, cur_pref_con->flags & ~CON_CONSDEV);
3532 hlist_add_head_rcu(&con->node, &console_list);
3533}
3534EXPORT_SYMBOL(console_force_preferred_locked);
3535
3536/*
3537 * Initialize the console device. This is called *early*, so
3538 * we can't necessarily depend on lots of kernel help here.
3539 * Just do some early initializations, and do the complex setup
3540 * later.
3541 */
3542void __init console_init(void)
3543{
3544 int ret;
3545 initcall_t call;
3546 initcall_entry_t *ce;
3547
3548 /* Setup the default TTY line discipline. */
3549 n_tty_init();
3550
3551 /*
3552 * set up the console device so that later boot sequences can
3553 * inform about problems etc..
3554 */
3555 ce = __con_initcall_start;
3556 trace_initcall_level("console");
3557 while (ce < __con_initcall_end) {
3558 call = initcall_from_entry(ce);
3559 trace_initcall_start(call);
3560 ret = call();
3561 trace_initcall_finish(call, ret);
3562 ce++;
3563 }
3564}
3565
3566/*
3567 * Some boot consoles access data that is in the init section and which will
3568 * be discarded after the initcalls have been run. To make sure that no code
3569 * will access this data, unregister the boot consoles in a late initcall.
3570 *
3571 * If for some reason, such as deferred probe or the driver being a loadable
3572 * module, the real console hasn't registered yet at this point, there will
3573 * be a brief interval in which no messages are logged to the console, which
3574 * makes it difficult to diagnose problems that occur during this time.
3575 *
3576 * To mitigate this problem somewhat, only unregister consoles whose memory
3577 * intersects with the init section. Note that all other boot consoles will
3578 * get unregistered when the real preferred console is registered.
3579 */
3580static int __init printk_late_init(void)
3581{
3582 struct hlist_node *tmp;
3583 struct console *con;
3584 int ret;
3585
3586 console_list_lock();
3587 hlist_for_each_entry_safe(con, tmp, &console_list, node) {
3588 if (!(con->flags & CON_BOOT))
3589 continue;
3590
3591 /* Check addresses that might be used for enabled consoles. */
3592 if (init_section_intersects(con, sizeof(*con)) ||
3593 init_section_contains(con->write, 0) ||
3594 init_section_contains(con->read, 0) ||
3595 init_section_contains(con->device, 0) ||
3596 init_section_contains(con->unblank, 0) ||
3597 init_section_contains(con->data, 0)) {
3598 /*
3599 * Please, consider moving the reported consoles out
3600 * of the init section.
3601 */
3602 pr_warn("bootconsole [%s%d] uses init memory and must be disabled even before the real one is ready\n",
3603 con->name, con->index);
3604 unregister_console_locked(con);
3605 }
3606 }
3607 console_list_unlock();
3608
3609 ret = cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD, "printk:dead", NULL,
3610 console_cpu_notify);
3611 WARN_ON(ret < 0);
3612 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "printk:online",
3613 console_cpu_notify, NULL);
3614 WARN_ON(ret < 0);
3615 printk_sysctl_init();
3616 return 0;
3617}
3618late_initcall(printk_late_init);
3619
3620#if defined CONFIG_PRINTK
3621/* If @con is specified, only wait for that console. Otherwise wait for all. */
3622static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress)
3623{
3624 int remaining = timeout_ms;
3625 struct console *c;
3626 u64 last_diff = 0;
3627 u64 printk_seq;
3628 int cookie;
3629 u64 diff;
3630 u64 seq;
3631
3632 might_sleep();
3633
3634 seq = prb_next_seq(prb);
3635
3636 for (;;) {
3637 diff = 0;
3638
3639 /*
3640 * Hold the console_lock to guarantee safe access to
3641 * console->seq and to prevent changes to @console_suspended
3642 * until all consoles have been processed.
3643 */
3644 console_lock();
3645
3646 cookie = console_srcu_read_lock();
3647 for_each_console_srcu(c) {
3648 if (con && con != c)
3649 continue;
3650 if (!console_is_usable(c))
3651 continue;
3652 printk_seq = c->seq;
3653 if (printk_seq < seq)
3654 diff += seq - printk_seq;
3655 }
3656 console_srcu_read_unlock(cookie);
3657
3658 /*
3659 * If consoles are suspended, it cannot be expected that they
3660 * make forward progress, so timeout immediately. @diff is
3661 * still used to return a valid flush status.
3662 */
3663 if (console_suspended)
3664 remaining = 0;
3665 else if (diff != last_diff && reset_on_progress)
3666 remaining = timeout_ms;
3667
3668 console_unlock();
3669
3670 if (diff == 0 || remaining == 0)
3671 break;
3672
3673 if (remaining < 0) {
3674 /* no timeout limit */
3675 msleep(100);
3676 } else if (remaining < 100) {
3677 msleep(remaining);
3678 remaining = 0;
3679 } else {
3680 msleep(100);
3681 remaining -= 100;
3682 }
3683
3684 last_diff = diff;
3685 }
3686
3687 return (diff == 0);
3688}
3689
3690/**
3691 * pr_flush() - Wait for printing threads to catch up.
3692 *
3693 * @timeout_ms: The maximum time (in ms) to wait.
3694 * @reset_on_progress: Reset the timeout if forward progress is seen.
3695 *
3696 * A value of 0 for @timeout_ms means no waiting will occur. A value of -1
3697 * represents infinite waiting.
3698 *
3699 * If @reset_on_progress is true, the timeout will be reset whenever any
3700 * printer has been seen to make some forward progress.
3701 *
3702 * Context: Process context. May sleep while acquiring console lock.
3703 * Return: true if all enabled printers are caught up.
3704 */
3705static bool pr_flush(int timeout_ms, bool reset_on_progress)
3706{
3707 return __pr_flush(NULL, timeout_ms, reset_on_progress);
3708}
3709
3710/*
3711 * Delayed printk version, for scheduler-internal messages:
3712 */
3713#define PRINTK_PENDING_WAKEUP 0x01
3714#define PRINTK_PENDING_OUTPUT 0x02
3715
3716static DEFINE_PER_CPU(int, printk_pending);
3717
3718static void wake_up_klogd_work_func(struct irq_work *irq_work)
3719{
3720 int pending = this_cpu_xchg(printk_pending, 0);
3721
3722 if (pending & PRINTK_PENDING_OUTPUT) {
3723 /* If trylock fails, someone else is doing the printing */
3724 if (console_trylock())
3725 console_unlock();
3726 }
3727
3728 if (pending & PRINTK_PENDING_WAKEUP)
3729 wake_up_interruptible(&log_wait);
3730}
3731
3732static DEFINE_PER_CPU(struct irq_work, wake_up_klogd_work) =
3733 IRQ_WORK_INIT_LAZY(wake_up_klogd_work_func);
3734
3735static void __wake_up_klogd(int val)
3736{
3737 if (!printk_percpu_data_ready())
3738 return;
3739
3740 preempt_disable();
3741 /*
3742 * Guarantee any new records can be seen by tasks preparing to wait
3743 * before this context checks if the wait queue is empty.
3744 *
3745 * The full memory barrier within wq_has_sleeper() pairs with the full
3746 * memory barrier within set_current_state() of
3747 * prepare_to_wait_event(), which is called after ___wait_event() adds
3748 * the waiter but before it has checked the wait condition.
3749 *
3750 * This pairs with devkmsg_read:A and syslog_print:A.
3751 */
3752 if (wq_has_sleeper(&log_wait) || /* LMM(__wake_up_klogd:A) */
3753 (val & PRINTK_PENDING_OUTPUT)) {
3754 this_cpu_or(printk_pending, val);
3755 irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
3756 }
3757 preempt_enable();
3758}
3759
3760void wake_up_klogd(void)
3761{
3762 __wake_up_klogd(PRINTK_PENDING_WAKEUP);
3763}
3764
3765void defer_console_output(void)
3766{
3767 /*
3768 * New messages may have been added directly to the ringbuffer
3769 * using vprintk_store(), so wake any waiters as well.
3770 */
3771 __wake_up_klogd(PRINTK_PENDING_WAKEUP | PRINTK_PENDING_OUTPUT);
3772}
3773
3774void printk_trigger_flush(void)
3775{
3776 defer_console_output();
3777}
3778
3779int vprintk_deferred(const char *fmt, va_list args)
3780{
3781 int r;
3782
3783 r = vprintk_emit(0, LOGLEVEL_SCHED, NULL, fmt, args);
3784 defer_console_output();
3785
3786 return r;
3787}
3788
3789int _printk_deferred(const char *fmt, ...)
3790{
3791 va_list args;
3792 int r;
3793
3794 va_start(args, fmt);
3795 r = vprintk_deferred(fmt, args);
3796 va_end(args);
3797
3798 return r;
3799}
3800
3801/*
3802 * printk rate limiting, lifted from the networking subsystem.
3803 *
3804 * This enforces a rate limit: not more than 10 kernel messages
3805 * every 5s to make a denial-of-service attack impossible.
3806 */
3807DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
3808
3809int __printk_ratelimit(const char *func)
3810{
3811 return ___ratelimit(&printk_ratelimit_state, func);
3812}
3813EXPORT_SYMBOL(__printk_ratelimit);
3814
3815/**
3816 * printk_timed_ratelimit - caller-controlled printk ratelimiting
3817 * @caller_jiffies: pointer to caller's state
3818 * @interval_msecs: minimum interval between prints
3819 *
3820 * printk_timed_ratelimit() returns true if more than @interval_msecs
3821 * milliseconds have elapsed since the last time printk_timed_ratelimit()
3822 * returned true.
3823 */
3824bool printk_timed_ratelimit(unsigned long *caller_jiffies,
3825 unsigned int interval_msecs)
3826{
3827 unsigned long elapsed = jiffies - *caller_jiffies;
3828
3829 if (*caller_jiffies && elapsed <= msecs_to_jiffies(interval_msecs))
3830 return false;
3831
3832 *caller_jiffies = jiffies;
3833 return true;
3834}
3835EXPORT_SYMBOL(printk_timed_ratelimit);
3836
3837static DEFINE_SPINLOCK(dump_list_lock);
3838static LIST_HEAD(dump_list);
3839
3840/**
3841 * kmsg_dump_register - register a kernel log dumper.
3842 * @dumper: pointer to the kmsg_dumper structure
3843 *
3844 * Adds a kernel log dumper to the system. The dump callback in the
3845 * structure will be called when the kernel oopses or panics and must be
3846 * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
3847 */
3848int kmsg_dump_register(struct kmsg_dumper *dumper)
3849{
3850 unsigned long flags;
3851 int err = -EBUSY;
3852
3853 /* The dump callback needs to be set */
3854 if (!dumper->dump)
3855 return -EINVAL;
3856
3857 spin_lock_irqsave(&dump_list_lock, flags);
3858 /* Don't allow registering multiple times */
3859 if (!dumper->registered) {
3860 dumper->registered = 1;
3861 list_add_tail_rcu(&dumper->list, &dump_list);
3862 err = 0;
3863 }
3864 spin_unlock_irqrestore(&dump_list_lock, flags);
3865
3866 return err;
3867}
3868EXPORT_SYMBOL_GPL(kmsg_dump_register);
3869
3870/**
3871 * kmsg_dump_unregister - unregister a kmsg dumper.
3872 * @dumper: pointer to the kmsg_dumper structure
3873 *
3874 * Removes a dump device from the system. Returns zero on success and
3875 * %-EINVAL otherwise.
3876 */
3877int kmsg_dump_unregister(struct kmsg_dumper *dumper)
3878{
3879 unsigned long flags;
3880 int err = -EINVAL;
3881
3882 spin_lock_irqsave(&dump_list_lock, flags);
3883 if (dumper->registered) {
3884 dumper->registered = 0;
3885 list_del_rcu(&dumper->list);
3886 err = 0;
3887 }
3888 spin_unlock_irqrestore(&dump_list_lock, flags);
3889 synchronize_rcu();
3890
3891 return err;
3892}
3893EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
3894
3895static bool always_kmsg_dump;
3896module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);
3897
3898const char *kmsg_dump_reason_str(enum kmsg_dump_reason reason)
3899{
3900 switch (reason) {
3901 case KMSG_DUMP_PANIC:
3902 return "Panic";
3903 case KMSG_DUMP_OOPS:
3904 return "Oops";
3905 case KMSG_DUMP_EMERG:
3906 return "Emergency";
3907 case KMSG_DUMP_SHUTDOWN:
3908 return "Shutdown";
3909 default:
3910 return "Unknown";
3911 }
3912}
3913EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
3914
3915/**
3916 * kmsg_dump - dump kernel log to kernel message dumpers.
3917 * @reason: the reason (oops, panic etc) for dumping
3918 *
3919 * Call each of the registered dumper's dump() callback, which can
3920 * retrieve the kmsg records with kmsg_dump_get_line() or
3921 * kmsg_dump_get_buffer().
3922 */
3923void kmsg_dump(enum kmsg_dump_reason reason)
3924{
3925 struct kmsg_dumper *dumper;
3926
3927 rcu_read_lock();
3928 list_for_each_entry_rcu(dumper, &dump_list, list) {
3929 enum kmsg_dump_reason max_reason = dumper->max_reason;
3930
3931 /*
3932 * If client has not provided a specific max_reason, default
3933 * to KMSG_DUMP_OOPS, unless always_kmsg_dump was set.
3934 */
3935 if (max_reason == KMSG_DUMP_UNDEF) {
3936 max_reason = always_kmsg_dump ? KMSG_DUMP_MAX :
3937 KMSG_DUMP_OOPS;
3938 }
3939 if (reason > max_reason)
3940 continue;
3941
3942 /* invoke dumper which will iterate over records */
3943 dumper->dump(dumper, reason);
3944 }
3945 rcu_read_unlock();
3946}
3947
3948/**
3949 * kmsg_dump_get_line - retrieve one kmsg log line
3950 * @iter: kmsg dump iterator
3951 * @syslog: include the "<4>" prefixes
3952 * @line: buffer to copy the line to
3953 * @size: maximum size of the buffer
3954 * @len: length of line placed into buffer
3955 *
3956 * Start at the beginning of the kmsg buffer, with the oldest kmsg
3957 * record, and copy one record into the provided buffer.
3958 *
3959 * Consecutive calls will return the next available record moving
3960 * towards the end of the buffer with the youngest messages.
3961 *
3962 * A return value of FALSE indicates that there are no more records to
3963 * read.
3964 */
3965bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
3966 char *line, size_t size, size_t *len)
3967{
3968 u64 min_seq = latched_seq_read_nolock(&clear_seq);
3969 struct printk_info info;
3970 unsigned int line_count;
3971 struct printk_record r;
3972 size_t l = 0;
3973 bool ret = false;
3974
3975 if (iter->cur_seq < min_seq)
3976 iter->cur_seq = min_seq;
3977
3978 prb_rec_init_rd(&r, &info, line, size);
3979
3980 /* Read text or count text lines? */
3981 if (line) {
3982 if (!prb_read_valid(prb, iter->cur_seq, &r))
3983 goto out;
3984 l = record_print_text(&r, syslog, printk_time);
3985 } else {
3986 if (!prb_read_valid_info(prb, iter->cur_seq,
3987 &info, &line_count)) {
3988 goto out;
3989 }
3990 l = get_record_print_text_size(&info, line_count, syslog,
3991 printk_time);
3992
3993 }
3994
3995 iter->cur_seq = r.info->seq + 1;
3996 ret = true;
3997out:
3998 if (len)
3999 *len = l;
4000 return ret;
4001}
4002EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
4003
4004/**
4005 * kmsg_dump_get_buffer - copy kmsg log lines
4006 * @iter: kmsg dump iterator
4007 * @syslog: include the "<4>" prefixes
4008 * @buf: buffer to copy the line to
4009 * @size: maximum size of the buffer
4010 * @len_out: length of line placed into buffer
4011 *
4012 * Start at the end of the kmsg buffer and fill the provided buffer
4013 * with as many of the *youngest* kmsg records that fit into it.
4014 * If the buffer is large enough, all available kmsg records will be
4015 * copied with a single call.
4016 *
4017 * Consecutive calls will fill the buffer with the next block of
4018 * available older records, not including the earlier retrieved ones.
4019 *
4020 * A return value of FALSE indicates that there are no more records to
4021 * read.
4022 */
4023bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
4024 char *buf, size_t size, size_t *len_out)
4025{
4026 u64 min_seq = latched_seq_read_nolock(&clear_seq);
4027 struct printk_info info;
4028 struct printk_record r;
4029 u64 seq;
4030 u64 next_seq;
4031 size_t len = 0;
4032 bool ret = false;
4033 bool time = printk_time;
4034
4035 if (!buf || !size)
4036 goto out;
4037
4038 if (iter->cur_seq < min_seq)
4039 iter->cur_seq = min_seq;
4040
4041 if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
4042 if (info.seq != iter->cur_seq) {
4043 /* messages are gone, move to first available one */
4044 iter->cur_seq = info.seq;
4045 }
4046 }
4047
4048 /* last entry */
4049 if (iter->cur_seq >= iter->next_seq)
4050 goto out;
4051
4052 /*
4053 * Find first record that fits, including all following records,
4054 * into the user-provided buffer for this dump. Pass in size-1
4055 * because this function (by way of record_print_text()) will
4056 * not write more than size-1 bytes of text into @buf.
4057 */
4058 seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,
4059 size - 1, syslog, time);
4060
4061 /*
4062 * Next kmsg_dump_get_buffer() invocation will dump block of
4063 * older records stored right before this one.
4064 */
4065 next_seq = seq;
4066
4067 prb_rec_init_rd(&r, &info, buf, size);
4068
4069 len = 0;
4070 prb_for_each_record(seq, prb, seq, &r) {
4071 if (r.info->seq >= iter->next_seq)
4072 break;
4073
4074 len += record_print_text(&r, syslog, time);
4075
4076 /* Adjust record to store to remaining buffer space. */
4077 prb_rec_init_rd(&r, &info, buf + len, size - len);
4078 }
4079
4080 iter->next_seq = next_seq;
4081 ret = true;
4082out:
4083 if (len_out)
4084 *len_out = len;
4085 return ret;
4086}
4087EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
4088
4089/**
4090 * kmsg_dump_rewind - reset the iterator
4091 * @iter: kmsg dump iterator
4092 *
4093 * Reset the dumper's iterator so that kmsg_dump_get_line() and
4094 * kmsg_dump_get_buffer() can be called again and used multiple
4095 * times within the same dumper.dump() callback.
4096 */
4097void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
4098{
4099 iter->cur_seq = latched_seq_read_nolock(&clear_seq);
4100 iter->next_seq = prb_next_seq(prb);
4101}
4102EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
4103
4104#endif
4105
4106#ifdef CONFIG_SMP
4107static atomic_t printk_cpu_sync_owner = ATOMIC_INIT(-1);
4108static atomic_t printk_cpu_sync_nested = ATOMIC_INIT(0);
4109
4110/**
4111 * __printk_cpu_sync_wait() - Busy wait until the printk cpu-reentrant
4112 * spinning lock is not owned by any CPU.
4113 *
4114 * Context: Any context.
4115 */
4116void __printk_cpu_sync_wait(void)
4117{
4118 do {
4119 cpu_relax();
4120 } while (atomic_read(&printk_cpu_sync_owner) != -1);
4121}
4122EXPORT_SYMBOL(__printk_cpu_sync_wait);
4123
4124/**
4125 * __printk_cpu_sync_try_get() - Try to acquire the printk cpu-reentrant
4126 * spinning lock.
4127 *
4128 * If no processor has the lock, the calling processor takes the lock and
4129 * becomes the owner. If the calling processor is already the owner of the
4130 * lock, this function succeeds immediately.
4131 *
4132 * Context: Any context. Expects interrupts to be disabled.
4133 * Return: 1 on success, otherwise 0.
4134 */
4135int __printk_cpu_sync_try_get(void)
4136{
4137 int cpu;
4138 int old;
4139
4140 cpu = smp_processor_id();
4141
4142 /*
4143 * Guarantee loads and stores from this CPU when it is the lock owner
4144 * are _not_ visible to the previous lock owner. This pairs with
4145 * __printk_cpu_sync_put:B.
4146 *
4147 * Memory barrier involvement:
4148 *
4149 * If __printk_cpu_sync_try_get:A reads from __printk_cpu_sync_put:B,
4150 * then __printk_cpu_sync_put:A can never read from
4151 * __printk_cpu_sync_try_get:B.
4152 *
4153 * Relies on:
4154 *
4155 * RELEASE from __printk_cpu_sync_put:A to __printk_cpu_sync_put:B
4156 * of the previous CPU
4157 * matching
4158 * ACQUIRE from __printk_cpu_sync_try_get:A to
4159 * __printk_cpu_sync_try_get:B of this CPU
4160 */
4161 old = atomic_cmpxchg_acquire(&printk_cpu_sync_owner, -1,
4162 cpu); /* LMM(__printk_cpu_sync_try_get:A) */
4163 if (old == -1) {
4164 /*
4165 * This CPU is now the owner and begins loading/storing
4166 * data: LMM(__printk_cpu_sync_try_get:B)
4167 */
4168 return 1;
4169
4170 } else if (old == cpu) {
4171 /* This CPU is already the owner. */
4172 atomic_inc(&printk_cpu_sync_nested);
4173 return 1;
4174 }
4175
4176 return 0;
4177}
4178EXPORT_SYMBOL(__printk_cpu_sync_try_get);
4179
4180/**
4181 * __printk_cpu_sync_put() - Release the printk cpu-reentrant spinning lock.
4182 *
4183 * The calling processor must be the owner of the lock.
4184 *
4185 * Context: Any context. Expects interrupts to be disabled.
4186 */
4187void __printk_cpu_sync_put(void)
4188{
4189 if (atomic_read(&printk_cpu_sync_nested)) {
4190 atomic_dec(&printk_cpu_sync_nested);
4191 return;
4192 }
4193
4194 /*
4195 * This CPU is finished loading/storing data:
4196 * LMM(__printk_cpu_sync_put:A)
4197 */
4198
4199 /*
4200 * Guarantee loads and stores from this CPU when it was the
4201 * lock owner are visible to the next lock owner. This pairs
4202 * with __printk_cpu_sync_try_get:A.
4203 *
4204 * Memory barrier involvement:
4205 *
4206 * If __printk_cpu_sync_try_get:A reads from __printk_cpu_sync_put:B,
4207 * then __printk_cpu_sync_try_get:B reads from __printk_cpu_sync_put:A.
4208 *
4209 * Relies on:
4210 *
4211 * RELEASE from __printk_cpu_sync_put:A to __printk_cpu_sync_put:B
4212 * of this CPU
4213 * matching
4214 * ACQUIRE from __printk_cpu_sync_try_get:A to
4215 * __printk_cpu_sync_try_get:B of the next CPU
4216 */
4217 atomic_set_release(&printk_cpu_sync_owner,
4218 -1); /* LMM(__printk_cpu_sync_put:B) */
4219}
4220EXPORT_SYMBOL(__printk_cpu_sync_put);
4221#endif /* CONFIG_SMP */