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TOMOYO Linux Cross Reference
Linux/kernel/printk/printk.c

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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/crash_core.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 #include <linux/sched/clock.h>
 49 #include <linux/sched/debug.h>
 50 #include <linux/sched/task_stack.h>
 51 
 52 #include <linux/uaccess.h>
 53 #include <asm/sections.h>
 54 
 55 #define CREATE_TRACE_POINTS
 56 #include <trace/events/printk.h>
 57 
 58 #include "console_cmdline.h"
 59 #include "braille.h"
 60 #include "internal.h"
 61 
 62 int console_printk[4] = {
 63         CONSOLE_LOGLEVEL_DEFAULT,       /* console_loglevel */
 64         MESSAGE_LOGLEVEL_DEFAULT,       /* default_message_loglevel */
 65         CONSOLE_LOGLEVEL_MIN,           /* minimum_console_loglevel */
 66         CONSOLE_LOGLEVEL_DEFAULT,       /* default_console_loglevel */
 67 };
 68 
 69 /*
 70  * Low level drivers may need that to know if they can schedule in
 71  * their unblank() callback or not. So let's export it.
 72  */
 73 int oops_in_progress;
 74 EXPORT_SYMBOL(oops_in_progress);
 75 
 76 /*
 77  * console_sem protects the console_drivers list, and also
 78  * provides serialisation for access to the entire console
 79  * driver system.
 80  */
 81 static DEFINE_SEMAPHORE(console_sem);
 82 struct console *console_drivers;
 83 EXPORT_SYMBOL_GPL(console_drivers);
 84 
 85 #ifdef CONFIG_LOCKDEP
 86 static struct lockdep_map console_lock_dep_map = {
 87         .name = "console_lock"
 88 };
 89 #endif
 90 
 91 enum devkmsg_log_bits {
 92         __DEVKMSG_LOG_BIT_ON = 0,
 93         __DEVKMSG_LOG_BIT_OFF,
 94         __DEVKMSG_LOG_BIT_LOCK,
 95 };
 96 
 97 enum devkmsg_log_masks {
 98         DEVKMSG_LOG_MASK_ON             = BIT(__DEVKMSG_LOG_BIT_ON),
 99         DEVKMSG_LOG_MASK_OFF            = BIT(__DEVKMSG_LOG_BIT_OFF),
100         DEVKMSG_LOG_MASK_LOCK           = BIT(__DEVKMSG_LOG_BIT_LOCK),
101 };
102 
103 /* Keep both the 'on' and 'off' bits clear, i.e. ratelimit by default: */
104 #define DEVKMSG_LOG_MASK_DEFAULT        0
105 
106 static unsigned int __read_mostly devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
107 
108 static int __control_devkmsg(char *str)
109 {
110         if (!str)
111                 return -EINVAL;
112 
113         if (!strncmp(str, "on", 2)) {
114                 devkmsg_log = DEVKMSG_LOG_MASK_ON;
115                 return 2;
116         } else if (!strncmp(str, "off", 3)) {
117                 devkmsg_log = DEVKMSG_LOG_MASK_OFF;
118                 return 3;
119         } else if (!strncmp(str, "ratelimit", 9)) {
120                 devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
121                 return 9;
122         }
123         return -EINVAL;
124 }
125 
126 static int __init control_devkmsg(char *str)
127 {
128         if (__control_devkmsg(str) < 0)
129                 return 1;
130 
131         /*
132          * Set sysctl string accordingly:
133          */
134         if (devkmsg_log == DEVKMSG_LOG_MASK_ON)
135                 strcpy(devkmsg_log_str, "on");
136         else if (devkmsg_log == DEVKMSG_LOG_MASK_OFF)
137                 strcpy(devkmsg_log_str, "off");
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 
152 char devkmsg_log_str[DEVKMSG_STR_MAX_SIZE] = "ratelimit";
153 
154 int 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  */
203 static 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 
214 static int __down_trylock_console_sem(unsigned long ip)
215 {
216         int lock_failed;
217         unsigned long flags;
218 
219         /*
220          * Here and in __up_console_sem() we need to be in safe mode,
221          * because spindump/WARN/etc from under console ->lock will
222          * deadlock in printk()->down_trylock_console_sem() otherwise.
223          */
224         printk_safe_enter_irqsave(flags);
225         lock_failed = down_trylock(&console_sem);
226         printk_safe_exit_irqrestore(flags);
227 
228         if (lock_failed)
229                 return 1;
230         mutex_acquire(&console_lock_dep_map, 0, 1, ip);
231         return 0;
232 }
233 #define down_trylock_console_sem() __down_trylock_console_sem(_RET_IP_)
234 
235 static void __up_console_sem(unsigned long ip)
236 {
237         unsigned long flags;
238 
239         mutex_release(&console_lock_dep_map, 1, ip);
240 
241         printk_safe_enter_irqsave(flags);
242         up(&console_sem);
243         printk_safe_exit_irqrestore(flags);
244 }
245 #define up_console_sem() __up_console_sem(_RET_IP_)
246 
247 /*
248  * This is used for debugging the mess that is the VT code by
249  * keeping track if we have the console semaphore held. It's
250  * definitely not the perfect debug tool (we don't know if _WE_
251  * hold it and are racing, but it helps tracking those weird code
252  * paths in the console code where we end up in places I want
253  * locked without the console sempahore held).
254  */
255 static int console_locked, console_suspended;
256 
257 /*
258  * If exclusive_console is non-NULL then only this console is to be printed to.
259  */
260 static struct console *exclusive_console;
261 
262 /*
263  *      Array of consoles built from command line options (console=)
264  */
265 
266 #define MAX_CMDLINECONSOLES 8
267 
268 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
269 
270 static int preferred_console = -1;
271 int console_set_on_cmdline;
272 EXPORT_SYMBOL(console_set_on_cmdline);
273 
274 /* Flag: console code may call schedule() */
275 static int console_may_schedule;
276 
277 enum con_msg_format_flags {
278         MSG_FORMAT_DEFAULT      = 0,
279         MSG_FORMAT_SYSLOG       = (1 << 0),
280 };
281 
282 static int console_msg_format = MSG_FORMAT_DEFAULT;
283 
284 /*
285  * The printk log buffer consists of a chain of concatenated variable
286  * length records. Every record starts with a record header, containing
287  * the overall length of the record.
288  *
289  * The heads to the first and last entry in the buffer, as well as the
290  * sequence numbers of these entries are maintained when messages are
291  * stored.
292  *
293  * If the heads indicate available messages, the length in the header
294  * tells the start next message. A length == 0 for the next message
295  * indicates a wrap-around to the beginning of the buffer.
296  *
297  * Every record carries the monotonic timestamp in microseconds, as well as
298  * the standard userspace syslog level and syslog facility. The usual
299  * kernel messages use LOG_KERN; userspace-injected messages always carry
300  * a matching syslog facility, by default LOG_USER. The origin of every
301  * message can be reliably determined that way.
302  *
303  * The human readable log message directly follows the message header. The
304  * length of the message text is stored in the header, the stored message
305  * is not terminated.
306  *
307  * Optionally, a message can carry a dictionary of properties (key/value pairs),
308  * to provide userspace with a machine-readable message context.
309  *
310  * Examples for well-defined, commonly used property names are:
311  *   DEVICE=b12:8               device identifier
312  *                                b12:8         block dev_t
313  *                                c127:3        char dev_t
314  *                                n8            netdev ifindex
315  *                                +sound:card0  subsystem:devname
316  *   SUBSYSTEM=pci              driver-core subsystem name
317  *
318  * Valid characters in property names are [a-zA-Z0-9.-_]. The plain text value
319  * follows directly after a '=' character. Every property is terminated by
320  * a '\0' character. The last property is not terminated.
321  *
322  * Example of a message structure:
323  *   0000  ff 8f 00 00 00 00 00 00      monotonic time in nsec
324  *   0008  34 00                        record is 52 bytes long
325  *   000a        0b 00                  text is 11 bytes long
326  *   000c              1f 00            dictionary is 23 bytes long
327  *   000e                    03 00      LOG_KERN (facility) LOG_ERR (level)
328  *   0010  69 74 27 73 20 61 20 6c      "it's a l"
329  *         69 6e 65                     "ine"
330  *   001b           44 45 56 49 43      "DEVIC"
331  *         45 3d 62 38 3a 32 00 44      "E=b8:2\0D"
332  *         52 49 56 45 52 3d 62 75      "RIVER=bu"
333  *         67                           "g"
334  *   0032     00 00 00                  padding to next message header
335  *
336  * The 'struct printk_log' buffer header must never be directly exported to
337  * userspace, it is a kernel-private implementation detail that might
338  * need to be changed in the future, when the requirements change.
339  *
340  * /dev/kmsg exports the structured data in the following line format:
341  *   "<level>,<sequnum>,<timestamp>,<contflag>[,additional_values, ... ];<message text>\n"
342  *
343  * Users of the export format should ignore possible additional values
344  * separated by ',', and find the message after the ';' character.
345  *
346  * The optional key/value pairs are attached as continuation lines starting
347  * with a space character and terminated by a newline. All possible
348  * non-prinatable characters are escaped in the "\xff" notation.
349  */
350 
351 enum log_flags {
352         LOG_NOCONS      = 1,    /* already flushed, do not print to console */
353         LOG_NEWLINE     = 2,    /* text ended with a newline */
354         LOG_PREFIX      = 4,    /* text started with a prefix */
355         LOG_CONT        = 8,    /* text is a fragment of a continuation line */
356 };
357 
358 struct printk_log {
359         u64 ts_nsec;            /* timestamp in nanoseconds */
360         u16 len;                /* length of entire record */
361         u16 text_len;           /* length of text buffer */
362         u16 dict_len;           /* length of dictionary buffer */
363         u8 facility;            /* syslog facility */
364         u8 flags:5;             /* internal record flags */
365         u8 level:3;             /* syslog level */
366 }
367 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
368 __packed __aligned(4)
369 #endif
370 ;
371 
372 /*
373  * The logbuf_lock protects kmsg buffer, indices, counters.  This can be taken
374  * within the scheduler's rq lock. It must be released before calling
375  * console_unlock() or anything else that might wake up a process.
376  */
377 DEFINE_RAW_SPINLOCK(logbuf_lock);
378 
379 /*
380  * Helper macros to lock/unlock logbuf_lock and switch between
381  * printk-safe/unsafe modes.
382  */
383 #define logbuf_lock_irq()                               \
384         do {                                            \
385                 printk_safe_enter_irq();                \
386                 raw_spin_lock(&logbuf_lock);            \
387         } while (0)
388 
389 #define logbuf_unlock_irq()                             \
390         do {                                            \
391                 raw_spin_unlock(&logbuf_lock);          \
392                 printk_safe_exit_irq();                 \
393         } while (0)
394 
395 #define logbuf_lock_irqsave(flags)                      \
396         do {                                            \
397                 printk_safe_enter_irqsave(flags);       \
398                 raw_spin_lock(&logbuf_lock);            \
399         } while (0)
400 
401 #define logbuf_unlock_irqrestore(flags)         \
402         do {                                            \
403                 raw_spin_unlock(&logbuf_lock);          \
404                 printk_safe_exit_irqrestore(flags);     \
405         } while (0)
406 
407 #ifdef CONFIG_PRINTK
408 DECLARE_WAIT_QUEUE_HEAD(log_wait);
409 /* the next printk record to read by syslog(READ) or /proc/kmsg */
410 static u64 syslog_seq;
411 static u32 syslog_idx;
412 static size_t syslog_partial;
413 
414 /* index and sequence number of the first record stored in the buffer */
415 static u64 log_first_seq;
416 static u32 log_first_idx;
417 
418 /* index and sequence number of the next record to store in the buffer */
419 static u64 log_next_seq;
420 static u32 log_next_idx;
421 
422 /* the next printk record to write to the console */
423 static u64 console_seq;
424 static u32 console_idx;
425 
426 /* the next printk record to read after the last 'clear' command */
427 static u64 clear_seq;
428 static u32 clear_idx;
429 
430 #define PREFIX_MAX              32
431 #define LOG_LINE_MAX            (1024 - PREFIX_MAX)
432 
433 #define LOG_LEVEL(v)            ((v) & 0x07)
434 #define LOG_FACILITY(v)         ((v) >> 3 & 0xff)
435 
436 /* record buffer */
437 #define LOG_ALIGN __alignof__(struct printk_log)
438 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
439 static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
440 static char *log_buf = __log_buf;
441 static u32 log_buf_len = __LOG_BUF_LEN;
442 
443 /* Return log buffer address */
444 char *log_buf_addr_get(void)
445 {
446         return log_buf;
447 }
448 
449 /* Return log buffer size */
450 u32 log_buf_len_get(void)
451 {
452         return log_buf_len;
453 }
454 
455 /* human readable text of the record */
456 static char *log_text(const struct printk_log *msg)
457 {
458         return (char *)msg + sizeof(struct printk_log);
459 }
460 
461 /* optional key/value pair dictionary attached to the record */
462 static char *log_dict(const struct printk_log *msg)
463 {
464         return (char *)msg + sizeof(struct printk_log) + msg->text_len;
465 }
466 
467 /* get record by index; idx must point to valid msg */
468 static struct printk_log *log_from_idx(u32 idx)
469 {
470         struct printk_log *msg = (struct printk_log *)(log_buf + idx);
471 
472         /*
473          * A length == 0 record is the end of buffer marker. Wrap around and
474          * read the message at the start of the buffer.
475          */
476         if (!msg->len)
477                 return (struct printk_log *)log_buf;
478         return msg;
479 }
480 
481 /* get next record; idx must point to valid msg */
482 static u32 log_next(u32 idx)
483 {
484         struct printk_log *msg = (struct printk_log *)(log_buf + idx);
485 
486         /* length == 0 indicates the end of the buffer; wrap */
487         /*
488          * A length == 0 record is the end of buffer marker. Wrap around and
489          * read the message at the start of the buffer as *this* one, and
490          * return the one after that.
491          */
492         if (!msg->len) {
493                 msg = (struct printk_log *)log_buf;
494                 return msg->len;
495         }
496         return idx + msg->len;
497 }
498 
499 /*
500  * Check whether there is enough free space for the given message.
501  *
502  * The same values of first_idx and next_idx mean that the buffer
503  * is either empty or full.
504  *
505  * If the buffer is empty, we must respect the position of the indexes.
506  * They cannot be reset to the beginning of the buffer.
507  */
508 static int logbuf_has_space(u32 msg_size, bool empty)
509 {
510         u32 free;
511 
512         if (log_next_idx > log_first_idx || empty)
513                 free = max(log_buf_len - log_next_idx, log_first_idx);
514         else
515                 free = log_first_idx - log_next_idx;
516 
517         /*
518          * We need space also for an empty header that signalizes wrapping
519          * of the buffer.
520          */
521         return free >= msg_size + sizeof(struct printk_log);
522 }
523 
524 static int log_make_free_space(u32 msg_size)
525 {
526         while (log_first_seq < log_next_seq &&
527                !logbuf_has_space(msg_size, false)) {
528                 /* drop old messages until we have enough contiguous space */
529                 log_first_idx = log_next(log_first_idx);
530                 log_first_seq++;
531         }
532 
533         if (clear_seq < log_first_seq) {
534                 clear_seq = log_first_seq;
535                 clear_idx = log_first_idx;
536         }
537 
538         /* sequence numbers are equal, so the log buffer is empty */
539         if (logbuf_has_space(msg_size, log_first_seq == log_next_seq))
540                 return 0;
541 
542         return -ENOMEM;
543 }
544 
545 /* compute the message size including the padding bytes */
546 static u32 msg_used_size(u16 text_len, u16 dict_len, u32 *pad_len)
547 {
548         u32 size;
549 
550         size = sizeof(struct printk_log) + text_len + dict_len;
551         *pad_len = (-size) & (LOG_ALIGN - 1);
552         size += *pad_len;
553 
554         return size;
555 }
556 
557 /*
558  * Define how much of the log buffer we could take at maximum. The value
559  * must be greater than two. Note that only half of the buffer is available
560  * when the index points to the middle.
561  */
562 #define MAX_LOG_TAKE_PART 4
563 static const char trunc_msg[] = "<truncated>";
564 
565 static u32 truncate_msg(u16 *text_len, u16 *trunc_msg_len,
566                         u16 *dict_len, u32 *pad_len)
567 {
568         /*
569          * The message should not take the whole buffer. Otherwise, it might
570          * get removed too soon.
571          */
572         u32 max_text_len = log_buf_len / MAX_LOG_TAKE_PART;
573         if (*text_len > max_text_len)
574                 *text_len = max_text_len;
575         /* enable the warning message */
576         *trunc_msg_len = strlen(trunc_msg);
577         /* disable the "dict" completely */
578         *dict_len = 0;
579         /* compute the size again, count also the warning message */
580         return msg_used_size(*text_len + *trunc_msg_len, 0, pad_len);
581 }
582 
583 /* insert record into the buffer, discard old ones, update heads */
584 static int log_store(int facility, int level,
585                      enum log_flags flags, u64 ts_nsec,
586                      const char *dict, u16 dict_len,
587                      const char *text, u16 text_len)
588 {
589         struct printk_log *msg;
590         u32 size, pad_len;
591         u16 trunc_msg_len = 0;
592 
593         /* number of '\0' padding bytes to next message */
594         size = msg_used_size(text_len, dict_len, &pad_len);
595 
596         if (log_make_free_space(size)) {
597                 /* truncate the message if it is too long for empty buffer */
598                 size = truncate_msg(&text_len, &trunc_msg_len,
599                                     &dict_len, &pad_len);
600                 /* survive when the log buffer is too small for trunc_msg */
601                 if (log_make_free_space(size))
602                         return 0;
603         }
604 
605         if (log_next_idx + size + sizeof(struct printk_log) > log_buf_len) {
606                 /*
607                  * This message + an additional empty header does not fit
608                  * at the end of the buffer. Add an empty header with len == 0
609                  * to signify a wrap around.
610                  */
611                 memset(log_buf + log_next_idx, 0, sizeof(struct printk_log));
612                 log_next_idx = 0;
613         }
614 
615         /* fill message */
616         msg = (struct printk_log *)(log_buf + log_next_idx);
617         memcpy(log_text(msg), text, text_len);
618         msg->text_len = text_len;
619         if (trunc_msg_len) {
620                 memcpy(log_text(msg) + text_len, trunc_msg, trunc_msg_len);
621                 msg->text_len += trunc_msg_len;
622         }
623         memcpy(log_dict(msg), dict, dict_len);
624         msg->dict_len = dict_len;
625         msg->facility = facility;
626         msg->level = level & 7;
627         msg->flags = flags & 0x1f;
628         if (ts_nsec > 0)
629                 msg->ts_nsec = ts_nsec;
630         else
631                 msg->ts_nsec = local_clock();
632         memset(log_dict(msg) + dict_len, 0, pad_len);
633         msg->len = size;
634 
635         /* insert message */
636         log_next_idx += msg->len;
637         log_next_seq++;
638 
639         return msg->text_len;
640 }
641 
642 int dmesg_restrict = IS_ENABLED(CONFIG_SECURITY_DMESG_RESTRICT);
643 
644 static int syslog_action_restricted(int type)
645 {
646         if (dmesg_restrict)
647                 return 1;
648         /*
649          * Unless restricted, we allow "read all" and "get buffer size"
650          * for everybody.
651          */
652         return type != SYSLOG_ACTION_READ_ALL &&
653                type != SYSLOG_ACTION_SIZE_BUFFER;
654 }
655 
656 static int check_syslog_permissions(int type, int source)
657 {
658         /*
659          * If this is from /proc/kmsg and we've already opened it, then we've
660          * already done the capabilities checks at open time.
661          */
662         if (source == SYSLOG_FROM_PROC && type != SYSLOG_ACTION_OPEN)
663                 goto ok;
664 
665         if (syslog_action_restricted(type)) {
666                 if (capable(CAP_SYSLOG))
667                         goto ok;
668                 /*
669                  * For historical reasons, accept CAP_SYS_ADMIN too, with
670                  * a warning.
671                  */
672                 if (capable(CAP_SYS_ADMIN)) {
673                         pr_warn_once("%s (%d): Attempt to access syslog with "
674                                      "CAP_SYS_ADMIN but no CAP_SYSLOG "
675                                      "(deprecated).\n",
676                                  current->comm, task_pid_nr(current));
677                         goto ok;
678                 }
679                 return -EPERM;
680         }
681 ok:
682         return security_syslog(type);
683 }
684 
685 static void append_char(char **pp, char *e, char c)
686 {
687         if (*pp < e)
688                 *(*pp)++ = c;
689 }
690 
691 static ssize_t msg_print_ext_header(char *buf, size_t size,
692                                     struct printk_log *msg, u64 seq)
693 {
694         u64 ts_usec = msg->ts_nsec;
695 
696         do_div(ts_usec, 1000);
697 
698         return scnprintf(buf, size, "%u,%llu,%llu,%c;",
699                        (msg->facility << 3) | msg->level, seq, ts_usec,
700                        msg->flags & LOG_CONT ? 'c' : '-');
701 }
702 
703 static ssize_t msg_print_ext_body(char *buf, size_t size,
704                                   char *dict, size_t dict_len,
705                                   char *text, size_t text_len)
706 {
707         char *p = buf, *e = buf + size;
708         size_t i;
709 
710         /* escape non-printable characters */
711         for (i = 0; i < text_len; i++) {
712                 unsigned char c = text[i];
713 
714                 if (c < ' ' || c >= 127 || c == '\\')
715                         p += scnprintf(p, e - p, "\\x%02x", c);
716                 else
717                         append_char(&p, e, c);
718         }
719         append_char(&p, e, '\n');
720 
721         if (dict_len) {
722                 bool line = true;
723 
724                 for (i = 0; i < dict_len; i++) {
725                         unsigned char c = dict[i];
726 
727                         if (line) {
728                                 append_char(&p, e, ' ');
729                                 line = false;
730                         }
731 
732                         if (c == '\0') {
733                                 append_char(&p, e, '\n');
734                                 line = true;
735                                 continue;
736                         }
737 
738                         if (c < ' ' || c >= 127 || c == '\\') {
739                                 p += scnprintf(p, e - p, "\\x%02x", c);
740                                 continue;
741                         }
742 
743                         append_char(&p, e, c);
744                 }
745                 append_char(&p, e, '\n');
746         }
747 
748         return p - buf;
749 }
750 
751 /* /dev/kmsg - userspace message inject/listen interface */
752 struct devkmsg_user {
753         u64 seq;
754         u32 idx;
755         struct ratelimit_state rs;
756         struct mutex lock;
757         char buf[CONSOLE_EXT_LOG_MAX];
758 };
759 
760 static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
761 {
762         char *buf, *line;
763         int level = default_message_loglevel;
764         int facility = 1;       /* LOG_USER */
765         struct file *file = iocb->ki_filp;
766         struct devkmsg_user *user = file->private_data;
767         size_t len = iov_iter_count(from);
768         ssize_t ret = len;
769 
770         if (!user || len > LOG_LINE_MAX)
771                 return -EINVAL;
772 
773         /* Ignore when user logging is disabled. */
774         if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
775                 return len;
776 
777         /* Ratelimit when not explicitly enabled. */
778         if (!(devkmsg_log & DEVKMSG_LOG_MASK_ON)) {
779                 if (!___ratelimit(&user->rs, current->comm))
780                         return ret;
781         }
782 
783         buf = kmalloc(len+1, GFP_KERNEL);
784         if (buf == NULL)
785                 return -ENOMEM;
786 
787         buf[len] = '\0';
788         if (!copy_from_iter_full(buf, len, from)) {
789                 kfree(buf);
790                 return -EFAULT;
791         }
792 
793         /*
794          * Extract and skip the syslog prefix <[0-9]*>. Coming from userspace
795          * the decimal value represents 32bit, the lower 3 bit are the log
796          * level, the rest are the log facility.
797          *
798          * If no prefix or no userspace facility is specified, we
799          * enforce LOG_USER, to be able to reliably distinguish
800          * kernel-generated messages from userspace-injected ones.
801          */
802         line = buf;
803         if (line[0] == '<') {
804                 char *endp = NULL;
805                 unsigned int u;
806 
807                 u = simple_strtoul(line + 1, &endp, 10);
808                 if (endp && endp[0] == '>') {
809                         level = LOG_LEVEL(u);
810                         if (LOG_FACILITY(u) != 0)
811                                 facility = LOG_FACILITY(u);
812                         endp++;
813                         len -= endp - line;
814                         line = endp;
815                 }
816         }
817 
818         printk_emit(facility, level, NULL, 0, "%s", line);
819         kfree(buf);
820         return ret;
821 }
822 
823 static ssize_t devkmsg_read(struct file *file, char __user *buf,
824                             size_t count, loff_t *ppos)
825 {
826         struct devkmsg_user *user = file->private_data;
827         struct printk_log *msg;
828         size_t len;
829         ssize_t ret;
830 
831         if (!user)
832                 return -EBADF;
833 
834         ret = mutex_lock_interruptible(&user->lock);
835         if (ret)
836                 return ret;
837 
838         logbuf_lock_irq();
839         while (user->seq == log_next_seq) {
840                 if (file->f_flags & O_NONBLOCK) {
841                         ret = -EAGAIN;
842                         logbuf_unlock_irq();
843                         goto out;
844                 }
845 
846                 logbuf_unlock_irq();
847                 ret = wait_event_interruptible(log_wait,
848                                                user->seq != log_next_seq);
849                 if (ret)
850                         goto out;
851                 logbuf_lock_irq();
852         }
853 
854         if (user->seq < log_first_seq) {
855                 /* our last seen message is gone, return error and reset */
856                 user->idx = log_first_idx;
857                 user->seq = log_first_seq;
858                 ret = -EPIPE;
859                 logbuf_unlock_irq();
860                 goto out;
861         }
862 
863         msg = log_from_idx(user->idx);
864         len = msg_print_ext_header(user->buf, sizeof(user->buf),
865                                    msg, user->seq);
866         len += msg_print_ext_body(user->buf + len, sizeof(user->buf) - len,
867                                   log_dict(msg), msg->dict_len,
868                                   log_text(msg), msg->text_len);
869 
870         user->idx = log_next(user->idx);
871         user->seq++;
872         logbuf_unlock_irq();
873 
874         if (len > count) {
875                 ret = -EINVAL;
876                 goto out;
877         }
878 
879         if (copy_to_user(buf, user->buf, len)) {
880                 ret = -EFAULT;
881                 goto out;
882         }
883         ret = len;
884 out:
885         mutex_unlock(&user->lock);
886         return ret;
887 }
888 
889 static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
890 {
891         struct devkmsg_user *user = file->private_data;
892         loff_t ret = 0;
893 
894         if (!user)
895                 return -EBADF;
896         if (offset)
897                 return -ESPIPE;
898 
899         logbuf_lock_irq();
900         switch (whence) {
901         case SEEK_SET:
902                 /* the first record */
903                 user->idx = log_first_idx;
904                 user->seq = log_first_seq;
905                 break;
906         case SEEK_DATA:
907                 /*
908                  * The first record after the last SYSLOG_ACTION_CLEAR,
909                  * like issued by 'dmesg -c'. Reading /dev/kmsg itself
910                  * changes no global state, and does not clear anything.
911                  */
912                 user->idx = clear_idx;
913                 user->seq = clear_seq;
914                 break;
915         case SEEK_END:
916                 /* after the last record */
917                 user->idx = log_next_idx;
918                 user->seq = log_next_seq;
919                 break;
920         default:
921                 ret = -EINVAL;
922         }
923         logbuf_unlock_irq();
924         return ret;
925 }
926 
927 static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
928 {
929         struct devkmsg_user *user = file->private_data;
930         __poll_t ret = 0;
931 
932         if (!user)
933                 return EPOLLERR|EPOLLNVAL;
934 
935         poll_wait(file, &log_wait, wait);
936 
937         logbuf_lock_irq();
938         if (user->seq < log_next_seq) {
939                 /* return error when data has vanished underneath us */
940                 if (user->seq < log_first_seq)
941                         ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;
942                 else
943                         ret = EPOLLIN|EPOLLRDNORM;
944         }
945         logbuf_unlock_irq();
946 
947         return ret;
948 }
949 
950 static int devkmsg_open(struct inode *inode, struct file *file)
951 {
952         struct devkmsg_user *user;
953         int err;
954 
955         if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
956                 return -EPERM;
957 
958         /* write-only does not need any file context */
959         if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
960                 err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
961                                                SYSLOG_FROM_READER);
962                 if (err)
963                         return err;
964         }
965 
966         user = kmalloc(sizeof(struct devkmsg_user), GFP_KERNEL);
967         if (!user)
968                 return -ENOMEM;
969 
970         ratelimit_default_init(&user->rs);
971         ratelimit_set_flags(&user->rs, RATELIMIT_MSG_ON_RELEASE);
972 
973         mutex_init(&user->lock);
974 
975         logbuf_lock_irq();
976         user->idx = log_first_idx;
977         user->seq = log_first_seq;
978         logbuf_unlock_irq();
979 
980         file->private_data = user;
981         return 0;
982 }
983 
984 static int devkmsg_release(struct inode *inode, struct file *file)
985 {
986         struct devkmsg_user *user = file->private_data;
987 
988         if (!user)
989                 return 0;
990 
991         ratelimit_state_exit(&user->rs);
992 
993         mutex_destroy(&user->lock);
994         kfree(user);
995         return 0;
996 }
997 
998 const struct file_operations kmsg_fops = {
999         .open = devkmsg_open,
1000         .read = devkmsg_read,
1001         .write_iter = devkmsg_write,
1002         .llseek = devkmsg_llseek,
1003         .poll = devkmsg_poll,
1004         .release = devkmsg_release,
1005 };
1006 
1007 #ifdef CONFIG_CRASH_CORE
1008 /*
1009  * This appends the listed symbols to /proc/vmcore
1010  *
1011  * /proc/vmcore is used by various utilities, like crash and makedumpfile to
1012  * obtain access to symbols that are otherwise very difficult to locate.  These
1013  * symbols are specifically used so that utilities can access and extract the
1014  * dmesg log from a vmcore file after a crash.
1015  */
1016 void log_buf_vmcoreinfo_setup(void)
1017 {
1018         VMCOREINFO_SYMBOL(log_buf);
1019         VMCOREINFO_SYMBOL(log_buf_len);
1020         VMCOREINFO_SYMBOL(log_first_idx);
1021         VMCOREINFO_SYMBOL(clear_idx);
1022         VMCOREINFO_SYMBOL(log_next_idx);
1023         /*
1024          * Export struct printk_log size and field offsets. User space tools can
1025          * parse it and detect any changes to structure down the line.
1026          */
1027         VMCOREINFO_STRUCT_SIZE(printk_log);
1028         VMCOREINFO_OFFSET(printk_log, ts_nsec);
1029         VMCOREINFO_OFFSET(printk_log, len);
1030         VMCOREINFO_OFFSET(printk_log, text_len);
1031         VMCOREINFO_OFFSET(printk_log, dict_len);
1032 }
1033 #endif
1034 
1035 /* requested log_buf_len from kernel cmdline */
1036 static unsigned long __initdata new_log_buf_len;
1037 
1038 /* we practice scaling the ring buffer by powers of 2 */
1039 static void __init log_buf_len_update(unsigned size)
1040 {
1041         if (size)
1042                 size = roundup_pow_of_two(size);
1043         if (size > log_buf_len)
1044                 new_log_buf_len = size;
1045 }
1046 
1047 /* save requested log_buf_len since it's too early to process it */
1048 static int __init log_buf_len_setup(char *str)
1049 {
1050         unsigned size = memparse(str, &str);
1051 
1052         log_buf_len_update(size);
1053 
1054         return 0;
1055 }
1056 early_param("log_buf_len", log_buf_len_setup);
1057 
1058 #ifdef CONFIG_SMP
1059 #define __LOG_CPU_MAX_BUF_LEN (1 << CONFIG_LOG_CPU_MAX_BUF_SHIFT)
1060 
1061 static void __init log_buf_add_cpu(void)
1062 {
1063         unsigned int cpu_extra;
1064 
1065         /*
1066          * archs should set up cpu_possible_bits properly with
1067          * set_cpu_possible() after setup_arch() but just in
1068          * case lets ensure this is valid.
1069          */
1070         if (num_possible_cpus() == 1)
1071                 return;
1072 
1073         cpu_extra = (num_possible_cpus() - 1) * __LOG_CPU_MAX_BUF_LEN;
1074 
1075         /* by default this will only continue through for large > 64 CPUs */
1076         if (cpu_extra <= __LOG_BUF_LEN / 2)
1077                 return;
1078 
1079         pr_info("log_buf_len individual max cpu contribution: %d bytes\n",
1080                 __LOG_CPU_MAX_BUF_LEN);
1081         pr_info("log_buf_len total cpu_extra contributions: %d bytes\n",
1082                 cpu_extra);
1083         pr_info("log_buf_len min size: %d bytes\n", __LOG_BUF_LEN);
1084 
1085         log_buf_len_update(cpu_extra + __LOG_BUF_LEN);
1086 }
1087 #else /* !CONFIG_SMP */
1088 static inline void log_buf_add_cpu(void) {}
1089 #endif /* CONFIG_SMP */
1090 
1091 void __init setup_log_buf(int early)
1092 {
1093         unsigned long flags;
1094         char *new_log_buf;
1095         int free;
1096 
1097         if (log_buf != __log_buf)
1098                 return;
1099 
1100         if (!early && !new_log_buf_len)
1101                 log_buf_add_cpu();
1102 
1103         if (!new_log_buf_len)
1104                 return;
1105 
1106         if (early) {
1107                 new_log_buf =
1108                         memblock_virt_alloc(new_log_buf_len, LOG_ALIGN);
1109         } else {
1110                 new_log_buf = memblock_virt_alloc_nopanic(new_log_buf_len,
1111                                                           LOG_ALIGN);
1112         }
1113 
1114         if (unlikely(!new_log_buf)) {
1115                 pr_err("log_buf_len: %ld bytes not available\n",
1116                         new_log_buf_len);
1117                 return;
1118         }
1119 
1120         logbuf_lock_irqsave(flags);
1121         log_buf_len = new_log_buf_len;
1122         log_buf = new_log_buf;
1123         new_log_buf_len = 0;
1124         free = __LOG_BUF_LEN - log_next_idx;
1125         memcpy(log_buf, __log_buf, __LOG_BUF_LEN);
1126         logbuf_unlock_irqrestore(flags);
1127 
1128         pr_info("log_buf_len: %d bytes\n", log_buf_len);
1129         pr_info("early log buf free: %d(%d%%)\n",
1130                 free, (free * 100) / __LOG_BUF_LEN);
1131 }
1132 
1133 static bool __read_mostly ignore_loglevel;
1134 
1135 static int __init ignore_loglevel_setup(char *str)
1136 {
1137         ignore_loglevel = true;
1138         pr_info("debug: ignoring loglevel setting.\n");
1139 
1140         return 0;
1141 }
1142 
1143 early_param("ignore_loglevel", ignore_loglevel_setup);
1144 module_param(ignore_loglevel, bool, S_IRUGO | S_IWUSR);
1145 MODULE_PARM_DESC(ignore_loglevel,
1146                  "ignore loglevel setting (prints all kernel messages to the console)");
1147 
1148 static bool suppress_message_printing(int level)
1149 {
1150         return (level >= console_loglevel && !ignore_loglevel);
1151 }
1152 
1153 #ifdef CONFIG_BOOT_PRINTK_DELAY
1154 
1155 static int boot_delay; /* msecs delay after each printk during bootup */
1156 static unsigned long long loops_per_msec;       /* based on boot_delay */
1157 
1158 static int __init boot_delay_setup(char *str)
1159 {
1160         unsigned long lpj;
1161 
1162         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
1163         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
1164 
1165         get_option(&str, &boot_delay);
1166         if (boot_delay > 10 * 1000)
1167                 boot_delay = 0;
1168 
1169         pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
1170                 "HZ: %d, loops_per_msec: %llu\n",
1171                 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
1172         return 0;
1173 }
1174 early_param("boot_delay", boot_delay_setup);
1175 
1176 static void boot_delay_msec(int level)
1177 {
1178         unsigned long long k;
1179         unsigned long timeout;
1180 
1181         if ((boot_delay == 0 || system_state >= SYSTEM_RUNNING)
1182                 || suppress_message_printing(level)) {
1183                 return;
1184         }
1185 
1186         k = (unsigned long long)loops_per_msec * boot_delay;
1187 
1188         timeout = jiffies + msecs_to_jiffies(boot_delay);
1189         while (k) {
1190                 k--;
1191                 cpu_relax();
1192                 /*
1193                  * use (volatile) jiffies to prevent
1194                  * compiler reduction; loop termination via jiffies
1195                  * is secondary and may or may not happen.
1196                  */
1197                 if (time_after(jiffies, timeout))
1198                         break;
1199                 touch_nmi_watchdog();
1200         }
1201 }
1202 #else
1203 static inline void boot_delay_msec(int level)
1204 {
1205 }
1206 #endif
1207 
1208 static bool printk_time = IS_ENABLED(CONFIG_PRINTK_TIME);
1209 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
1210 
1211 static size_t print_time(u64 ts, char *buf)
1212 {
1213         unsigned long rem_nsec;
1214 
1215         if (!printk_time)
1216                 return 0;
1217 
1218         rem_nsec = do_div(ts, 1000000000);
1219 
1220         if (!buf)
1221                 return snprintf(NULL, 0, "[%5lu.000000] ", (unsigned long)ts);
1222 
1223         return sprintf(buf, "[%5lu.%06lu] ",
1224                        (unsigned long)ts, rem_nsec / 1000);
1225 }
1226 
1227 static size_t print_prefix(const struct printk_log *msg, bool syslog, char *buf)
1228 {
1229         size_t len = 0;
1230         unsigned int prefix = (msg->facility << 3) | msg->level;
1231 
1232         if (syslog) {
1233                 if (buf) {
1234                         len += sprintf(buf, "<%u>", prefix);
1235                 } else {
1236                         len += 3;
1237                         if (prefix > 999)
1238                                 len += 3;
1239                         else if (prefix > 99)
1240                                 len += 2;
1241                         else if (prefix > 9)
1242                                 len++;
1243                 }
1244         }
1245 
1246         len += print_time(msg->ts_nsec, buf ? buf + len : NULL);
1247         return len;
1248 }
1249 
1250 static size_t msg_print_text(const struct printk_log *msg, bool syslog, char *buf, size_t size)
1251 {
1252         const char *text = log_text(msg);
1253         size_t text_size = msg->text_len;
1254         size_t len = 0;
1255 
1256         do {
1257                 const char *next = memchr(text, '\n', text_size);
1258                 size_t text_len;
1259 
1260                 if (next) {
1261                         text_len = next - text;
1262                         next++;
1263                         text_size -= next - text;
1264                 } else {
1265                         text_len = text_size;
1266                 }
1267 
1268                 if (buf) {
1269                         if (print_prefix(msg, syslog, NULL) +
1270                             text_len + 1 >= size - len)
1271                                 break;
1272 
1273                         len += print_prefix(msg, syslog, buf + len);
1274                         memcpy(buf + len, text, text_len);
1275                         len += text_len;
1276                         buf[len++] = '\n';
1277                 } else {
1278                         /* SYSLOG_ACTION_* buffer size only calculation */
1279                         len += print_prefix(msg, syslog, NULL);
1280                         len += text_len;
1281                         len++;
1282                 }
1283 
1284                 text = next;
1285         } while (text);
1286 
1287         return len;
1288 }
1289 
1290 static int syslog_print(char __user *buf, int size)
1291 {
1292         char *text;
1293         struct printk_log *msg;
1294         int len = 0;
1295 
1296         text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
1297         if (!text)
1298                 return -ENOMEM;
1299 
1300         while (size > 0) {
1301                 size_t n;
1302                 size_t skip;
1303 
1304                 logbuf_lock_irq();
1305                 if (syslog_seq < log_first_seq) {
1306                         /* messages are gone, move to first one */
1307                         syslog_seq = log_first_seq;
1308                         syslog_idx = log_first_idx;
1309                         syslog_partial = 0;
1310                 }
1311                 if (syslog_seq == log_next_seq) {
1312                         logbuf_unlock_irq();
1313                         break;
1314                 }
1315 
1316                 skip = syslog_partial;
1317                 msg = log_from_idx(syslog_idx);
1318                 n = msg_print_text(msg, true, text, LOG_LINE_MAX + PREFIX_MAX);
1319                 if (n - syslog_partial <= size) {
1320                         /* message fits into buffer, move forward */
1321                         syslog_idx = log_next(syslog_idx);
1322                         syslog_seq++;
1323                         n -= syslog_partial;
1324                         syslog_partial = 0;
1325                 } else if (!len){
1326                         /* partial read(), remember position */
1327                         n = size;
1328                         syslog_partial += n;
1329                 } else
1330                         n = 0;
1331                 logbuf_unlock_irq();
1332 
1333                 if (!n)
1334                         break;
1335 
1336                 if (copy_to_user(buf, text + skip, n)) {
1337                         if (!len)
1338                                 len = -EFAULT;
1339                         break;
1340                 }
1341 
1342                 len += n;
1343                 size -= n;
1344                 buf += n;
1345         }
1346 
1347         kfree(text);
1348         return len;
1349 }
1350 
1351 static int syslog_print_all(char __user *buf, int size, bool clear)
1352 {
1353         char *text;
1354         int len = 0;
1355 
1356         text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
1357         if (!text)
1358                 return -ENOMEM;
1359 
1360         logbuf_lock_irq();
1361         if (buf) {
1362                 u64 next_seq;
1363                 u64 seq;
1364                 u32 idx;
1365 
1366                 /*
1367                  * Find first record that fits, including all following records,
1368                  * into the user-provided buffer for this dump.
1369                  */
1370                 seq = clear_seq;
1371                 idx = clear_idx;
1372                 while (seq < log_next_seq) {
1373                         struct printk_log *msg = log_from_idx(idx);
1374 
1375                         len += msg_print_text(msg, true, NULL, 0);
1376                         idx = log_next(idx);
1377                         seq++;
1378                 }
1379 
1380                 /* move first record forward until length fits into the buffer */
1381                 seq = clear_seq;
1382                 idx = clear_idx;
1383                 while (len > size && seq < log_next_seq) {
1384                         struct printk_log *msg = log_from_idx(idx);
1385 
1386                         len -= msg_print_text(msg, true, NULL, 0);
1387                         idx = log_next(idx);
1388                         seq++;
1389                 }
1390 
1391                 /* last message fitting into this dump */
1392                 next_seq = log_next_seq;
1393 
1394                 len = 0;
1395                 while (len >= 0 && seq < next_seq) {
1396                         struct printk_log *msg = log_from_idx(idx);
1397                         int textlen;
1398 
1399                         textlen = msg_print_text(msg, true, text,
1400                                                  LOG_LINE_MAX + PREFIX_MAX);
1401                         if (textlen < 0) {
1402                                 len = textlen;
1403                                 break;
1404                         }
1405                         idx = log_next(idx);
1406                         seq++;
1407 
1408                         logbuf_unlock_irq();
1409                         if (copy_to_user(buf + len, text, textlen))
1410                                 len = -EFAULT;
1411                         else
1412                                 len += textlen;
1413                         logbuf_lock_irq();
1414 
1415                         if (seq < log_first_seq) {
1416                                 /* messages are gone, move to next one */
1417                                 seq = log_first_seq;
1418                                 idx = log_first_idx;
1419                         }
1420                 }
1421         }
1422 
1423         if (clear) {
1424                 clear_seq = log_next_seq;
1425                 clear_idx = log_next_idx;
1426         }
1427         logbuf_unlock_irq();
1428 
1429         kfree(text);
1430         return len;
1431 }
1432 
1433 int do_syslog(int type, char __user *buf, int len, int source)
1434 {
1435         bool clear = false;
1436         static int saved_console_loglevel = LOGLEVEL_DEFAULT;
1437         int error;
1438 
1439         error = check_syslog_permissions(type, source);
1440         if (error)
1441                 return error;
1442 
1443         switch (type) {
1444         case SYSLOG_ACTION_CLOSE:       /* Close log */
1445                 break;
1446         case SYSLOG_ACTION_OPEN:        /* Open log */
1447                 break;
1448         case SYSLOG_ACTION_READ:        /* Read from log */
1449                 if (!buf || len < 0)
1450                         return -EINVAL;
1451                 if (!len)
1452                         return 0;
1453                 if (!access_ok(VERIFY_WRITE, buf, len))
1454                         return -EFAULT;
1455                 error = wait_event_interruptible(log_wait,
1456                                                  syslog_seq != log_next_seq);
1457                 if (error)
1458                         return error;
1459                 error = syslog_print(buf, len);
1460                 break;
1461         /* Read/clear last kernel messages */
1462         case SYSLOG_ACTION_READ_CLEAR:
1463                 clear = true;
1464                 /* FALL THRU */
1465         /* Read last kernel messages */
1466         case SYSLOG_ACTION_READ_ALL:
1467                 if (!buf || len < 0)
1468                         return -EINVAL;
1469                 if (!len)
1470                         return 0;
1471                 if (!access_ok(VERIFY_WRITE, buf, len))
1472                         return -EFAULT;
1473                 error = syslog_print_all(buf, len, clear);
1474                 break;
1475         /* Clear ring buffer */
1476         case SYSLOG_ACTION_CLEAR:
1477                 syslog_print_all(NULL, 0, true);
1478                 break;
1479         /* Disable logging to console */
1480         case SYSLOG_ACTION_CONSOLE_OFF:
1481                 if (saved_console_loglevel == LOGLEVEL_DEFAULT)
1482                         saved_console_loglevel = console_loglevel;
1483                 console_loglevel = minimum_console_loglevel;
1484                 break;
1485         /* Enable logging to console */
1486         case SYSLOG_ACTION_CONSOLE_ON:
1487                 if (saved_console_loglevel != LOGLEVEL_DEFAULT) {
1488                         console_loglevel = saved_console_loglevel;
1489                         saved_console_loglevel = LOGLEVEL_DEFAULT;
1490                 }
1491                 break;
1492         /* Set level of messages printed to console */
1493         case SYSLOG_ACTION_CONSOLE_LEVEL:
1494                 if (len < 1 || len > 8)
1495                         return -EINVAL;
1496                 if (len < minimum_console_loglevel)
1497                         len = minimum_console_loglevel;
1498                 console_loglevel = len;
1499                 /* Implicitly re-enable logging to console */
1500                 saved_console_loglevel = LOGLEVEL_DEFAULT;
1501                 break;
1502         /* Number of chars in the log buffer */
1503         case SYSLOG_ACTION_SIZE_UNREAD:
1504                 logbuf_lock_irq();
1505                 if (syslog_seq < log_first_seq) {
1506                         /* messages are gone, move to first one */
1507                         syslog_seq = log_first_seq;
1508                         syslog_idx = log_first_idx;
1509                         syslog_partial = 0;
1510                 }
1511                 if (source == SYSLOG_FROM_PROC) {
1512                         /*
1513                          * Short-cut for poll(/"proc/kmsg") which simply checks
1514                          * for pending data, not the size; return the count of
1515                          * records, not the length.
1516                          */
1517                         error = log_next_seq - syslog_seq;
1518                 } else {
1519                         u64 seq = syslog_seq;
1520                         u32 idx = syslog_idx;
1521 
1522                         while (seq < log_next_seq) {
1523                                 struct printk_log *msg = log_from_idx(idx);
1524 
1525                                 error += msg_print_text(msg, true, NULL, 0);
1526                                 idx = log_next(idx);
1527                                 seq++;
1528                         }
1529                         error -= syslog_partial;
1530                 }
1531                 logbuf_unlock_irq();
1532                 break;
1533         /* Size of the log buffer */
1534         case SYSLOG_ACTION_SIZE_BUFFER:
1535                 error = log_buf_len;
1536                 break;
1537         default:
1538                 error = -EINVAL;
1539                 break;
1540         }
1541 
1542         return error;
1543 }
1544 
1545 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
1546 {
1547         return do_syslog(type, buf, len, SYSLOG_FROM_READER);
1548 }
1549 
1550 /*
1551  * Special console_lock variants that help to reduce the risk of soft-lockups.
1552  * They allow to pass console_lock to another printk() call using a busy wait.
1553  */
1554 
1555 #ifdef CONFIG_LOCKDEP
1556 static struct lockdep_map console_owner_dep_map = {
1557         .name = "console_owner"
1558 };
1559 #endif
1560 
1561 static DEFINE_RAW_SPINLOCK(console_owner_lock);
1562 static struct task_struct *console_owner;
1563 static bool console_waiter;
1564 
1565 /**
1566  * console_lock_spinning_enable - mark beginning of code where another
1567  *      thread might safely busy wait
1568  *
1569  * This basically converts console_lock into a spinlock. This marks
1570  * the section where the console_lock owner can not sleep, because
1571  * there may be a waiter spinning (like a spinlock). Also it must be
1572  * ready to hand over the lock at the end of the section.
1573  */
1574 static void console_lock_spinning_enable(void)
1575 {
1576         raw_spin_lock(&console_owner_lock);
1577         console_owner = current;
1578         raw_spin_unlock(&console_owner_lock);
1579 
1580         /* The waiter may spin on us after setting console_owner */
1581         spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
1582 }
1583 
1584 /**
1585  * console_lock_spinning_disable_and_check - mark end of code where another
1586  *      thread was able to busy wait and check if there is a waiter
1587  *
1588  * This is called at the end of the section where spinning is allowed.
1589  * It has two functions. First, it is a signal that it is no longer
1590  * safe to start busy waiting for the lock. Second, it checks if
1591  * there is a busy waiter and passes the lock rights to her.
1592  *
1593  * Important: Callers lose the lock if there was a busy waiter.
1594  *      They must not touch items synchronized by console_lock
1595  *      in this case.
1596  *
1597  * Return: 1 if the lock rights were passed, 0 otherwise.
1598  */
1599 static int console_lock_spinning_disable_and_check(void)
1600 {
1601         int waiter;
1602 
1603         raw_spin_lock(&console_owner_lock);
1604         waiter = READ_ONCE(console_waiter);
1605         console_owner = NULL;
1606         raw_spin_unlock(&console_owner_lock);
1607 
1608         if (!waiter) {
1609                 spin_release(&console_owner_dep_map, 1, _THIS_IP_);
1610                 return 0;
1611         }
1612 
1613         /* The waiter is now free to continue */
1614         WRITE_ONCE(console_waiter, false);
1615 
1616         spin_release(&console_owner_dep_map, 1, _THIS_IP_);
1617 
1618         /*
1619          * Hand off console_lock to waiter. The waiter will perform
1620          * the up(). After this, the waiter is the console_lock owner.
1621          */
1622         mutex_release(&console_lock_dep_map, 1, _THIS_IP_);
1623         return 1;
1624 }
1625 
1626 /**
1627  * console_trylock_spinning - try to get console_lock by busy waiting
1628  *
1629  * This allows to busy wait for the console_lock when the current
1630  * owner is running in specially marked sections. It means that
1631  * the current owner is running and cannot reschedule until it
1632  * is ready to lose the lock.
1633  *
1634  * Return: 1 if we got the lock, 0 othrewise
1635  */
1636 static int console_trylock_spinning(void)
1637 {
1638         struct task_struct *owner = NULL;
1639         bool waiter;
1640         bool spin = false;
1641         unsigned long flags;
1642 
1643         if (console_trylock())
1644                 return 1;
1645 
1646         printk_safe_enter_irqsave(flags);
1647 
1648         raw_spin_lock(&console_owner_lock);
1649         owner = READ_ONCE(console_owner);
1650         waiter = READ_ONCE(console_waiter);
1651         if (!waiter && owner && owner != current) {
1652                 WRITE_ONCE(console_waiter, true);
1653                 spin = true;
1654         }
1655         raw_spin_unlock(&console_owner_lock);
1656 
1657         /*
1658          * If there is an active printk() writing to the
1659          * consoles, instead of having it write our data too,
1660          * see if we can offload that load from the active
1661          * printer, and do some printing ourselves.
1662          * Go into a spin only if there isn't already a waiter
1663          * spinning, and there is an active printer, and
1664          * that active printer isn't us (recursive printk?).
1665          */
1666         if (!spin) {
1667                 printk_safe_exit_irqrestore(flags);
1668                 return 0;
1669         }
1670 
1671         /* We spin waiting for the owner to release us */
1672         spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
1673         /* Owner will clear console_waiter on hand off */
1674         while (READ_ONCE(console_waiter))
1675                 cpu_relax();
1676         spin_release(&console_owner_dep_map, 1, _THIS_IP_);
1677 
1678         printk_safe_exit_irqrestore(flags);
1679         /*
1680          * The owner passed the console lock to us.
1681          * Since we did not spin on console lock, annotate
1682          * this as a trylock. Otherwise lockdep will
1683          * complain.
1684          */
1685         mutex_acquire(&console_lock_dep_map, 0, 1, _THIS_IP_);
1686 
1687         return 1;
1688 }
1689 
1690 /*
1691  * Call the console drivers, asking them to write out
1692  * log_buf[start] to log_buf[end - 1].
1693  * The console_lock must be held.
1694  */
1695 static void call_console_drivers(const char *ext_text, size_t ext_len,
1696                                  const char *text, size_t len)
1697 {
1698         struct console *con;
1699 
1700         trace_console_rcuidle(text, len);
1701 
1702         if (!console_drivers)
1703                 return;
1704 
1705         for_each_console(con) {
1706                 if (exclusive_console && con != exclusive_console)
1707                         continue;
1708                 if (!(con->flags & CON_ENABLED))
1709                         continue;
1710                 if (!con->write)
1711                         continue;
1712                 if (!cpu_online(smp_processor_id()) &&
1713                     !(con->flags & CON_ANYTIME))
1714                         continue;
1715                 if (con->flags & CON_EXTENDED)
1716                         con->write(con, ext_text, ext_len);
1717                 else
1718                         con->write(con, text, len);
1719         }
1720 }
1721 
1722 int printk_delay_msec __read_mostly;
1723 
1724 static inline void printk_delay(void)
1725 {
1726         if (unlikely(printk_delay_msec)) {
1727                 int m = printk_delay_msec;
1728 
1729                 while (m--) {
1730                         mdelay(1);
1731                         touch_nmi_watchdog();
1732                 }
1733         }
1734 }
1735 
1736 /*
1737  * Continuation lines are buffered, and not committed to the record buffer
1738  * until the line is complete, or a race forces it. The line fragments
1739  * though, are printed immediately to the consoles to ensure everything has
1740  * reached the console in case of a kernel crash.
1741  */
1742 static struct cont {
1743         char buf[LOG_LINE_MAX];
1744         size_t len;                     /* length == 0 means unused buffer */
1745         struct task_struct *owner;      /* task of first print*/
1746         u64 ts_nsec;                    /* time of first print */
1747         u8 level;                       /* log level of first message */
1748         u8 facility;                    /* log facility of first message */
1749         enum log_flags flags;           /* prefix, newline flags */
1750 } cont;
1751 
1752 static void cont_flush(void)
1753 {
1754         if (cont.len == 0)
1755                 return;
1756 
1757         log_store(cont.facility, cont.level, cont.flags, cont.ts_nsec,
1758                   NULL, 0, cont.buf, cont.len);
1759         cont.len = 0;
1760 }
1761 
1762 static bool cont_add(int facility, int level, enum log_flags flags, const char *text, size_t len)
1763 {
1764         /*
1765          * If ext consoles are present, flush and skip in-kernel
1766          * continuation.  See nr_ext_console_drivers definition.  Also, if
1767          * the line gets too long, split it up in separate records.
1768          */
1769         if (nr_ext_console_drivers || cont.len + len > sizeof(cont.buf)) {
1770                 cont_flush();
1771                 return false;
1772         }
1773 
1774         if (!cont.len) {
1775                 cont.facility = facility;
1776                 cont.level = level;
1777                 cont.owner = current;
1778                 cont.ts_nsec = local_clock();
1779                 cont.flags = flags;
1780         }
1781 
1782         memcpy(cont.buf + cont.len, text, len);
1783         cont.len += len;
1784 
1785         // The original flags come from the first line,
1786         // but later continuations can add a newline.
1787         if (flags & LOG_NEWLINE) {
1788                 cont.flags |= LOG_NEWLINE;
1789                 cont_flush();
1790         }
1791 
1792         if (cont.len > (sizeof(cont.buf) * 80) / 100)
1793                 cont_flush();
1794 
1795         return true;
1796 }
1797 
1798 static size_t log_output(int facility, int level, enum log_flags lflags, const char *dict, size_t dictlen, char *text, size_t text_len)
1799 {
1800         /*
1801          * If an earlier line was buffered, and we're a continuation
1802          * write from the same process, try to add it to the buffer.
1803          */
1804         if (cont.len) {
1805                 if (cont.owner == current && (lflags & LOG_CONT)) {
1806                         if (cont_add(facility, level, lflags, text, text_len))
1807                                 return text_len;
1808                 }
1809                 /* Otherwise, make sure it's flushed */
1810                 cont_flush();
1811         }
1812 
1813         /* Skip empty continuation lines that couldn't be added - they just flush */
1814         if (!text_len && (lflags & LOG_CONT))
1815                 return 0;
1816 
1817         /* If it doesn't end in a newline, try to buffer the current line */
1818         if (!(lflags & LOG_NEWLINE)) {
1819                 if (cont_add(facility, level, lflags, text, text_len))
1820                         return text_len;
1821         }
1822 
1823         /* Store it in the record log */
1824         return log_store(facility, level, lflags, 0, dict, dictlen, text, text_len);
1825 }
1826 
1827 asmlinkage int vprintk_emit(int facility, int level,
1828                             const char *dict, size_t dictlen,
1829                             const char *fmt, va_list args)
1830 {
1831         static char textbuf[LOG_LINE_MAX];
1832         char *text = textbuf;
1833         size_t text_len;
1834         enum log_flags lflags = 0;
1835         unsigned long flags;
1836         int printed_len;
1837         bool in_sched = false;
1838 
1839         if (level == LOGLEVEL_SCHED) {
1840                 level = LOGLEVEL_DEFAULT;
1841                 in_sched = true;
1842         }
1843 
1844         boot_delay_msec(level);
1845         printk_delay();
1846 
1847         /* This stops the holder of console_sem just where we want him */
1848         logbuf_lock_irqsave(flags);
1849         /*
1850          * The printf needs to come first; we need the syslog
1851          * prefix which might be passed-in as a parameter.
1852          */
1853         text_len = vscnprintf(text, sizeof(textbuf), fmt, args);
1854 
1855         /* mark and strip a trailing newline */
1856         if (text_len && text[text_len-1] == '\n') {
1857                 text_len--;
1858                 lflags |= LOG_NEWLINE;
1859         }
1860 
1861         /* strip kernel syslog prefix and extract log level or control flags */
1862         if (facility == 0) {
1863                 int kern_level;
1864 
1865                 while ((kern_level = printk_get_level(text)) != 0) {
1866                         switch (kern_level) {
1867                         case '' ... '7':
1868                                 if (level == LOGLEVEL_DEFAULT)
1869                                         level = kern_level - '';
1870                                 /* fallthrough */
1871                         case 'd':       /* KERN_DEFAULT */
1872                                 lflags |= LOG_PREFIX;
1873                                 break;
1874                         case 'c':       /* KERN_CONT */
1875                                 lflags |= LOG_CONT;
1876                         }
1877 
1878                         text_len -= 2;
1879                         text += 2;
1880                 }
1881         }
1882 
1883         if (level == LOGLEVEL_DEFAULT)
1884                 level = default_message_loglevel;
1885 
1886         if (dict)
1887                 lflags |= LOG_PREFIX|LOG_NEWLINE;
1888 
1889         printed_len = log_output(facility, level, lflags, dict, dictlen, text, text_len);
1890 
1891         logbuf_unlock_irqrestore(flags);
1892 
1893         /* If called from the scheduler, we can not call up(). */
1894         if (!in_sched) {
1895                 /*
1896                  * Disable preemption to avoid being preempted while holding
1897                  * console_sem which would prevent anyone from printing to
1898                  * console
1899                  */
1900                 preempt_disable();
1901                 /*
1902                  * Try to acquire and then immediately release the console
1903                  * semaphore.  The release will print out buffers and wake up
1904                  * /dev/kmsg and syslog() users.
1905                  */
1906                 if (console_trylock_spinning())
1907                         console_unlock();
1908                 preempt_enable();
1909         }
1910 
1911         return printed_len;
1912 }
1913 EXPORT_SYMBOL(vprintk_emit);
1914 
1915 asmlinkage int vprintk(const char *fmt, va_list args)
1916 {
1917         return vprintk_func(fmt, args);
1918 }
1919 EXPORT_SYMBOL(vprintk);
1920 
1921 asmlinkage int printk_emit(int facility, int level,
1922                            const char *dict, size_t dictlen,
1923                            const char *fmt, ...)
1924 {
1925         va_list args;
1926         int r;
1927 
1928         va_start(args, fmt);
1929         r = vprintk_emit(facility, level, dict, dictlen, fmt, args);
1930         va_end(args);
1931 
1932         return r;
1933 }
1934 EXPORT_SYMBOL(printk_emit);
1935 
1936 int vprintk_default(const char *fmt, va_list args)
1937 {
1938         int r;
1939 
1940 #ifdef CONFIG_KGDB_KDB
1941         /* Allow to pass printk() to kdb but avoid a recursion. */
1942         if (unlikely(kdb_trap_printk && kdb_printf_cpu < 0)) {
1943                 r = vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
1944                 return r;
1945         }
1946 #endif
1947         r = vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
1948 
1949         return r;
1950 }
1951 EXPORT_SYMBOL_GPL(vprintk_default);
1952 
1953 /**
1954  * printk - print a kernel message
1955  * @fmt: format string
1956  *
1957  * This is printk(). It can be called from any context. We want it to work.
1958  *
1959  * We try to grab the console_lock. If we succeed, it's easy - we log the
1960  * output and call the console drivers.  If we fail to get the semaphore, we
1961  * place the output into the log buffer and return. The current holder of
1962  * the console_sem will notice the new output in console_unlock(); and will
1963  * send it to the consoles before releasing the lock.
1964  *
1965  * One effect of this deferred printing is that code which calls printk() and
1966  * then changes console_loglevel may break. This is because console_loglevel
1967  * is inspected when the actual printing occurs.
1968  *
1969  * See also:
1970  * printf(3)
1971  *
1972  * See the vsnprintf() documentation for format string extensions over C99.
1973  */
1974 asmlinkage __visible int printk(const char *fmt, ...)
1975 {
1976         va_list args;
1977         int r;
1978 
1979         va_start(args, fmt);
1980         r = vprintk_func(fmt, args);
1981         va_end(args);
1982 
1983         return r;
1984 }
1985 EXPORT_SYMBOL(printk);
1986 
1987 #else /* CONFIG_PRINTK */
1988 
1989 #define LOG_LINE_MAX            0
1990 #define PREFIX_MAX              0
1991 
1992 static u64 syslog_seq;
1993 static u32 syslog_idx;
1994 static u64 console_seq;
1995 static u32 console_idx;
1996 static u64 log_first_seq;
1997 static u32 log_first_idx;
1998 static u64 log_next_seq;
1999 static char *log_text(const struct printk_log *msg) { return NULL; }
2000 static char *log_dict(const struct printk_log *msg) { return NULL; }
2001 static struct printk_log *log_from_idx(u32 idx) { return NULL; }
2002 static u32 log_next(u32 idx) { return 0; }
2003 static ssize_t msg_print_ext_header(char *buf, size_t size,
2004                                     struct printk_log *msg,
2005                                     u64 seq) { return 0; }
2006 static ssize_t msg_print_ext_body(char *buf, size_t size,
2007                                   char *dict, size_t dict_len,
2008                                   char *text, size_t text_len) { return 0; }
2009 static void console_lock_spinning_enable(void) { }
2010 static int console_lock_spinning_disable_and_check(void) { return 0; }
2011 static void call_console_drivers(const char *ext_text, size_t ext_len,
2012                                  const char *text, size_t len) {}
2013 static size_t msg_print_text(const struct printk_log *msg,
2014                              bool syslog, char *buf, size_t size) { return 0; }
2015 static bool suppress_message_printing(int level) { return false; }
2016 
2017 #endif /* CONFIG_PRINTK */
2018 
2019 #ifdef CONFIG_EARLY_PRINTK
2020 struct console *early_console;
2021 
2022 asmlinkage __visible void early_printk(const char *fmt, ...)
2023 {
2024         va_list ap;
2025         char buf[512];
2026         int n;
2027 
2028         if (!early_console)
2029                 return;
2030 
2031         va_start(ap, fmt);
2032         n = vscnprintf(buf, sizeof(buf), fmt, ap);
2033         va_end(ap);
2034 
2035         early_console->write(early_console, buf, n);
2036 }
2037 #endif
2038 
2039 static int __add_preferred_console(char *name, int idx, char *options,
2040                                    char *brl_options)
2041 {
2042         struct console_cmdline *c;
2043         int i;
2044 
2045         /*
2046          *      See if this tty is not yet registered, and
2047          *      if we have a slot free.
2048          */
2049         for (i = 0, c = console_cmdline;
2050              i < MAX_CMDLINECONSOLES && c->name[0];
2051              i++, c++) {
2052                 if (strcmp(c->name, name) == 0 && c->index == idx) {
2053                         if (!brl_options)
2054                                 preferred_console = i;
2055                         return 0;
2056                 }
2057         }
2058         if (i == MAX_CMDLINECONSOLES)
2059                 return -E2BIG;
2060         if (!brl_options)
2061                 preferred_console = i;
2062         strlcpy(c->name, name, sizeof(c->name));
2063         c->options = options;
2064         braille_set_options(c, brl_options);
2065 
2066         c->index = idx;
2067         return 0;
2068 }
2069 
2070 static int __init console_msg_format_setup(char *str)
2071 {
2072         if (!strcmp(str, "syslog"))
2073                 console_msg_format = MSG_FORMAT_SYSLOG;
2074         if (!strcmp(str, "default"))
2075                 console_msg_format = MSG_FORMAT_DEFAULT;
2076         return 1;
2077 }
2078 __setup("console_msg_format=", console_msg_format_setup);
2079 
2080 /*
2081  * Set up a console.  Called via do_early_param() in init/main.c
2082  * for each "console=" parameter in the boot command line.
2083  */
2084 static int __init console_setup(char *str)
2085 {
2086         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for "ttyS" */
2087         char *s, *options, *brl_options = NULL;
2088         int idx;
2089 
2090         if (_braille_console_setup(&str, &brl_options))
2091                 return 1;
2092 
2093         /*
2094          * Decode str into name, index, options.
2095          */
2096         if (str[0] >= '' && str[0] <= '9') {
2097                 strcpy(buf, "ttyS");
2098                 strncpy(buf + 4, str, sizeof(buf) - 5);
2099         } else {
2100                 strncpy(buf, str, sizeof(buf) - 1);
2101         }
2102         buf[sizeof(buf) - 1] = 0;
2103         options = strchr(str, ',');
2104         if (options)
2105                 *(options++) = 0;
2106 #ifdef __sparc__
2107         if (!strcmp(str, "ttya"))
2108                 strcpy(buf, "ttyS0");
2109         if (!strcmp(str, "ttyb"))
2110                 strcpy(buf, "ttyS1");
2111 #endif
2112         for (s = buf; *s; s++)
2113                 if (isdigit(*s) || *s == ',')
2114                         break;
2115         idx = simple_strtoul(s, NULL, 10);
2116         *s = 0;
2117 
2118         __add_preferred_console(buf, idx, options, brl_options);
2119         console_set_on_cmdline = 1;
2120         return 1;
2121 }
2122 __setup("console=", console_setup);
2123 
2124 /**
2125  * add_preferred_console - add a device to the list of preferred consoles.
2126  * @name: device name
2127  * @idx: device index
2128  * @options: options for this console
2129  *
2130  * The last preferred console added will be used for kernel messages
2131  * and stdin/out/err for init.  Normally this is used by console_setup
2132  * above to handle user-supplied console arguments; however it can also
2133  * be used by arch-specific code either to override the user or more
2134  * commonly to provide a default console (ie from PROM variables) when
2135  * the user has not supplied one.
2136  */
2137 int add_preferred_console(char *name, int idx, char *options)
2138 {
2139         return __add_preferred_console(name, idx, options, NULL);
2140 }
2141 
2142 bool console_suspend_enabled = true;
2143 EXPORT_SYMBOL(console_suspend_enabled);
2144 
2145 static int __init console_suspend_disable(char *str)
2146 {
2147         console_suspend_enabled = false;
2148         return 1;
2149 }
2150 __setup("no_console_suspend", console_suspend_disable);
2151 module_param_named(console_suspend, console_suspend_enabled,
2152                 bool, S_IRUGO | S_IWUSR);
2153 MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
2154         " and hibernate operations");
2155 
2156 /**
2157  * suspend_console - suspend the console subsystem
2158  *
2159  * This disables printk() while we go into suspend states
2160  */
2161 void suspend_console(void)
2162 {
2163         if (!console_suspend_enabled)
2164                 return;
2165         printk("Suspending console(s) (use no_console_suspend to debug)\n");
2166         console_lock();
2167         console_suspended = 1;
2168         up_console_sem();
2169 }
2170 
2171 void resume_console(void)
2172 {
2173         if (!console_suspend_enabled)
2174                 return;
2175         down_console_sem();
2176         console_suspended = 0;
2177         console_unlock();
2178 }
2179 
2180 /**
2181  * console_cpu_notify - print deferred console messages after CPU hotplug
2182  * @cpu: unused
2183  *
2184  * If printk() is called from a CPU that is not online yet, the messages
2185  * will be printed on the console only if there are CON_ANYTIME consoles.
2186  * This function is called when a new CPU comes online (or fails to come
2187  * up) or goes offline.
2188  */
2189 static int console_cpu_notify(unsigned int cpu)
2190 {
2191         if (!cpuhp_tasks_frozen) {
2192                 /* If trylock fails, someone else is doing the printing */
2193                 if (console_trylock())
2194                         console_unlock();
2195         }
2196         return 0;
2197 }
2198 
2199 /**
2200  * console_lock - lock the console system for exclusive use.
2201  *
2202  * Acquires a lock which guarantees that the caller has
2203  * exclusive access to the console system and the console_drivers list.
2204  *
2205  * Can sleep, returns nothing.
2206  */
2207 void console_lock(void)
2208 {
2209         might_sleep();
2210 
2211         down_console_sem();
2212         if (console_suspended)
2213                 return;
2214         console_locked = 1;
2215         console_may_schedule = 1;
2216 }
2217 EXPORT_SYMBOL(console_lock);
2218 
2219 /**
2220  * console_trylock - try to lock the console system for exclusive use.
2221  *
2222  * Try to acquire a lock which guarantees that the caller has exclusive
2223  * access to the console system and the console_drivers list.
2224  *
2225  * returns 1 on success, and 0 on failure to acquire the lock.
2226  */
2227 int console_trylock(void)
2228 {
2229         if (down_trylock_console_sem())
2230                 return 0;
2231         if (console_suspended) {
2232                 up_console_sem();
2233                 return 0;
2234         }
2235         console_locked = 1;
2236         console_may_schedule = 0;
2237         return 1;
2238 }
2239 EXPORT_SYMBOL(console_trylock);
2240 
2241 int is_console_locked(void)
2242 {
2243         return console_locked;
2244 }
2245 
2246 /*
2247  * Check if we have any console that is capable of printing while cpu is
2248  * booting or shutting down. Requires console_sem.
2249  */
2250 static int have_callable_console(void)
2251 {
2252         struct console *con;
2253 
2254         for_each_console(con)
2255                 if ((con->flags & CON_ENABLED) &&
2256                                 (con->flags & CON_ANYTIME))
2257                         return 1;
2258 
2259         return 0;
2260 }
2261 
2262 /*
2263  * Can we actually use the console at this time on this cpu?
2264  *
2265  * Console drivers may assume that per-cpu resources have been allocated. So
2266  * unless they're explicitly marked as being able to cope (CON_ANYTIME) don't
2267  * call them until this CPU is officially up.
2268  */
2269 static inline int can_use_console(void)
2270 {
2271         return cpu_online(raw_smp_processor_id()) || have_callable_console();
2272 }
2273 
2274 /**
2275  * console_unlock - unlock the console system
2276  *
2277  * Releases the console_lock which the caller holds on the console system
2278  * and the console driver list.
2279  *
2280  * While the console_lock was held, console output may have been buffered
2281  * by printk().  If this is the case, console_unlock(); emits
2282  * the output prior to releasing the lock.
2283  *
2284  * If there is output waiting, we wake /dev/kmsg and syslog() users.
2285  *
2286  * console_unlock(); may be called from any context.
2287  */
2288 void console_unlock(void)
2289 {
2290         static char ext_text[CONSOLE_EXT_LOG_MAX];
2291         static char text[LOG_LINE_MAX + PREFIX_MAX];
2292         static u64 seen_seq;
2293         unsigned long flags;
2294         bool wake_klogd = false;
2295         bool do_cond_resched, retry;
2296 
2297         if (console_suspended) {
2298                 up_console_sem();
2299                 return;
2300         }
2301 
2302         /*
2303          * Console drivers are called with interrupts disabled, so
2304          * @console_may_schedule should be cleared before; however, we may
2305          * end up dumping a lot of lines, for example, if called from
2306          * console registration path, and should invoke cond_resched()
2307          * between lines if allowable.  Not doing so can cause a very long
2308          * scheduling stall on a slow console leading to RCU stall and
2309          * softlockup warnings which exacerbate the issue with more
2310          * messages practically incapacitating the system.
2311          *
2312          * console_trylock() is not able to detect the preemptive
2313          * context reliably. Therefore the value must be stored before
2314          * and cleared after the the "again" goto label.
2315          */
2316         do_cond_resched = console_may_schedule;
2317 again:
2318         console_may_schedule = 0;
2319 
2320         /*
2321          * We released the console_sem lock, so we need to recheck if
2322          * cpu is online and (if not) is there at least one CON_ANYTIME
2323          * console.
2324          */
2325         if (!can_use_console()) {
2326                 console_locked = 0;
2327                 up_console_sem();
2328                 return;
2329         }
2330 
2331         for (;;) {
2332                 struct printk_log *msg;
2333                 size_t ext_len = 0;
2334                 size_t len;
2335 
2336                 printk_safe_enter_irqsave(flags);
2337                 raw_spin_lock(&logbuf_lock);
2338                 if (seen_seq != log_next_seq) {
2339                         wake_klogd = true;
2340                         seen_seq = log_next_seq;
2341                 }
2342 
2343                 if (console_seq < log_first_seq) {
2344                         len = sprintf(text, "** %u printk messages dropped **\n",
2345                                       (unsigned)(log_first_seq - console_seq));
2346 
2347                         /* messages are gone, move to first one */
2348                         console_seq = log_first_seq;
2349                         console_idx = log_first_idx;
2350                 } else {
2351                         len = 0;
2352                 }
2353 skip:
2354                 if (console_seq == log_next_seq)
2355                         break;
2356 
2357                 msg = log_from_idx(console_idx);
2358                 if (suppress_message_printing(msg->level)) {
2359                         /*
2360                          * Skip record we have buffered and already printed
2361                          * directly to the console when we received it, and
2362                          * record that has level above the console loglevel.
2363                          */
2364                         console_idx = log_next(console_idx);
2365                         console_seq++;
2366                         goto skip;
2367                 }
2368 
2369                 len += msg_print_text(msg,
2370                                 console_msg_format & MSG_FORMAT_SYSLOG,
2371                                 text + len,
2372                                 sizeof(text) - len);
2373                 if (nr_ext_console_drivers) {
2374                         ext_len = msg_print_ext_header(ext_text,
2375                                                 sizeof(ext_text),
2376                                                 msg, console_seq);
2377                         ext_len += msg_print_ext_body(ext_text + ext_len,
2378                                                 sizeof(ext_text) - ext_len,
2379                                                 log_dict(msg), msg->dict_len,
2380                                                 log_text(msg), msg->text_len);
2381                 }
2382                 console_idx = log_next(console_idx);
2383                 console_seq++;
2384                 raw_spin_unlock(&logbuf_lock);
2385 
2386                 /*
2387                  * While actively printing out messages, if another printk()
2388                  * were to occur on another CPU, it may wait for this one to
2389                  * finish. This task can not be preempted if there is a
2390                  * waiter waiting to take over.
2391                  */
2392                 console_lock_spinning_enable();
2393 
2394                 stop_critical_timings();        /* don't trace print latency */
2395                 call_console_drivers(ext_text, ext_len, text, len);
2396                 start_critical_timings();
2397 
2398                 if (console_lock_spinning_disable_and_check()) {
2399                         printk_safe_exit_irqrestore(flags);
2400                         return;
2401                 }
2402 
2403                 printk_safe_exit_irqrestore(flags);
2404 
2405                 if (do_cond_resched)
2406                         cond_resched();
2407         }
2408 
2409         console_locked = 0;
2410 
2411         /* Release the exclusive_console once it is used */
2412         if (unlikely(exclusive_console))
2413                 exclusive_console = NULL;
2414 
2415         raw_spin_unlock(&logbuf_lock);
2416 
2417         up_console_sem();
2418 
2419         /*
2420          * Someone could have filled up the buffer again, so re-check if there's
2421          * something to flush. In case we cannot trylock the console_sem again,
2422          * there's a new owner and the console_unlock() from them will do the
2423          * flush, no worries.
2424          */
2425         raw_spin_lock(&logbuf_lock);
2426         retry = console_seq != log_next_seq;
2427         raw_spin_unlock(&logbuf_lock);
2428         printk_safe_exit_irqrestore(flags);
2429 
2430         if (retry && console_trylock())
2431                 goto again;
2432 
2433         if (wake_klogd)
2434                 wake_up_klogd();
2435 }
2436 EXPORT_SYMBOL(console_unlock);
2437 
2438 /**
2439  * console_conditional_schedule - yield the CPU if required
2440  *
2441  * If the console code is currently allowed to sleep, and
2442  * if this CPU should yield the CPU to another task, do
2443  * so here.
2444  *
2445  * Must be called within console_lock();.
2446  */
2447 void __sched console_conditional_schedule(void)
2448 {
2449         if (console_may_schedule)
2450                 cond_resched();
2451 }
2452 EXPORT_SYMBOL(console_conditional_schedule);
2453 
2454 void console_unblank(void)
2455 {
2456         struct console *c;
2457 
2458         /*
2459          * console_unblank can no longer be called in interrupt context unless
2460          * oops_in_progress is set to 1..
2461          */
2462         if (oops_in_progress) {
2463                 if (down_trylock_console_sem() != 0)
2464                         return;
2465         } else
2466                 console_lock();
2467 
2468         console_locked = 1;
2469         console_may_schedule = 0;
2470         for_each_console(c)
2471                 if ((c->flags & CON_ENABLED) && c->unblank)
2472                         c->unblank();
2473         console_unlock();
2474 }
2475 
2476 /**
2477  * console_flush_on_panic - flush console content on panic
2478  *
2479  * Immediately output all pending messages no matter what.
2480  */
2481 void console_flush_on_panic(void)
2482 {
2483         /*
2484          * If someone else is holding the console lock, trylock will fail
2485          * and may_schedule may be set.  Ignore and proceed to unlock so
2486          * that messages are flushed out.  As this can be called from any
2487          * context and we don't want to get preempted while flushing,
2488          * ensure may_schedule is cleared.
2489          */
2490         console_trylock();
2491         console_may_schedule = 0;
2492         console_unlock();
2493 }
2494 
2495 /*
2496  * Return the console tty driver structure and its associated index
2497  */
2498 struct tty_driver *console_device(int *index)
2499 {
2500         struct console *c;
2501         struct tty_driver *driver = NULL;
2502 
2503         console_lock();
2504         for_each_console(c) {
2505                 if (!c->device)
2506                         continue;
2507                 driver = c->device(c, index);
2508                 if (driver)
2509                         break;
2510         }
2511         console_unlock();
2512         return driver;
2513 }
2514 
2515 /*
2516  * Prevent further output on the passed console device so that (for example)
2517  * serial drivers can disable console output before suspending a port, and can
2518  * re-enable output afterwards.
2519  */
2520 void console_stop(struct console *console)
2521 {
2522         console_lock();
2523         console->flags &= ~CON_ENABLED;
2524         console_unlock();
2525 }
2526 EXPORT_SYMBOL(console_stop);
2527 
2528 void console_start(struct console *console)
2529 {
2530         console_lock();
2531         console->flags |= CON_ENABLED;
2532         console_unlock();
2533 }
2534 EXPORT_SYMBOL(console_start);
2535 
2536 static int __read_mostly keep_bootcon;
2537 
2538 static int __init keep_bootcon_setup(char *str)
2539 {
2540         keep_bootcon = 1;
2541         pr_info("debug: skip boot console de-registration.\n");
2542 
2543         return 0;
2544 }
2545 
2546 early_param("keep_bootcon", keep_bootcon_setup);
2547 
2548 /*
2549  * The console driver calls this routine during kernel initialization
2550  * to register the console printing procedure with printk() and to
2551  * print any messages that were printed by the kernel before the
2552  * console driver was initialized.
2553  *
2554  * This can happen pretty early during the boot process (because of
2555  * early_printk) - sometimes before setup_arch() completes - be careful
2556  * of what kernel features are used - they may not be initialised yet.
2557  *
2558  * There are two types of consoles - bootconsoles (early_printk) and
2559  * "real" consoles (everything which is not a bootconsole) which are
2560  * handled differently.
2561  *  - Any number of bootconsoles can be registered at any time.
2562  *  - As soon as a "real" console is registered, all bootconsoles
2563  *    will be unregistered automatically.
2564  *  - Once a "real" console is registered, any attempt to register a
2565  *    bootconsoles will be rejected
2566  */
2567 void register_console(struct console *newcon)
2568 {
2569         int i;
2570         unsigned long flags;
2571         struct console *bcon = NULL;
2572         struct console_cmdline *c;
2573         static bool has_preferred;
2574 
2575         if (console_drivers)
2576                 for_each_console(bcon)
2577                         if (WARN(bcon == newcon,
2578                                         "console '%s%d' already registered\n",
2579                                         bcon->name, bcon->index))
2580                                 return;
2581 
2582         /*
2583          * before we register a new CON_BOOT console, make sure we don't
2584          * already have a valid console
2585          */
2586         if (console_drivers && newcon->flags & CON_BOOT) {
2587                 /* find the last or real console */
2588                 for_each_console(bcon) {
2589                         if (!(bcon->flags & CON_BOOT)) {
2590                                 pr_info("Too late to register bootconsole %s%d\n",
2591                                         newcon->name, newcon->index);
2592                                 return;
2593                         }
2594                 }
2595         }
2596 
2597         if (console_drivers && console_drivers->flags & CON_BOOT)
2598                 bcon = console_drivers;
2599 
2600         if (!has_preferred || bcon || !console_drivers)
2601                 has_preferred = preferred_console >= 0;
2602 
2603         /*
2604          *      See if we want to use this console driver. If we
2605          *      didn't select a console we take the first one
2606          *      that registers here.
2607          */
2608         if (!has_preferred) {
2609                 if (newcon->index < 0)
2610                         newcon->index = 0;
2611                 if (newcon->setup == NULL ||
2612                     newcon->setup(newcon, NULL) == 0) {
2613                         newcon->flags |= CON_ENABLED;
2614                         if (newcon->device) {
2615                                 newcon->flags |= CON_CONSDEV;
2616                                 has_preferred = true;
2617                         }
2618                 }
2619         }
2620 
2621         /*
2622          *      See if this console matches one we selected on
2623          *      the command line.
2624          */
2625         for (i = 0, c = console_cmdline;
2626              i < MAX_CMDLINECONSOLES && c->name[0];
2627              i++, c++) {
2628                 if (!newcon->match ||
2629                     newcon->match(newcon, c->name, c->index, c->options) != 0) {
2630                         /* default matching */
2631                         BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));
2632                         if (strcmp(c->name, newcon->name) != 0)
2633                                 continue;
2634                         if (newcon->index >= 0 &&
2635                             newcon->index != c->index)
2636                                 continue;
2637                         if (newcon->index < 0)
2638                                 newcon->index = c->index;
2639 
2640                         if (_braille_register_console(newcon, c))
2641                                 return;
2642 
2643                         if (newcon->setup &&
2644                             newcon->setup(newcon, c->options) != 0)
2645                                 break;
2646                 }
2647 
2648                 newcon->flags |= CON_ENABLED;
2649                 if (i == preferred_console) {
2650                         newcon->flags |= CON_CONSDEV;
2651                         has_preferred = true;
2652                 }
2653                 break;
2654         }
2655 
2656         if (!(newcon->flags & CON_ENABLED))
2657                 return;
2658 
2659         /*
2660          * If we have a bootconsole, and are switching to a real console,
2661          * don't print everything out again, since when the boot console, and
2662          * the real console are the same physical device, it's annoying to
2663          * see the beginning boot messages twice
2664          */
2665         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
2666                 newcon->flags &= ~CON_PRINTBUFFER;
2667 
2668         /*
2669          *      Put this console in the list - keep the
2670          *      preferred driver at the head of the list.
2671          */
2672         console_lock();
2673         if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
2674                 newcon->next = console_drivers;
2675                 console_drivers = newcon;
2676                 if (newcon->next)
2677                         newcon->next->flags &= ~CON_CONSDEV;
2678         } else {
2679                 newcon->next = console_drivers->next;
2680                 console_drivers->next = newcon;
2681         }
2682 
2683         if (newcon->flags & CON_EXTENDED)
2684                 if (!nr_ext_console_drivers++)
2685                         pr_info("printk: continuation disabled due to ext consoles, expect more fragments in /dev/kmsg\n");
2686 
2687         if (newcon->flags & CON_PRINTBUFFER) {
2688                 /*
2689                  * console_unlock(); will print out the buffered messages
2690                  * for us.
2691                  */
2692                 logbuf_lock_irqsave(flags);
2693                 console_seq = syslog_seq;
2694                 console_idx = syslog_idx;
2695                 logbuf_unlock_irqrestore(flags);
2696                 /*
2697                  * We're about to replay the log buffer.  Only do this to the
2698                  * just-registered console to avoid excessive message spam to
2699                  * the already-registered consoles.
2700                  */
2701                 exclusive_console = newcon;
2702         }
2703         console_unlock();
2704         console_sysfs_notify();
2705 
2706         /*
2707          * By unregistering the bootconsoles after we enable the real console
2708          * we get the "console xxx enabled" message on all the consoles -
2709          * boot consoles, real consoles, etc - this is to ensure that end
2710          * users know there might be something in the kernel's log buffer that
2711          * went to the bootconsole (that they do not see on the real console)
2712          */
2713         pr_info("%sconsole [%s%d] enabled\n",
2714                 (newcon->flags & CON_BOOT) ? "boot" : "" ,
2715                 newcon->name, newcon->index);
2716         if (bcon &&
2717             ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) &&
2718             !keep_bootcon) {
2719                 /* We need to iterate through all boot consoles, to make
2720                  * sure we print everything out, before we unregister them.
2721                  */
2722                 for_each_console(bcon)
2723                         if (bcon->flags & CON_BOOT)
2724                                 unregister_console(bcon);
2725         }
2726 }
2727 EXPORT_SYMBOL(register_console);
2728 
2729 int unregister_console(struct console *console)
2730 {
2731         struct console *a, *b;
2732         int res;
2733 
2734         pr_info("%sconsole [%s%d] disabled\n",
2735                 (console->flags & CON_BOOT) ? "boot" : "" ,
2736                 console->name, console->index);
2737 
2738         res = _braille_unregister_console(console);
2739         if (res)
2740                 return res;
2741 
2742         res = 1;
2743         console_lock();
2744         if (console_drivers == console) {
2745                 console_drivers=console->next;
2746                 res = 0;
2747         } else if (console_drivers) {
2748                 for (a=console_drivers->next, b=console_drivers ;
2749                      a; b=a, a=b->next) {
2750                         if (a == console) {
2751                                 b->next = a->next;
2752                                 res = 0;
2753                                 break;
2754                         }
2755                 }
2756         }
2757 
2758         if (!res && (console->flags & CON_EXTENDED))
2759                 nr_ext_console_drivers--;
2760 
2761         /*
2762          * If this isn't the last console and it has CON_CONSDEV set, we
2763          * need to set it on the next preferred console.
2764          */
2765         if (console_drivers != NULL && console->flags & CON_CONSDEV)
2766                 console_drivers->flags |= CON_CONSDEV;
2767 
2768         console->flags &= ~CON_ENABLED;
2769         console_unlock();
2770         console_sysfs_notify();
2771         return res;
2772 }
2773 EXPORT_SYMBOL(unregister_console);
2774 
2775 /*
2776  * Initialize the console device. This is called *early*, so
2777  * we can't necessarily depend on lots of kernel help here.
2778  * Just do some early initializations, and do the complex setup
2779  * later.
2780  */
2781 void __init console_init(void)
2782 {
2783         initcall_t *call;
2784 
2785         /* Setup the default TTY line discipline. */
2786         n_tty_init();
2787 
2788         /*
2789          * set up the console device so that later boot sequences can
2790          * inform about problems etc..
2791          */
2792         call = __con_initcall_start;
2793         while (call < __con_initcall_end) {
2794                 (*call)();
2795                 call++;
2796         }
2797 }
2798 
2799 /*
2800  * Some boot consoles access data that is in the init section and which will
2801  * be discarded after the initcalls have been run. To make sure that no code
2802  * will access this data, unregister the boot consoles in a late initcall.
2803  *
2804  * If for some reason, such as deferred probe or the driver being a loadable
2805  * module, the real console hasn't registered yet at this point, there will
2806  * be a brief interval in which no messages are logged to the console, which
2807  * makes it difficult to diagnose problems that occur during this time.
2808  *
2809  * To mitigate this problem somewhat, only unregister consoles whose memory
2810  * intersects with the init section. Note that all other boot consoles will
2811  * get unregistred when the real preferred console is registered.
2812  */
2813 static int __init printk_late_init(void)
2814 {
2815         struct console *con;
2816         int ret;
2817 
2818         for_each_console(con) {
2819                 if (!(con->flags & CON_BOOT))
2820                         continue;
2821 
2822                 /* Check addresses that might be used for enabled consoles. */
2823                 if (init_section_intersects(con, sizeof(*con)) ||
2824                     init_section_contains(con->write, 0) ||
2825                     init_section_contains(con->read, 0) ||
2826                     init_section_contains(con->device, 0) ||
2827                     init_section_contains(con->unblank, 0) ||
2828                     init_section_contains(con->data, 0)) {
2829                         /*
2830                          * Please, consider moving the reported consoles out
2831                          * of the init section.
2832                          */
2833                         pr_warn("bootconsole [%s%d] uses init memory and must be disabled even before the real one is ready\n",
2834                                 con->name, con->index);
2835                         unregister_console(con);
2836                 }
2837         }
2838         ret = cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD, "printk:dead", NULL,
2839                                         console_cpu_notify);
2840         WARN_ON(ret < 0);
2841         ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "printk:online",
2842                                         console_cpu_notify, NULL);
2843         WARN_ON(ret < 0);
2844         return 0;
2845 }
2846 late_initcall(printk_late_init);
2847 
2848 #if defined CONFIG_PRINTK
2849 /*
2850  * Delayed printk version, for scheduler-internal messages:
2851  */
2852 #define PRINTK_PENDING_WAKEUP   0x01
2853 #define PRINTK_PENDING_OUTPUT   0x02
2854 
2855 static DEFINE_PER_CPU(int, printk_pending);
2856 
2857 static void wake_up_klogd_work_func(struct irq_work *irq_work)
2858 {
2859         int pending = __this_cpu_xchg(printk_pending, 0);
2860 
2861         if (pending & PRINTK_PENDING_OUTPUT) {
2862                 /* If trylock fails, someone else is doing the printing */
2863                 if (console_trylock())
2864                         console_unlock();
2865         }
2866 
2867         if (pending & PRINTK_PENDING_WAKEUP)
2868                 wake_up_interruptible(&log_wait);
2869 }
2870 
2871 static DEFINE_PER_CPU(struct irq_work, wake_up_klogd_work) = {
2872         .func = wake_up_klogd_work_func,
2873         .flags = IRQ_WORK_LAZY,
2874 };
2875 
2876 void wake_up_klogd(void)
2877 {
2878         preempt_disable();
2879         if (waitqueue_active(&log_wait)) {
2880                 this_cpu_or(printk_pending, PRINTK_PENDING_WAKEUP);
2881                 irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
2882         }
2883         preempt_enable();
2884 }
2885 
2886 int vprintk_deferred(const char *fmt, va_list args)
2887 {
2888         int r;
2889 
2890         r = vprintk_emit(0, LOGLEVEL_SCHED, NULL, 0, fmt, args);
2891 
2892         preempt_disable();
2893         __this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
2894         irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
2895         preempt_enable();
2896 
2897         return r;
2898 }
2899 
2900 int printk_deferred(const char *fmt, ...)
2901 {
2902         va_list args;
2903         int r;
2904 
2905         va_start(args, fmt);
2906         r = vprintk_deferred(fmt, args);
2907         va_end(args);
2908 
2909         return r;
2910 }
2911 
2912 /*
2913  * printk rate limiting, lifted from the networking subsystem.
2914  *
2915  * This enforces a rate limit: not more than 10 kernel messages
2916  * every 5s to make a denial-of-service attack impossible.
2917  */
2918 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
2919 
2920 int __printk_ratelimit(const char *func)
2921 {
2922         return ___ratelimit(&printk_ratelimit_state, func);
2923 }
2924 EXPORT_SYMBOL(__printk_ratelimit);
2925 
2926 /**
2927  * printk_timed_ratelimit - caller-controlled printk ratelimiting
2928  * @caller_jiffies: pointer to caller's state
2929  * @interval_msecs: minimum interval between prints
2930  *
2931  * printk_timed_ratelimit() returns true if more than @interval_msecs
2932  * milliseconds have elapsed since the last time printk_timed_ratelimit()
2933  * returned true.
2934  */
2935 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
2936                         unsigned int interval_msecs)
2937 {
2938         unsigned long elapsed = jiffies - *caller_jiffies;
2939 
2940         if (*caller_jiffies && elapsed <= msecs_to_jiffies(interval_msecs))
2941                 return false;
2942 
2943         *caller_jiffies = jiffies;
2944         return true;
2945 }
2946 EXPORT_SYMBOL(printk_timed_ratelimit);
2947 
2948 static DEFINE_SPINLOCK(dump_list_lock);
2949 static LIST_HEAD(dump_list);
2950 
2951 /**
2952  * kmsg_dump_register - register a kernel log dumper.
2953  * @dumper: pointer to the kmsg_dumper structure
2954  *
2955  * Adds a kernel log dumper to the system. The dump callback in the
2956  * structure will be called when the kernel oopses or panics and must be
2957  * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
2958  */
2959 int kmsg_dump_register(struct kmsg_dumper *dumper)
2960 {
2961         unsigned long flags;
2962         int err = -EBUSY;
2963 
2964         /* The dump callback needs to be set */
2965         if (!dumper->dump)
2966                 return -EINVAL;
2967 
2968         spin_lock_irqsave(&dump_list_lock, flags);
2969         /* Don't allow registering multiple times */
2970         if (!dumper->registered) {
2971                 dumper->registered = 1;
2972                 list_add_tail_rcu(&dumper->list, &dump_list);
2973                 err = 0;
2974         }
2975         spin_unlock_irqrestore(&dump_list_lock, flags);
2976 
2977         return err;
2978 }
2979 EXPORT_SYMBOL_GPL(kmsg_dump_register);
2980 
2981 /**
2982  * kmsg_dump_unregister - unregister a kmsg dumper.
2983  * @dumper: pointer to the kmsg_dumper structure
2984  *
2985  * Removes a dump device from the system. Returns zero on success and
2986  * %-EINVAL otherwise.
2987  */
2988 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
2989 {
2990         unsigned long flags;
2991         int err = -EINVAL;
2992 
2993         spin_lock_irqsave(&dump_list_lock, flags);
2994         if (dumper->registered) {
2995                 dumper->registered = 0;
2996                 list_del_rcu(&dumper->list);
2997                 err = 0;
2998         }
2999         spin_unlock_irqrestore(&dump_list_lock, flags);
3000         synchronize_rcu();
3001 
3002         return err;
3003 }
3004 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
3005 
3006 static bool always_kmsg_dump;
3007 module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);
3008 
3009 /**
3010  * kmsg_dump - dump kernel log to kernel message dumpers.
3011  * @reason: the reason (oops, panic etc) for dumping
3012  *
3013  * Call each of the registered dumper's dump() callback, which can
3014  * retrieve the kmsg records with kmsg_dump_get_line() or
3015  * kmsg_dump_get_buffer().
3016  */
3017 void kmsg_dump(enum kmsg_dump_reason reason)
3018 {
3019         struct kmsg_dumper *dumper;
3020         unsigned long flags;
3021 
3022         if ((reason > KMSG_DUMP_OOPS) && !always_kmsg_dump)
3023                 return;
3024 
3025         rcu_read_lock();
3026         list_for_each_entry_rcu(dumper, &dump_list, list) {
3027                 if (dumper->max_reason && reason > dumper->max_reason)
3028                         continue;
3029 
3030                 /* initialize iterator with data about the stored records */
3031                 dumper->active = true;
3032 
3033                 logbuf_lock_irqsave(flags);
3034                 dumper->cur_seq = clear_seq;
3035                 dumper->cur_idx = clear_idx;
3036                 dumper->next_seq = log_next_seq;
3037                 dumper->next_idx = log_next_idx;
3038                 logbuf_unlock_irqrestore(flags);
3039 
3040                 /* invoke dumper which will iterate over records */
3041                 dumper->dump(dumper, reason);
3042 
3043                 /* reset iterator */
3044                 dumper->active = false;
3045         }
3046         rcu_read_unlock();
3047 }
3048 
3049 /**
3050  * kmsg_dump_get_line_nolock - retrieve one kmsg log line (unlocked version)
3051  * @dumper: registered kmsg dumper
3052  * @syslog: include the "<4>" prefixes
3053  * @line: buffer to copy the line to
3054  * @size: maximum size of the buffer
3055  * @len: length of line placed into buffer
3056  *
3057  * Start at the beginning of the kmsg buffer, with the oldest kmsg
3058  * record, and copy one record into the provided buffer.
3059  *
3060  * Consecutive calls will return the next available record moving
3061  * towards the end of the buffer with the youngest messages.
3062  *
3063  * A return value of FALSE indicates that there are no more records to
3064  * read.
3065  *
3066  * The function is similar to kmsg_dump_get_line(), but grabs no locks.
3067  */
3068 bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
3069                                char *line, size_t size, size_t *len)
3070 {
3071         struct printk_log *msg;
3072         size_t l = 0;
3073         bool ret = false;
3074 
3075         if (!dumper->active)
3076                 goto out;
3077 
3078         if (dumper->cur_seq < log_first_seq) {
3079                 /* messages are gone, move to first available one */
3080                 dumper->cur_seq = log_first_seq;
3081                 dumper->cur_idx = log_first_idx;
3082         }
3083 
3084         /* last entry */
3085         if (dumper->cur_seq >= log_next_seq)
3086                 goto out;
3087 
3088         msg = log_from_idx(dumper->cur_idx);
3089         l = msg_print_text(msg, syslog, line, size);
3090 
3091         dumper->cur_idx = log_next(dumper->cur_idx);
3092         dumper->cur_seq++;
3093         ret = true;
3094 out:
3095         if (len)
3096                 *len = l;
3097         return ret;
3098 }
3099 
3100 /**
3101  * kmsg_dump_get_line - retrieve one kmsg log line
3102  * @dumper: registered kmsg dumper
3103  * @syslog: include the "<4>" prefixes
3104  * @line: buffer to copy the line to
3105  * @size: maximum size of the buffer
3106  * @len: length of line placed into buffer
3107  *
3108  * Start at the beginning of the kmsg buffer, with the oldest kmsg
3109  * record, and copy one record into the provided buffer.
3110  *
3111  * Consecutive calls will return the next available record moving
3112  * towards the end of the buffer with the youngest messages.
3113  *
3114  * A return value of FALSE indicates that there are no more records to
3115  * read.
3116  */
3117 bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
3118                         char *line, size_t size, size_t *len)
3119 {
3120         unsigned long flags;
3121         bool ret;
3122 
3123         logbuf_lock_irqsave(flags);
3124         ret = kmsg_dump_get_line_nolock(dumper, syslog, line, size, len);
3125         logbuf_unlock_irqrestore(flags);
3126 
3127         return ret;
3128 }
3129 EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
3130 
3131 /**
3132  * kmsg_dump_get_buffer - copy kmsg log lines
3133  * @dumper: registered kmsg dumper
3134  * @syslog: include the "<4>" prefixes
3135  * @buf: buffer to copy the line to
3136  * @size: maximum size of the buffer
3137  * @len: length of line placed into buffer
3138  *
3139  * Start at the end of the kmsg buffer and fill the provided buffer
3140  * with as many of the the *youngest* kmsg records that fit into it.
3141  * If the buffer is large enough, all available kmsg records will be
3142  * copied with a single call.
3143  *
3144  * Consecutive calls will fill the buffer with the next block of
3145  * available older records, not including the earlier retrieved ones.
3146  *
3147  * A return value of FALSE indicates that there are no more records to
3148  * read.
3149  */
3150 bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
3151                           char *buf, size_t size, size_t *len)
3152 {
3153         unsigned long flags;
3154         u64 seq;
3155         u32 idx;
3156         u64 next_seq;
3157         u32 next_idx;
3158         size_t l = 0;
3159         bool ret = false;
3160 
3161         if (!dumper->active)
3162                 goto out;
3163 
3164         logbuf_lock_irqsave(flags);
3165         if (dumper->cur_seq < log_first_seq) {
3166                 /* messages are gone, move to first available one */
3167                 dumper->cur_seq = log_first_seq;
3168                 dumper->cur_idx = log_first_idx;
3169         }
3170 
3171         /* last entry */
3172         if (dumper->cur_seq >= dumper->next_seq) {
3173                 logbuf_unlock_irqrestore(flags);
3174                 goto out;
3175         }
3176 
3177         /* calculate length of entire buffer */
3178         seq = dumper->cur_seq;
3179         idx = dumper->cur_idx;
3180         while (seq < dumper->next_seq) {
3181                 struct printk_log *msg = log_from_idx(idx);
3182 
3183                 l += msg_print_text(msg, true, NULL, 0);
3184                 idx = log_next(idx);
3185                 seq++;
3186         }
3187 
3188         /* move first record forward until length fits into the buffer */
3189         seq = dumper->cur_seq;
3190         idx = dumper->cur_idx;
3191         while (l > size && seq < dumper->next_seq) {
3192                 struct printk_log *msg = log_from_idx(idx);
3193 
3194                 l -= msg_print_text(msg, true, NULL, 0);
3195                 idx = log_next(idx);
3196                 seq++;
3197         }
3198 
3199         /* last message in next interation */
3200         next_seq = seq;
3201         next_idx = idx;
3202 
3203         l = 0;
3204         while (seq < dumper->next_seq) {
3205                 struct printk_log *msg = log_from_idx(idx);
3206 
3207                 l += msg_print_text(msg, syslog, buf + l, size - l);
3208                 idx = log_next(idx);
3209                 seq++;
3210         }
3211 
3212         dumper->next_seq = next_seq;
3213         dumper->next_idx = next_idx;
3214         ret = true;
3215         logbuf_unlock_irqrestore(flags);
3216 out:
3217         if (len)
3218                 *len = l;
3219         return ret;
3220 }
3221 EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
3222 
3223 /**
3224  * kmsg_dump_rewind_nolock - reset the interator (unlocked version)
3225  * @dumper: registered kmsg dumper
3226  *
3227  * Reset the dumper's iterator so that kmsg_dump_get_line() and
3228  * kmsg_dump_get_buffer() can be called again and used multiple
3229  * times within the same dumper.dump() callback.
3230  *
3231  * The function is similar to kmsg_dump_rewind(), but grabs no locks.
3232  */
3233 void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
3234 {
3235         dumper->cur_seq = clear_seq;
3236         dumper->cur_idx = clear_idx;
3237         dumper->next_seq = log_next_seq;
3238         dumper->next_idx = log_next_idx;
3239 }
3240 
3241 /**
3242  * kmsg_dump_rewind - reset the interator
3243  * @dumper: registered kmsg dumper
3244  *
3245  * Reset the dumper's iterator so that kmsg_dump_get_line() and
3246  * kmsg_dump_get_buffer() can be called again and used multiple
3247  * times within the same dumper.dump() callback.
3248  */
3249 void kmsg_dump_rewind(struct kmsg_dumper *dumper)
3250 {
3251         unsigned long flags;
3252 
3253         logbuf_lock_irqsave(flags);
3254         kmsg_dump_rewind_nolock(dumper);
3255         logbuf_unlock_irqrestore(flags);
3256 }
3257 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
3258 
3259 static char dump_stack_arch_desc_str[128];
3260 
3261 /**
3262  * dump_stack_set_arch_desc - set arch-specific str to show with task dumps
3263  * @fmt: printf-style format string
3264  * @...: arguments for the format string
3265  *
3266  * The configured string will be printed right after utsname during task
3267  * dumps.  Usually used to add arch-specific system identifiers.  If an
3268  * arch wants to make use of such an ID string, it should initialize this
3269  * as soon as possible during boot.
3270  */
3271 void __init dump_stack_set_arch_desc(const char *fmt, ...)
3272 {
3273         va_list args;
3274 
3275         va_start(args, fmt);
3276         vsnprintf(dump_stack_arch_desc_str, sizeof(dump_stack_arch_desc_str),
3277                   fmt, args);
3278         va_end(args);
3279 }
3280 
3281 /**
3282  * dump_stack_print_info - print generic debug info for dump_stack()
3283  * @log_lvl: log level
3284  *
3285  * Arch-specific dump_stack() implementations can use this function to
3286  * print out the same debug information as the generic dump_stack().
3287  */
3288 void dump_stack_print_info(const char *log_lvl)
3289 {
3290         printk("%sCPU: %d PID: %d Comm: %.20s %s %s %.*s\n",
3291                log_lvl, raw_smp_processor_id(), current->pid, current->comm,
3292                print_tainted(), init_utsname()->release,
3293                (int)strcspn(init_utsname()->version, " "),
3294                init_utsname()->version);
3295 
3296         if (dump_stack_arch_desc_str[0] != '\0')
3297                 printk("%sHardware name: %s\n",
3298                        log_lvl, dump_stack_arch_desc_str);
3299 
3300         print_worker_info(log_lvl, current);
3301 }
3302 
3303 /**
3304  * show_regs_print_info - print generic debug info for show_regs()
3305  * @log_lvl: log level
3306  *
3307  * show_regs() implementations can use this function to print out generic
3308  * debug information.
3309  */
3310 void show_regs_print_info(const char *log_lvl)
3311 {
3312         dump_stack_print_info(log_lvl);
3313 }
3314 
3315 #endif
3316 

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