1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * linux/kernel/panic.c
4 *
5 * Copyright (C) 1991, 1992 Linus Torvalds
6 */
7
8/*
9 * This function is used through-out the kernel (including mm and fs)
10 * to indicate a major problem.
11 */
12#include <linux/debug_locks.h>
13#include <linux/sched/debug.h>
14#include <linux/interrupt.h>
15#include <linux/kgdb.h>
16#include <linux/kmsg_dump.h>
17#include <linux/kallsyms.h>
18#include <linux/notifier.h>
19#include <linux/vt_kern.h>
20#include <linux/module.h>
21#include <linux/random.h>
22#include <linux/ftrace.h>
23#include <linux/reboot.h>
24#include <linux/delay.h>
25#include <linux/kexec.h>
26#include <linux/panic_notifier.h>
27#include <linux/sched.h>
28#include <linux/string_helpers.h>
29#include <linux/sysrq.h>
30#include <linux/init.h>
31#include <linux/nmi.h>
32#include <linux/console.h>
33#include <linux/bug.h>
34#include <linux/ratelimit.h>
35#include <linux/debugfs.h>
36#include <linux/sysfs.h>
37#include <linux/context_tracking.h>
38#include <linux/seq_buf.h>
39#include <trace/events/error_report.h>
40#include <asm/sections.h>
41
42#define PANIC_TIMER_STEP 100
43#define PANIC_BLINK_SPD 18
44
45#ifdef CONFIG_SMP
46/*
47 * Should we dump all CPUs backtraces in an oops event?
48 * Defaults to 0, can be changed via sysctl.
49 */
50static unsigned int __read_mostly sysctl_oops_all_cpu_backtrace;
51#else
52#define sysctl_oops_all_cpu_backtrace 0
53#endif /* CONFIG_SMP */
54
55int panic_on_oops = CONFIG_PANIC_ON_OOPS_VALUE;
56static unsigned long tainted_mask =
57 IS_ENABLED(CONFIG_RANDSTRUCT) ? (1 << TAINT_RANDSTRUCT) : 0;
58static int pause_on_oops;
59static int pause_on_oops_flag;
60static DEFINE_SPINLOCK(pause_on_oops_lock);
61bool crash_kexec_post_notifiers;
62int panic_on_warn __read_mostly;
63unsigned long panic_on_taint;
64bool panic_on_taint_nousertaint = false;
65static unsigned int warn_limit __read_mostly;
66
67bool panic_triggering_all_cpu_backtrace;
68
69int panic_timeout = CONFIG_PANIC_TIMEOUT;
70EXPORT_SYMBOL_GPL(panic_timeout);
71
72#define PANIC_PRINT_TASK_INFO 0x00000001
73#define PANIC_PRINT_MEM_INFO 0x00000002
74#define PANIC_PRINT_TIMER_INFO 0x00000004
75#define PANIC_PRINT_LOCK_INFO 0x00000008
76#define PANIC_PRINT_FTRACE_INFO 0x00000010
77#define PANIC_PRINT_ALL_PRINTK_MSG 0x00000020
78#define PANIC_PRINT_ALL_CPU_BT 0x00000040
79#define PANIC_PRINT_BLOCKED_TASKS 0x00000080
80unsigned long panic_print;
81
82ATOMIC_NOTIFIER_HEAD(panic_notifier_list);
83
84EXPORT_SYMBOL(panic_notifier_list);
85
86#ifdef CONFIG_SYSCTL
87static const struct ctl_table kern_panic_table[] = {
88#ifdef CONFIG_SMP
89 {
90 .procname = "oops_all_cpu_backtrace",
91 .data = &sysctl_oops_all_cpu_backtrace,
92 .maxlen = sizeof(int),
93 .mode = 0644,
94 .proc_handler = proc_dointvec_minmax,
95 .extra1 = SYSCTL_ZERO,
96 .extra2 = SYSCTL_ONE,
97 },
98#endif
99 {
100 .procname = "panic",
101 .data = &panic_timeout,
102 .maxlen = sizeof(int),
103 .mode = 0644,
104 .proc_handler = proc_dointvec,
105 },
106 {
107 .procname = "panic_on_oops",
108 .data = &panic_on_oops,
109 .maxlen = sizeof(int),
110 .mode = 0644,
111 .proc_handler = proc_dointvec,
112 },
113 {
114 .procname = "panic_print",
115 .data = &panic_print,
116 .maxlen = sizeof(unsigned long),
117 .mode = 0644,
118 .proc_handler = proc_doulongvec_minmax,
119 },
120 {
121 .procname = "panic_on_warn",
122 .data = &panic_on_warn,
123 .maxlen = sizeof(int),
124 .mode = 0644,
125 .proc_handler = proc_dointvec_minmax,
126 .extra1 = SYSCTL_ZERO,
127 .extra2 = SYSCTL_ONE,
128 },
129 {
130 .procname = "warn_limit",
131 .data = &warn_limit,
132 .maxlen = sizeof(warn_limit),
133 .mode = 0644,
134 .proc_handler = proc_douintvec,
135 },
136};
137
138static __init int kernel_panic_sysctls_init(void)
139{
140 register_sysctl_init("kernel", kern_panic_table);
141 return 0;
142}
143late_initcall(kernel_panic_sysctls_init);
144#endif
145
146static atomic_t warn_count = ATOMIC_INIT(0);
147
148#ifdef CONFIG_SYSFS
149static ssize_t warn_count_show(struct kobject *kobj, struct kobj_attribute *attr,
150 char *page)
151{
152 return sysfs_emit(buf: page, fmt: "%d\n", atomic_read(v: &warn_count));
153}
154
155static struct kobj_attribute warn_count_attr = __ATTR_RO(warn_count);
156
157static __init int kernel_panic_sysfs_init(void)
158{
159 sysfs_add_file_to_group(kobj: kernel_kobj, attr: &warn_count_attr.attr, NULL);
160 return 0;
161}
162late_initcall(kernel_panic_sysfs_init);
163#endif
164
165static long no_blink(int state)
166{
167 return 0;
168}
169
170/* Returns how long it waited in ms */
171long (*panic_blink)(int state);
172EXPORT_SYMBOL(panic_blink);
173
174/*
175 * Stop ourself in panic -- architecture code may override this
176 */
177void __weak __noreturn panic_smp_self_stop(void)
178{
179 while (1)
180 cpu_relax();
181}
182
183/*
184 * Stop ourselves in NMI context if another CPU has already panicked. Arch code
185 * may override this to prepare for crash dumping, e.g. save regs info.
186 */
187void __weak __noreturn nmi_panic_self_stop(struct pt_regs *regs)
188{
189 panic_smp_self_stop();
190}
191
192/*
193 * Stop other CPUs in panic. Architecture dependent code may override this
194 * with more suitable version. For example, if the architecture supports
195 * crash dump, it should save registers of each stopped CPU and disable
196 * per-CPU features such as virtualization extensions.
197 */
198void __weak crash_smp_send_stop(void)
199{
200 static int cpus_stopped;
201
202 /*
203 * This function can be called twice in panic path, but obviously
204 * we execute this only once.
205 */
206 if (cpus_stopped)
207 return;
208
209 /*
210 * Note smp_send_stop is the usual smp shutdown function, which
211 * unfortunately means it may not be hardened to work in a panic
212 * situation.
213 */
214 smp_send_stop();
215 cpus_stopped = 1;
216}
217
218atomic_t panic_cpu = ATOMIC_INIT(PANIC_CPU_INVALID);
219
220/*
221 * A variant of panic() called from NMI context. We return if we've already
222 * panicked on this CPU. If another CPU already panicked, loop in
223 * nmi_panic_self_stop() which can provide architecture dependent code such
224 * as saving register state for crash dump.
225 */
226void nmi_panic(struct pt_regs *regs, const char *msg)
227{
228 int old_cpu, this_cpu;
229
230 old_cpu = PANIC_CPU_INVALID;
231 this_cpu = raw_smp_processor_id();
232
233 /* atomic_try_cmpxchg updates old_cpu on failure */
234 if (atomic_try_cmpxchg(v: &panic_cpu, old: &old_cpu, new: this_cpu))
235 panic(fmt: "%s", msg);
236 else if (old_cpu != this_cpu)
237 nmi_panic_self_stop(regs);
238}
239EXPORT_SYMBOL(nmi_panic);
240
241static void panic_print_sys_info(bool console_flush)
242{
243 if (console_flush) {
244 if (panic_print & PANIC_PRINT_ALL_PRINTK_MSG)
245 console_flush_on_panic(mode: CONSOLE_REPLAY_ALL);
246 return;
247 }
248
249 if (panic_print & PANIC_PRINT_TASK_INFO)
250 show_state();
251
252 if (panic_print & PANIC_PRINT_MEM_INFO)
253 show_mem();
254
255 if (panic_print & PANIC_PRINT_TIMER_INFO)
256 sysrq_timer_list_show();
257
258 if (panic_print & PANIC_PRINT_LOCK_INFO)
259 debug_show_all_locks();
260
261 if (panic_print & PANIC_PRINT_FTRACE_INFO)
262 ftrace_dump(oops_dump_mode: DUMP_ALL);
263
264 if (panic_print & PANIC_PRINT_BLOCKED_TASKS)
265 show_state_filter(TASK_UNINTERRUPTIBLE);
266}
267
268void check_panic_on_warn(const char *origin)
269{
270 unsigned int limit;
271
272 if (panic_on_warn)
273 panic(fmt: "%s: panic_on_warn set ...\n", origin);
274
275 limit = READ_ONCE(warn_limit);
276 if (atomic_inc_return(v: &warn_count) >= limit && limit)
277 panic(fmt: "%s: system warned too often (kernel.warn_limit is %d)",
278 origin, limit);
279}
280
281/*
282 * Helper that triggers the NMI backtrace (if set in panic_print)
283 * and then performs the secondary CPUs shutdown - we cannot have
284 * the NMI backtrace after the CPUs are off!
285 */
286static void panic_other_cpus_shutdown(bool crash_kexec)
287{
288 if (panic_print & PANIC_PRINT_ALL_CPU_BT) {
289 /* Temporary allow non-panic CPUs to write their backtraces. */
290 panic_triggering_all_cpu_backtrace = true;
291 trigger_all_cpu_backtrace();
292 panic_triggering_all_cpu_backtrace = false;
293 }
294
295 /*
296 * Note that smp_send_stop() is the usual SMP shutdown function,
297 * which unfortunately may not be hardened to work in a panic
298 * situation. If we want to do crash dump after notifier calls
299 * and kmsg_dump, we will need architecture dependent extra
300 * bits in addition to stopping other CPUs, hence we rely on
301 * crash_smp_send_stop() for that.
302 */
303 if (!crash_kexec)
304 smp_send_stop();
305 else
306 crash_smp_send_stop();
307}
308
309/**
310 * panic - halt the system
311 * @fmt: The text string to print
312 *
313 * Display a message, then perform cleanups. This function never returns.
314 */
315void panic(const char *fmt, ...)
316{
317 static char buf[1024];
318 va_list args;
319 long i, i_next = 0, len;
320 int state = 0;
321 int old_cpu, this_cpu;
322 bool _crash_kexec_post_notifiers = crash_kexec_post_notifiers;
323
324 if (panic_on_warn) {
325 /*
326 * This thread may hit another WARN() in the panic path.
327 * Resetting this prevents additional WARN() from panicking the
328 * system on this thread. Other threads are blocked by the
329 * panic_mutex in panic().
330 */
331 panic_on_warn = 0;
332 }
333
334 /*
335 * Disable local interrupts. This will prevent panic_smp_self_stop
336 * from deadlocking the first cpu that invokes the panic, since
337 * there is nothing to prevent an interrupt handler (that runs
338 * after setting panic_cpu) from invoking panic() again.
339 */
340 local_irq_disable();
341 preempt_disable_notrace();
342
343 /*
344 * It's possible to come here directly from a panic-assertion and
345 * not have preempt disabled. Some functions called from here want
346 * preempt to be disabled. No point enabling it later though...
347 *
348 * Only one CPU is allowed to execute the panic code from here. For
349 * multiple parallel invocations of panic, all other CPUs either
350 * stop themself or will wait until they are stopped by the 1st CPU
351 * with smp_send_stop().
352 *
353 * cmpxchg success means this is the 1st CPU which comes here,
354 * so go ahead.
355 * `old_cpu == this_cpu' means we came from nmi_panic() which sets
356 * panic_cpu to this CPU. In this case, this is also the 1st CPU.
357 */
358 old_cpu = PANIC_CPU_INVALID;
359 this_cpu = raw_smp_processor_id();
360
361 /* atomic_try_cmpxchg updates old_cpu on failure */
362 if (atomic_try_cmpxchg(v: &panic_cpu, old: &old_cpu, new: this_cpu)) {
363 /* go ahead */
364 } else if (old_cpu != this_cpu)
365 panic_smp_self_stop();
366
367 console_verbose();
368 bust_spinlocks(yes: 1);
369 va_start(args, fmt);
370 len = vscnprintf(buf, size: sizeof(buf), fmt, args);
371 va_end(args);
372
373 if (len && buf[len - 1] == '\n')
374 buf[len - 1] = '\0';
375
376 pr_emerg("Kernel panic - not syncing: %s\n", buf);
377#ifdef CONFIG_DEBUG_BUGVERBOSE
378 /*
379 * Avoid nested stack-dumping if a panic occurs during oops processing
380 */
381 if (!test_taint(TAINT_DIE) && oops_in_progress <= 1)
382 dump_stack();
383#endif
384
385 /*
386 * If kgdb is enabled, give it a chance to run before we stop all
387 * the other CPUs or else we won't be able to debug processes left
388 * running on them.
389 */
390 kgdb_panic(msg: buf);
391
392 /*
393 * If we have crashed and we have a crash kernel loaded let it handle
394 * everything else.
395 * If we want to run this after calling panic_notifiers, pass
396 * the "crash_kexec_post_notifiers" option to the kernel.
397 *
398 * Bypass the panic_cpu check and call __crash_kexec directly.
399 */
400 if (!_crash_kexec_post_notifiers)
401 __crash_kexec(NULL);
402
403 panic_other_cpus_shutdown(crash_kexec: _crash_kexec_post_notifiers);
404
405 printk_legacy_allow_panic_sync();
406
407 /*
408 * Run any panic handlers, including those that might need to
409 * add information to the kmsg dump output.
410 */
411 atomic_notifier_call_chain(nh: &panic_notifier_list, val: 0, v: buf);
412
413 panic_print_sys_info(console_flush: false);
414
415 kmsg_dump_desc(reason: KMSG_DUMP_PANIC, desc: buf);
416
417 /*
418 * If you doubt kdump always works fine in any situation,
419 * "crash_kexec_post_notifiers" offers you a chance to run
420 * panic_notifiers and dumping kmsg before kdump.
421 * Note: since some panic_notifiers can make crashed kernel
422 * more unstable, it can increase risks of the kdump failure too.
423 *
424 * Bypass the panic_cpu check and call __crash_kexec directly.
425 */
426 if (_crash_kexec_post_notifiers)
427 __crash_kexec(NULL);
428
429 console_unblank();
430
431 /*
432 * We may have ended up stopping the CPU holding the lock (in
433 * smp_send_stop()) while still having some valuable data in the console
434 * buffer. Try to acquire the lock then release it regardless of the
435 * result. The release will also print the buffers out. Locks debug
436 * should be disabled to avoid reporting bad unlock balance when
437 * panic() is not being callled from OOPS.
438 */
439 debug_locks_off();
440 console_flush_on_panic(mode: CONSOLE_FLUSH_PENDING);
441
442 panic_print_sys_info(console_flush: true);
443
444 if (!panic_blink)
445 panic_blink = no_blink;
446
447 if (panic_timeout > 0) {
448 /*
449 * Delay timeout seconds before rebooting the machine.
450 * We can't use the "normal" timers since we just panicked.
451 */
452 pr_emerg("Rebooting in %d seconds..\n", panic_timeout);
453
454 for (i = 0; i < panic_timeout * 1000; i += PANIC_TIMER_STEP) {
455 touch_nmi_watchdog();
456 if (i >= i_next) {
457 i += panic_blink(state ^= 1);
458 i_next = i + 3600 / PANIC_BLINK_SPD;
459 }
460 mdelay(PANIC_TIMER_STEP);
461 }
462 }
463 if (panic_timeout != 0) {
464 /*
465 * This will not be a clean reboot, with everything
466 * shutting down. But if there is a chance of
467 * rebooting the system it will be rebooted.
468 */
469 if (panic_reboot_mode != REBOOT_UNDEFINED)
470 reboot_mode = panic_reboot_mode;
471 emergency_restart();
472 }
473#ifdef __sparc__
474 {
475 extern int stop_a_enabled;
476 /* Make sure the user can actually press Stop-A (L1-A) */
477 stop_a_enabled = 1;
478 pr_emerg("Press Stop-A (L1-A) from sun keyboard or send break\n"
479 "twice on console to return to the boot prom\n");
480 }
481#endif
482#if defined(CONFIG_S390)
483 disabled_wait();
484#endif
485 pr_emerg("---[ end Kernel panic - not syncing: %s ]---\n", buf);
486
487 /* Do not scroll important messages printed above */
488 suppress_printk = 1;
489
490 /*
491 * The final messages may not have been printed if in a context that
492 * defers printing (such as NMI) and irq_work is not available.
493 * Explicitly flush the kernel log buffer one last time.
494 */
495 console_flush_on_panic(mode: CONSOLE_FLUSH_PENDING);
496 nbcon_atomic_flush_unsafe();
497
498 local_irq_enable();
499 for (i = 0; ; i += PANIC_TIMER_STEP) {
500 touch_softlockup_watchdog();
501 if (i >= i_next) {
502 i += panic_blink(state ^= 1);
503 i_next = i + 3600 / PANIC_BLINK_SPD;
504 }
505 mdelay(PANIC_TIMER_STEP);
506 }
507}
508
509EXPORT_SYMBOL(panic);
510
511#define TAINT_FLAG(taint, _c_true, _c_false, _module) \
512 [ TAINT_##taint ] = { \
513 .c_true = _c_true, .c_false = _c_false, \
514 .module = _module, \
515 .desc = #taint, \
516 }
517
518/*
519 * TAINT_FORCED_RMMOD could be a per-module flag but the module
520 * is being removed anyway.
521 */
522const struct taint_flag taint_flags[TAINT_FLAGS_COUNT] = {
523 TAINT_FLAG(PROPRIETARY_MODULE, 'P', 'G', true),
524 TAINT_FLAG(FORCED_MODULE, 'F', ' ', true),
525 TAINT_FLAG(CPU_OUT_OF_SPEC, 'S', ' ', false),
526 TAINT_FLAG(FORCED_RMMOD, 'R', ' ', false),
527 TAINT_FLAG(MACHINE_CHECK, 'M', ' ', false),
528 TAINT_FLAG(BAD_PAGE, 'B', ' ', false),
529 TAINT_FLAG(USER, 'U', ' ', false),
530 TAINT_FLAG(DIE, 'D', ' ', false),
531 TAINT_FLAG(OVERRIDDEN_ACPI_TABLE, 'A', ' ', false),
532 TAINT_FLAG(WARN, 'W', ' ', false),
533 TAINT_FLAG(CRAP, 'C', ' ', true),
534 TAINT_FLAG(FIRMWARE_WORKAROUND, 'I', ' ', false),
535 TAINT_FLAG(OOT_MODULE, 'O', ' ', true),
536 TAINT_FLAG(UNSIGNED_MODULE, 'E', ' ', true),
537 TAINT_FLAG(SOFTLOCKUP, 'L', ' ', false),
538 TAINT_FLAG(LIVEPATCH, 'K', ' ', true),
539 TAINT_FLAG(AUX, 'X', ' ', true),
540 TAINT_FLAG(RANDSTRUCT, 'T', ' ', true),
541 TAINT_FLAG(TEST, 'N', ' ', true),
542 TAINT_FLAG(FWCTL, 'J', ' ', true),
543};
544
545#undef TAINT_FLAG
546
547static void print_tainted_seq(struct seq_buf *s, bool verbose)
548{
549 const char *sep = "";
550 int i;
551
552 if (!tainted_mask) {
553 seq_buf_puts(s, str: "Not tainted");
554 return;
555 }
556
557 seq_buf_printf(s, fmt: "Tainted: ");
558 for (i = 0; i < TAINT_FLAGS_COUNT; i++) {
559 const struct taint_flag *t = &taint_flags[i];
560 bool is_set = test_bit(i, &tainted_mask);
561 char c = is_set ? t->c_true : t->c_false;
562
563 if (verbose) {
564 if (is_set) {
565 seq_buf_printf(s, fmt: "%s[%c]=%s", sep, c, t->desc);
566 sep = ", ";
567 }
568 } else {
569 seq_buf_putc(s, c);
570 }
571 }
572}
573
574static const char *_print_tainted(bool verbose)
575{
576 /* FIXME: what should the size be? */
577 static char buf[sizeof(taint_flags)];
578 struct seq_buf s;
579
580 BUILD_BUG_ON(ARRAY_SIZE(taint_flags) != TAINT_FLAGS_COUNT);
581
582 seq_buf_init(s: &s, buf, size: sizeof(buf));
583
584 print_tainted_seq(s: &s, verbose);
585
586 return seq_buf_str(s: &s);
587}
588
589/**
590 * print_tainted - return a string to represent the kernel taint state.
591 *
592 * For individual taint flag meanings, see Documentation/admin-guide/sysctl/kernel.rst
593 *
594 * The string is overwritten by the next call to print_tainted(),
595 * but is always NULL terminated.
596 */
597const char *print_tainted(void)
598{
599 return _print_tainted(verbose: false);
600}
601
602/**
603 * print_tainted_verbose - A more verbose version of print_tainted()
604 */
605const char *print_tainted_verbose(void)
606{
607 return _print_tainted(verbose: true);
608}
609
610int test_taint(unsigned flag)
611{
612 return test_bit(flag, &tainted_mask);
613}
614EXPORT_SYMBOL(test_taint);
615
616unsigned long get_taint(void)
617{
618 return tainted_mask;
619}
620
621/**
622 * add_taint: add a taint flag if not already set.
623 * @flag: one of the TAINT_* constants.
624 * @lockdep_ok: whether lock debugging is still OK.
625 *
626 * If something bad has gone wrong, you'll want @lockdebug_ok = false, but for
627 * some notewortht-but-not-corrupting cases, it can be set to true.
628 */
629void add_taint(unsigned flag, enum lockdep_ok lockdep_ok)
630{
631 if (lockdep_ok == LOCKDEP_NOW_UNRELIABLE && __debug_locks_off())
632 pr_warn("Disabling lock debugging due to kernel taint\n");
633
634 set_bit(nr: flag, addr: &tainted_mask);
635
636 if (tainted_mask & panic_on_taint) {
637 panic_on_taint = 0;
638 panic("panic_on_taint set ...");
639 }
640}
641EXPORT_SYMBOL(add_taint);
642
643static void spin_msec(int msecs)
644{
645 int i;
646
647 for (i = 0; i < msecs; i++) {
648 touch_nmi_watchdog();
649 mdelay(1);
650 }
651}
652
653/*
654 * It just happens that oops_enter() and oops_exit() are identically
655 * implemented...
656 */
657static void do_oops_enter_exit(void)
658{
659 unsigned long flags;
660 static int spin_counter;
661
662 if (!pause_on_oops)
663 return;
664
665 spin_lock_irqsave(&pause_on_oops_lock, flags);
666 if (pause_on_oops_flag == 0) {
667 /* This CPU may now print the oops message */
668 pause_on_oops_flag = 1;
669 } else {
670 /* We need to stall this CPU */
671 if (!spin_counter) {
672 /* This CPU gets to do the counting */
673 spin_counter = pause_on_oops;
674 do {
675 spin_unlock(lock: &pause_on_oops_lock);
676 spin_msec(MSEC_PER_SEC);
677 spin_lock(lock: &pause_on_oops_lock);
678 } while (--spin_counter);
679 pause_on_oops_flag = 0;
680 } else {
681 /* This CPU waits for a different one */
682 while (spin_counter) {
683 spin_unlock(lock: &pause_on_oops_lock);
684 spin_msec(msecs: 1);
685 spin_lock(lock: &pause_on_oops_lock);
686 }
687 }
688 }
689 spin_unlock_irqrestore(lock: &pause_on_oops_lock, flags);
690}
691
692/*
693 * Return true if the calling CPU is allowed to print oops-related info.
694 * This is a bit racy..
695 */
696bool oops_may_print(void)
697{
698 return pause_on_oops_flag == 0;
699}
700
701/*
702 * Called when the architecture enters its oops handler, before it prints
703 * anything. If this is the first CPU to oops, and it's oopsing the first
704 * time then let it proceed.
705 *
706 * This is all enabled by the pause_on_oops kernel boot option. We do all
707 * this to ensure that oopses don't scroll off the screen. It has the
708 * side-effect of preventing later-oopsing CPUs from mucking up the display,
709 * too.
710 *
711 * It turns out that the CPU which is allowed to print ends up pausing for
712 * the right duration, whereas all the other CPUs pause for twice as long:
713 * once in oops_enter(), once in oops_exit().
714 */
715void oops_enter(void)
716{
717 nbcon_cpu_emergency_enter();
718 tracing_off();
719 /* can't trust the integrity of the kernel anymore: */
720 debug_locks_off();
721 do_oops_enter_exit();
722
723 if (sysctl_oops_all_cpu_backtrace)
724 trigger_all_cpu_backtrace();
725}
726
727static void print_oops_end_marker(void)
728{
729 pr_warn("---[ end trace %016llx ]---\n", 0ULL);
730}
731
732/*
733 * Called when the architecture exits its oops handler, after printing
734 * everything.
735 */
736void oops_exit(void)
737{
738 do_oops_enter_exit();
739 print_oops_end_marker();
740 nbcon_cpu_emergency_exit();
741 kmsg_dump(reason: KMSG_DUMP_OOPS);
742}
743
744struct warn_args {
745 const char *fmt;
746 va_list args;
747};
748
749void __warn(const char *file, int line, void *caller, unsigned taint,
750 struct pt_regs *regs, struct warn_args *args)
751{
752 nbcon_cpu_emergency_enter();
753
754 disable_trace_on_warning();
755
756 if (file)
757 pr_warn("WARNING: CPU: %d PID: %d at %s:%d %pS\n",
758 raw_smp_processor_id(), current->pid, file, line,
759 caller);
760 else
761 pr_warn("WARNING: CPU: %d PID: %d at %pS\n",
762 raw_smp_processor_id(), current->pid, caller);
763
764#pragma GCC diagnostic push
765#ifndef __clang__
766#pragma GCC diagnostic ignored "-Wsuggest-attribute=format"
767#endif
768 if (args)
769 vprintk(fmt: args->fmt, args: args->args);
770#pragma GCC diagnostic pop
771
772 print_modules();
773
774 if (regs)
775 show_regs(regs);
776
777 check_panic_on_warn(origin: "kernel");
778
779 if (!regs)
780 dump_stack();
781
782 print_irqtrace_events(current);
783
784 print_oops_end_marker();
785 trace_error_report_end(error_detector: ERROR_DETECTOR_WARN, id: (unsigned long)caller);
786
787 /* Just a warning, don't kill lockdep. */
788 add_taint(taint, LOCKDEP_STILL_OK);
789
790 nbcon_cpu_emergency_exit();
791}
792
793#ifdef CONFIG_BUG
794#ifndef __WARN_FLAGS
795void warn_slowpath_fmt(const char *file, int line, unsigned taint,
796 const char *fmt, ...)
797{
798 bool rcu = warn_rcu_enter();
799 struct warn_args args;
800
801 pr_warn(CUT_HERE);
802
803 if (!fmt) {
804 __warn(file, line, __builtin_return_address(0), taint,
805 NULL, NULL);
806 warn_rcu_exit(rcu);
807 return;
808 }
809
810 args.fmt = fmt;
811 va_start(args.args, fmt);
812 __warn(file, line, __builtin_return_address(0), taint, NULL, &args);
813 va_end(args.args);
814 warn_rcu_exit(rcu);
815}
816EXPORT_SYMBOL(warn_slowpath_fmt);
817#else
818void __warn_printk(const char *fmt, ...)
819{
820 bool rcu = warn_rcu_enter();
821 va_list args;
822
823 pr_warn(CUT_HERE);
824
825 va_start(args, fmt);
826 vprintk(fmt, args);
827 va_end(args);
828 warn_rcu_exit(rcu);
829}
830EXPORT_SYMBOL(__warn_printk);
831#endif
832
833/* Support resetting WARN*_ONCE state */
834
835static int clear_warn_once_set(void *data, u64 val)
836{
837 generic_bug_clear_once();
838 memset(__start_once, 0, __end_once - __start_once);
839 return 0;
840}
841
842DEFINE_DEBUGFS_ATTRIBUTE(clear_warn_once_fops, NULL, clear_warn_once_set,
843 "%lld\n");
844
845static __init int register_warn_debugfs(void)
846{
847 /* Don't care about failure */
848 debugfs_create_file_unsafe(name: "clear_warn_once", mode: 0200, NULL, NULL,
849 fops: &clear_warn_once_fops);
850 return 0;
851}
852
853device_initcall(register_warn_debugfs);
854#endif
855
856#ifdef CONFIG_STACKPROTECTOR
857
858/*
859 * Called when gcc's -fstack-protector feature is used, and
860 * gcc detects corruption of the on-stack canary value
861 */
862__visible noinstr void __stack_chk_fail(void)
863{
864 unsigned long flags;
865
866 instrumentation_begin();
867 flags = user_access_save();
868
869 panic("stack-protector: Kernel stack is corrupted in: %pB",
870 __builtin_return_address(0));
871
872 user_access_restore(flags);
873 instrumentation_end();
874}
875EXPORT_SYMBOL(__stack_chk_fail);
876
877#endif
878
879core_param(panic, panic_timeout, int, 0644);
880core_param(panic_print, panic_print, ulong, 0644);
881core_param(pause_on_oops, pause_on_oops, int, 0644);
882core_param(panic_on_warn, panic_on_warn, int, 0644);
883core_param(crash_kexec_post_notifiers, crash_kexec_post_notifiers, bool, 0644);
884
885static int __init oops_setup(char *s)
886{
887 if (!s)
888 return -EINVAL;
889 if (!strcmp(s, "panic"))
890 panic_on_oops = 1;
891 return 0;
892}
893early_param("oops", oops_setup);
894
895static int __init panic_on_taint_setup(char *s)
896{
897 char *taint_str;
898
899 if (!s)
900 return -EINVAL;
901
902 taint_str = strsep(&s, ",");
903 if (kstrtoul(s: taint_str, base: 16, res: &panic_on_taint))
904 return -EINVAL;
905
906 /* make sure panic_on_taint doesn't hold out-of-range TAINT flags */
907 panic_on_taint &= TAINT_FLAGS_MAX;
908
909 if (!panic_on_taint)
910 return -EINVAL;
911
912 if (s && !strcmp(s, "nousertaint"))
913 panic_on_taint_nousertaint = true;
914
915 pr_info("panic_on_taint: bitmask=0x%lx nousertaint_mode=%s\n",
916 panic_on_taint, str_enabled_disabled(panic_on_taint_nousertaint));
917
918 return 0;
919}
920early_param("panic_on_taint", panic_on_taint_setup);
921

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source code of linux/kernel/panic.c