projects/linux·blob v6.17 · refs

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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Detect Hung Task
4 *
5 * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
6 *
7 */
8
9#include <linux/mm.h>
10#include <linux/cpu.h>
11#include <linux/nmi.h>
12#include <linux/init.h>
13#include <linux/delay.h>
14#include <linux/freezer.h>
15#include <linux/kthread.h>
16#include <linux/lockdep.h>
17#include <linux/export.h>
18#include <linux/panic_notifier.h>
19#include <linux/sysctl.h>
20#include <linux/suspend.h>
21#include <linux/utsname.h>
22#include <linux/sched/signal.h>
23#include <linux/sched/debug.h>
24#include <linux/sched/sysctl.h>
25#include <linux/hung_task.h>
26#include <linux/rwsem.h>
27
28#include <trace/events/sched.h>
29
30/*
31 * The number of tasks checked:
32 */
33static int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
34
35/*
36 * Total number of tasks detected as hung since boot:
37 */
38static unsigned long __read_mostly sysctl_hung_task_detect_count;
39
40/*
41 * Limit number of tasks checked in a batch.
42 *
43 * This value controls the preemptibility of khungtaskd since preemption
44 * is disabled during the critical section. It also controls the size of
45 * the RCU grace period. So it needs to be upper-bound.
46 */
47#define HUNG_TASK_LOCK_BREAK (HZ / 10)
48
49/*
50 * Zero means infinite timeout - no checking done:
51 */
52unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
53EXPORT_SYMBOL_GPL(sysctl_hung_task_timeout_secs);
54
55/*
56 * Zero (default value) means use sysctl_hung_task_timeout_secs:
57 */
58static unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
59
60static int __read_mostly sysctl_hung_task_warnings = 10;
61
62static int __read_mostly did_panic;
63static bool hung_task_show_lock;
64static bool hung_task_call_panic;
65static bool hung_task_show_all_bt;
66
67static struct task_struct *watchdog_task;
68
69#ifdef CONFIG_SMP
70/*
71 * Should we dump all CPUs backtraces in a hung task event?
72 * Defaults to 0, can be changed via sysctl.
73 */
74static unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
75#else
76#define sysctl_hung_task_all_cpu_backtrace 0
77#endif /* CONFIG_SMP */
78
79/*
80 * Should we panic (and reboot, if panic_timeout= is set) when a
81 * hung task is detected:
82 */
83static unsigned int __read_mostly sysctl_hung_task_panic =
84 IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC);
85
86static int
87hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
88{
89 did_panic = 1;
90
91 return NOTIFY_DONE;
92}
93
94static struct notifier_block panic_block = {
95 .notifier_call = hung_task_panic,
96};
97
98
99#ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER
100static void debug_show_blocker(struct task_struct *task)
101{
102 struct task_struct *g, *t;
103 unsigned long owner, blocker, blocker_type;
104 const char *rwsem_blocked_by, *rwsem_blocked_as;
105
106 RCU_LOCKDEP_WARN(!rcu_read_lock_held(), "No rcu lock held");
107
108 blocker = READ_ONCE(task->blocker);
109 if (!blocker)
110 return;
111
112 blocker_type = hung_task_get_blocker_type(blocker);
113
114 switch (blocker_type) {
115 case BLOCKER_TYPE_MUTEX:
116 owner = mutex_get_owner(hung_task_blocker_to_lock(blocker));
117 break;
118 case BLOCKER_TYPE_SEM:
119 owner = sem_last_holder(hung_task_blocker_to_lock(blocker));
120 break;
121 case BLOCKER_TYPE_RWSEM_READER:
122 case BLOCKER_TYPE_RWSEM_WRITER:
123 owner = (unsigned long)rwsem_owner(
124 hung_task_blocker_to_lock(blocker));
125 rwsem_blocked_as = (blocker_type == BLOCKER_TYPE_RWSEM_READER) ?
126 "reader" : "writer";
127 rwsem_blocked_by = is_rwsem_reader_owned(
128 hung_task_blocker_to_lock(blocker)) ?
129 "reader" : "writer";
130 break;
131 default:
132 WARN_ON_ONCE(1);
133 return;
134 }
135
136
137 if (unlikely(!owner)) {
138 switch (blocker_type) {
139 case BLOCKER_TYPE_MUTEX:
140 pr_err("INFO: task %s:%d is blocked on a mutex, but the owner is not found.\n",
141 task->comm, task->pid);
142 break;
143 case BLOCKER_TYPE_SEM:
144 pr_err("INFO: task %s:%d is blocked on a semaphore, but the last holder is not found.\n",
145 task->comm, task->pid);
146 break;
147 case BLOCKER_TYPE_RWSEM_READER:
148 case BLOCKER_TYPE_RWSEM_WRITER:
149 pr_err("INFO: task %s:%d is blocked on an rw-semaphore, but the owner is not found.\n",
150 task->comm, task->pid);
151 break;
152 }
153 return;
154 }
155
156 /* Ensure the owner information is correct. */
157 for_each_process_thread(g, t) {
158 if ((unsigned long)t != owner)
159 continue;
160
161 switch (blocker_type) {
162 case BLOCKER_TYPE_MUTEX:
163 pr_err("INFO: task %s:%d is blocked on a mutex likely owned by task %s:%d.\n",
164 task->comm, task->pid, t->comm, t->pid);
165 break;
166 case BLOCKER_TYPE_SEM:
167 pr_err("INFO: task %s:%d blocked on a semaphore likely last held by task %s:%d\n",
168 task->comm, task->pid, t->comm, t->pid);
169 break;
170 case BLOCKER_TYPE_RWSEM_READER:
171 case BLOCKER_TYPE_RWSEM_WRITER:
172 pr_err("INFO: task %s:%d <%s> blocked on an rw-semaphore likely owned by task %s:%d <%s>\n",
173 task->comm, task->pid, rwsem_blocked_as, t->comm,
174 t->pid, rwsem_blocked_by);
175 break;
176 }
177 sched_show_task(t);
178 return;
179 }
180}
181#else
182static inline void debug_show_blocker(struct task_struct *task)
183{
184}
185#endif
186
187static void check_hung_task(struct task_struct *t, unsigned long timeout)
188{
189 unsigned long switch_count = t->nvcsw + t->nivcsw;
190
191 /*
192 * Ensure the task is not frozen.
193 * Also, skip vfork and any other user process that freezer should skip.
194 */
195 if (unlikely(READ_ONCE(t->__state) & TASK_FROZEN))
196 return;
197
198 /*
199 * When a freshly created task is scheduled once, changes its state to
200 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
201 * musn't be checked.
202 */
203 if (unlikely(!switch_count))
204 return;
205
206 if (switch_count != t->last_switch_count) {
207 t->last_switch_count = switch_count;
208 t->last_switch_time = jiffies;
209 return;
210 }
211 if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
212 return;
213
214 /*
215 * This counter tracks the total number of tasks detected as hung
216 * since boot.
217 */
218 sysctl_hung_task_detect_count++;
219
220 trace_sched_process_hang(t);
221
222 if (sysctl_hung_task_panic) {
223 console_verbose();
224 hung_task_show_lock = true;
225 hung_task_call_panic = true;
226 }
227
228 /*
229 * Ok, the task did not get scheduled for more than 2 minutes,
230 * complain:
231 */
232 if (sysctl_hung_task_warnings || hung_task_call_panic) {
233 if (sysctl_hung_task_warnings > 0)
234 sysctl_hung_task_warnings--;
235 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
236 t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
237 pr_err(" %s %s %.*s\n",
238 print_tainted(), init_utsname()->release,
239 (int)strcspn(init_utsname()->version, " "),
240 init_utsname()->version);
241 if (t->flags & PF_POSTCOREDUMP)
242 pr_err(" Blocked by coredump.\n");
243 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
244 " disables this message.\n");
245 sched_show_task(t);
246 debug_show_blocker(t);
247 hung_task_show_lock = true;
248
249 if (sysctl_hung_task_all_cpu_backtrace)
250 hung_task_show_all_bt = true;
251 if (!sysctl_hung_task_warnings)
252 pr_info("Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings\n");
253 }
254
255 touch_nmi_watchdog();
256}
257
258/*
259 * To avoid extending the RCU grace period for an unbounded amount of time,
260 * periodically exit the critical section and enter a new one.
261 *
262 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
263 * to exit the grace period. For classic RCU, a reschedule is required.
264 */
265static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
266{
267 bool can_cont;
268
269 get_task_struct(g);
270 get_task_struct(t);
271 rcu_read_unlock();
272 cond_resched();
273 rcu_read_lock();
274 can_cont = pid_alive(g) && pid_alive(t);
275 put_task_struct(t);
276 put_task_struct(g);
277
278 return can_cont;
279}
280
281/*
282 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
283 * a really long time (120 seconds). If that happens, print out
284 * a warning.
285 */
286static void check_hung_uninterruptible_tasks(unsigned long timeout)
287{
288 int max_count = sysctl_hung_task_check_count;
289 unsigned long last_break = jiffies;
290 struct task_struct *g, *t;
291
292 /*
293 * If the system crashed already then all bets are off,
294 * do not report extra hung tasks:
295 */
296 if (test_taint(TAINT_DIE) || did_panic)
297 return;
298
299 hung_task_show_lock = false;
300 rcu_read_lock();
301 for_each_process_thread(g, t) {
302 unsigned int state;
303
304 if (!max_count--)
305 goto unlock;
306 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
307 if (!rcu_lock_break(g, t))
308 goto unlock;
309 last_break = jiffies;
310 }
311 /*
312 * skip the TASK_KILLABLE tasks -- these can be killed
313 * skip the TASK_IDLE tasks -- those are genuinely idle
314 */
315 state = READ_ONCE(t->__state);
316 if ((state & TASK_UNINTERRUPTIBLE) &&
317 !(state & TASK_WAKEKILL) &&
318 !(state & TASK_NOLOAD))
319 check_hung_task(t, timeout);
320 }
321 unlock:
322 rcu_read_unlock();
323 if (hung_task_show_lock)
324 debug_show_all_locks();
325
326 if (hung_task_show_all_bt) {
327 hung_task_show_all_bt = false;
328 trigger_all_cpu_backtrace();
329 }
330
331 if (hung_task_call_panic)
332 panic("hung_task: blocked tasks");
333}
334
335static long hung_timeout_jiffies(unsigned long last_checked,
336 unsigned long timeout)
337{
338 /* timeout of 0 will disable the watchdog */
339 return timeout ? last_checked - jiffies + timeout * HZ :
340 MAX_SCHEDULE_TIMEOUT;
341}
342
343#ifdef CONFIG_SYSCTL
344/*
345 * Process updating of timeout sysctl
346 */
347static int proc_dohung_task_timeout_secs(const struct ctl_table *table, int write,
348 void *buffer,
349 size_t *lenp, loff_t *ppos)
350{
351 int ret;
352
353 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
354
355 if (ret || !write)
356 goto out;
357
358 wake_up_process(watchdog_task);
359
360 out:
361 return ret;
362}
363
364/*
365 * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs
366 * and hung_task_check_interval_secs
367 */
368static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ);
369static const struct ctl_table hung_task_sysctls[] = {
370#ifdef CONFIG_SMP
371 {
372 .procname = "hung_task_all_cpu_backtrace",
373 .data = &sysctl_hung_task_all_cpu_backtrace,
374 .maxlen = sizeof(int),
375 .mode = 0644,
376 .proc_handler = proc_dointvec_minmax,
377 .extra1 = SYSCTL_ZERO,
378 .extra2 = SYSCTL_ONE,
379 },
380#endif /* CONFIG_SMP */
381 {
382 .procname = "hung_task_panic",
383 .data = &sysctl_hung_task_panic,
384 .maxlen = sizeof(int),
385 .mode = 0644,
386 .proc_handler = proc_dointvec_minmax,
387 .extra1 = SYSCTL_ZERO,
388 .extra2 = SYSCTL_ONE,
389 },
390 {
391 .procname = "hung_task_check_count",
392 .data = &sysctl_hung_task_check_count,
393 .maxlen = sizeof(int),
394 .mode = 0644,
395 .proc_handler = proc_dointvec_minmax,
396 .extra1 = SYSCTL_ZERO,
397 },
398 {
399 .procname = "hung_task_timeout_secs",
400 .data = &sysctl_hung_task_timeout_secs,
401 .maxlen = sizeof(unsigned long),
402 .mode = 0644,
403 .proc_handler = proc_dohung_task_timeout_secs,
404 .extra2 = (void *)&hung_task_timeout_max,
405 },
406 {
407 .procname = "hung_task_check_interval_secs",
408 .data = &sysctl_hung_task_check_interval_secs,
409 .maxlen = sizeof(unsigned long),
410 .mode = 0644,
411 .proc_handler = proc_dohung_task_timeout_secs,
412 .extra2 = (void *)&hung_task_timeout_max,
413 },
414 {
415 .procname = "hung_task_warnings",
416 .data = &sysctl_hung_task_warnings,
417 .maxlen = sizeof(int),
418 .mode = 0644,
419 .proc_handler = proc_dointvec_minmax,
420 .extra1 = SYSCTL_NEG_ONE,
421 },
422 {
423 .procname = "hung_task_detect_count",
424 .data = &sysctl_hung_task_detect_count,
425 .maxlen = sizeof(unsigned long),
426 .mode = 0444,
427 .proc_handler = proc_doulongvec_minmax,
428 },
429};
430
431static void __init hung_task_sysctl_init(void)
432{
433 register_sysctl_init("kernel", hung_task_sysctls);
434}
435#else
436#define hung_task_sysctl_init() do { } while (0)
437#endif /* CONFIG_SYSCTL */
438
439
440static atomic_t reset_hung_task = ATOMIC_INIT(0);
441
442void reset_hung_task_detector(void)
443{
444 atomic_set(&reset_hung_task, 1);
445}
446EXPORT_SYMBOL_GPL(reset_hung_task_detector);
447
448static bool hung_detector_suspended;
449
450static int hungtask_pm_notify(struct notifier_block *self,
451 unsigned long action, void *hcpu)
452{
453 switch (action) {
454 case PM_SUSPEND_PREPARE:
455 case PM_HIBERNATION_PREPARE:
456 case PM_RESTORE_PREPARE:
457 hung_detector_suspended = true;
458 break;
459 case PM_POST_SUSPEND:
460 case PM_POST_HIBERNATION:
461 case PM_POST_RESTORE:
462 hung_detector_suspended = false;
463 break;
464 default:
465 break;
466 }
467 return NOTIFY_OK;
468}
469
470/*
471 * kthread which checks for tasks stuck in D state
472 */
473static int watchdog(void *dummy)
474{
475 unsigned long hung_last_checked = jiffies;
476
477 set_user_nice(current, 0);
478
479 for ( ; ; ) {
480 unsigned long timeout = sysctl_hung_task_timeout_secs;
481 unsigned long interval = sysctl_hung_task_check_interval_secs;
482 long t;
483
484 if (interval == 0)
485 interval = timeout;
486 interval = min_t(unsigned long, interval, timeout);
487 t = hung_timeout_jiffies(hung_last_checked, interval);
488 if (t <= 0) {
489 if (!atomic_xchg(&reset_hung_task, 0) &&
490 !hung_detector_suspended)
491 check_hung_uninterruptible_tasks(timeout);
492 hung_last_checked = jiffies;
493 continue;
494 }
495 schedule_timeout_interruptible(t);
496 }
497
498 return 0;
499}
500
501static int __init hung_task_init(void)
502{
503 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
504
505 /* Disable hung task detector on suspend */
506 pm_notifier(hungtask_pm_notify, 0);
507
508 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
509 hung_task_sysctl_init();
510
511 return 0;
512}
513subsys_initcall(hung_task_init);