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v4.17
 
  1/*
  2 * Detect Hung Task
  3 *
  4 * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
  5 *
  6 */
  7
  8#include <linux/mm.h>
  9#include <linux/cpu.h>
 10#include <linux/nmi.h>
 11#include <linux/init.h>
 12#include <linux/delay.h>
 13#include <linux/freezer.h>
 14#include <linux/kthread.h>
 15#include <linux/lockdep.h>
 16#include <linux/export.h>
 
 17#include <linux/sysctl.h>
 
 18#include <linux/utsname.h>
 19#include <linux/sched/signal.h>
 20#include <linux/sched/debug.h>
 
 21
 22#include <trace/events/sched.h>
 23
 24/*
 25 * The number of tasks checked:
 26 */
 27int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
 28
 29/*
 30 * Limit number of tasks checked in a batch.
 31 *
 32 * This value controls the preemptibility of khungtaskd since preemption
 33 * is disabled during the critical section. It also controls the size of
 34 * the RCU grace period. So it needs to be upper-bound.
 35 */
 36#define HUNG_TASK_BATCHING 1024
 37
 38/*
 39 * Zero means infinite timeout - no checking done:
 40 */
 41unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
 
 42
 43int __read_mostly sysctl_hung_task_warnings = 10;
 
 
 
 
 
 44
 45static int __read_mostly did_panic;
 46static bool hung_task_show_lock;
 
 
 47
 48static struct task_struct *watchdog_task;
 49
 
 
 
 
 
 
 
 
 
 
 50/*
 51 * Should we panic (and reboot, if panic_timeout= is set) when a
 52 * hung task is detected:
 53 */
 54unsigned int __read_mostly sysctl_hung_task_panic =
 55				CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
 56
 57static int __init hung_task_panic_setup(char *str)
 58{
 59	int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
 60
 61	if (rc)
 62		return rc;
 63	return 1;
 64}
 65__setup("hung_task_panic=", hung_task_panic_setup);
 66
 67static int
 68hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
 69{
 70	did_panic = 1;
 71
 72	return NOTIFY_DONE;
 73}
 74
 75static struct notifier_block panic_block = {
 76	.notifier_call = hung_task_panic,
 77};
 78
 79static void check_hung_task(struct task_struct *t, unsigned long timeout)
 80{
 81	unsigned long switch_count = t->nvcsw + t->nivcsw;
 82
 83	/*
 84	 * Ensure the task is not frozen.
 85	 * Also, skip vfork and any other user process that freezer should skip.
 86	 */
 87	if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
 88	    return;
 89
 90	/*
 91	 * When a freshly created task is scheduled once, changes its state to
 92	 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
 93	 * musn't be checked.
 94	 */
 95	if (unlikely(!switch_count))
 96		return;
 97
 98	if (switch_count != t->last_switch_count) {
 99		t->last_switch_count = switch_count;
 
100		return;
101	}
 
 
102
103	trace_sched_process_hang(t);
104
105	if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic)
106		return;
 
 
 
107
108	/*
109	 * Ok, the task did not get scheduled for more than 2 minutes,
110	 * complain:
111	 */
112	if (sysctl_hung_task_warnings) {
113		if (sysctl_hung_task_warnings > 0)
114			sysctl_hung_task_warnings--;
115		pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
116			t->comm, t->pid, timeout);
117		pr_err("      %s %s %.*s\n",
118			print_tainted(), init_utsname()->release,
119			(int)strcspn(init_utsname()->version, " "),
120			init_utsname()->version);
121		pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
122			" disables this message.\n");
123		sched_show_task(t);
124		hung_task_show_lock = true;
 
 
 
 
 
125	}
126
127	touch_nmi_watchdog();
128
129	if (sysctl_hung_task_panic) {
130		if (hung_task_show_lock)
131			debug_show_all_locks();
132		trigger_all_cpu_backtrace();
133		panic("hung_task: blocked tasks");
134	}
135}
136
137/*
138 * To avoid extending the RCU grace period for an unbounded amount of time,
139 * periodically exit the critical section and enter a new one.
140 *
141 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
142 * to exit the grace period. For classic RCU, a reschedule is required.
143 */
144static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
145{
146	bool can_cont;
147
148	get_task_struct(g);
149	get_task_struct(t);
150	rcu_read_unlock();
151	cond_resched();
152	rcu_read_lock();
153	can_cont = pid_alive(g) && pid_alive(t);
154	put_task_struct(t);
155	put_task_struct(g);
156
157	return can_cont;
158}
159
160/*
161 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
162 * a really long time (120 seconds). If that happens, print out
163 * a warning.
164 */
165static void check_hung_uninterruptible_tasks(unsigned long timeout)
166{
167	int max_count = sysctl_hung_task_check_count;
168	int batch_count = HUNG_TASK_BATCHING;
169	struct task_struct *g, *t;
170
171	/*
172	 * If the system crashed already then all bets are off,
173	 * do not report extra hung tasks:
174	 */
175	if (test_taint(TAINT_DIE) || did_panic)
176		return;
177
178	hung_task_show_lock = false;
179	rcu_read_lock();
180	for_each_process_thread(g, t) {
 
 
181		if (!max_count--)
182			goto unlock;
183		if (!--batch_count) {
184			batch_count = HUNG_TASK_BATCHING;
185			if (!rcu_lock_break(g, t))
186				goto unlock;
 
187		}
188		/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
189		if (t->state == TASK_UNINTERRUPTIBLE)
 
 
 
 
 
 
190			check_hung_task(t, timeout);
191	}
192 unlock:
193	rcu_read_unlock();
194	if (hung_task_show_lock)
195		debug_show_all_locks();
 
 
 
 
 
 
 
 
196}
197
198static long hung_timeout_jiffies(unsigned long last_checked,
199				 unsigned long timeout)
200{
201	/* timeout of 0 will disable the watchdog */
202	return timeout ? last_checked - jiffies + timeout * HZ :
203		MAX_SCHEDULE_TIMEOUT;
204}
205
 
206/*
207 * Process updating of timeout sysctl
208 */
209int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
210				  void __user *buffer,
211				  size_t *lenp, loff_t *ppos)
212{
213	int ret;
214
215	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
216
217	if (ret || !write)
218		goto out;
219
220	wake_up_process(watchdog_task);
221
222 out:
223	return ret;
224}
225
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
226static atomic_t reset_hung_task = ATOMIC_INIT(0);
227
228void reset_hung_task_detector(void)
229{
230	atomic_set(&reset_hung_task, 1);
231}
232EXPORT_SYMBOL_GPL(reset_hung_task_detector);
233
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
234/*
235 * kthread which checks for tasks stuck in D state
236 */
237static int watchdog(void *dummy)
238{
239	unsigned long hung_last_checked = jiffies;
240
241	set_user_nice(current, 0);
242
243	for ( ; ; ) {
244		unsigned long timeout = sysctl_hung_task_timeout_secs;
245		long t = hung_timeout_jiffies(hung_last_checked, timeout);
 
246
 
 
 
 
247		if (t <= 0) {
248			if (!atomic_xchg(&reset_hung_task, 0))
 
249				check_hung_uninterruptible_tasks(timeout);
250			hung_last_checked = jiffies;
251			continue;
252		}
253		schedule_timeout_interruptible(t);
254	}
255
256	return 0;
257}
258
259static int __init hung_task_init(void)
260{
261	atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 
 
 
 
262	watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 
263
264	return 0;
265}
266subsys_initcall(hung_task_init);
v6.9.4
  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
 26#include <trace/events/sched.h>
 27
 28/*
 29 * The number of tasks checked:
 30 */
 31static int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
 32
 33/*
 34 * Limit number of tasks checked in a batch.
 35 *
 36 * This value controls the preemptibility of khungtaskd since preemption
 37 * is disabled during the critical section. It also controls the size of
 38 * the RCU grace period. So it needs to be upper-bound.
 39 */
 40#define HUNG_TASK_LOCK_BREAK (HZ / 10)
 41
 42/*
 43 * Zero means infinite timeout - no checking done:
 44 */
 45unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
 46EXPORT_SYMBOL_GPL(sysctl_hung_task_timeout_secs);
 47
 48/*
 49 * Zero (default value) means use sysctl_hung_task_timeout_secs:
 50 */
 51static unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
 52
 53static int __read_mostly sysctl_hung_task_warnings = 10;
 54
 55static int __read_mostly did_panic;
 56static bool hung_task_show_lock;
 57static bool hung_task_call_panic;
 58static bool hung_task_show_all_bt;
 59
 60static struct task_struct *watchdog_task;
 61
 62#ifdef CONFIG_SMP
 63/*
 64 * Should we dump all CPUs backtraces in a hung task event?
 65 * Defaults to 0, can be changed via sysctl.
 66 */
 67static unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
 68#else
 69#define sysctl_hung_task_all_cpu_backtrace 0
 70#endif /* CONFIG_SMP */
 71
 72/*
 73 * Should we panic (and reboot, if panic_timeout= is set) when a
 74 * hung task is detected:
 75 */
 76static unsigned int __read_mostly sysctl_hung_task_panic =
 77	IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC);
 
 
 
 
 
 
 
 
 
 
 78
 79static int
 80hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
 81{
 82	did_panic = 1;
 83
 84	return NOTIFY_DONE;
 85}
 86
 87static struct notifier_block panic_block = {
 88	.notifier_call = hung_task_panic,
 89};
 90
 91static void check_hung_task(struct task_struct *t, unsigned long timeout)
 92{
 93	unsigned long switch_count = t->nvcsw + t->nivcsw;
 94
 95	/*
 96	 * Ensure the task is not frozen.
 97	 * Also, skip vfork and any other user process that freezer should skip.
 98	 */
 99	if (unlikely(READ_ONCE(t->__state) & TASK_FROZEN))
100		return;
101
102	/*
103	 * When a freshly created task is scheduled once, changes its state to
104	 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
105	 * musn't be checked.
106	 */
107	if (unlikely(!switch_count))
108		return;
109
110	if (switch_count != t->last_switch_count) {
111		t->last_switch_count = switch_count;
112		t->last_switch_time = jiffies;
113		return;
114	}
115	if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
116		return;
117
118	trace_sched_process_hang(t);
119
120	if (sysctl_hung_task_panic) {
121		console_verbose();
122		hung_task_show_lock = true;
123		hung_task_call_panic = true;
124	}
125
126	/*
127	 * Ok, the task did not get scheduled for more than 2 minutes,
128	 * complain:
129	 */
130	if (sysctl_hung_task_warnings) {
131		if (sysctl_hung_task_warnings > 0)
132			sysctl_hung_task_warnings--;
133		pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
134		       t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
135		pr_err("      %s %s %.*s\n",
136			print_tainted(), init_utsname()->release,
137			(int)strcspn(init_utsname()->version, " "),
138			init_utsname()->version);
139		pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
140			" disables this message.\n");
141		sched_show_task(t);
142		hung_task_show_lock = true;
143
144		if (sysctl_hung_task_all_cpu_backtrace)
145			hung_task_show_all_bt = true;
146		if (!sysctl_hung_task_warnings)
147			pr_info("Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings\n");
148	}
149
150	touch_nmi_watchdog();
 
 
 
 
 
 
 
151}
152
153/*
154 * To avoid extending the RCU grace period for an unbounded amount of time,
155 * periodically exit the critical section and enter a new one.
156 *
157 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
158 * to exit the grace period. For classic RCU, a reschedule is required.
159 */
160static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
161{
162	bool can_cont;
163
164	get_task_struct(g);
165	get_task_struct(t);
166	rcu_read_unlock();
167	cond_resched();
168	rcu_read_lock();
169	can_cont = pid_alive(g) && pid_alive(t);
170	put_task_struct(t);
171	put_task_struct(g);
172
173	return can_cont;
174}
175
176/*
177 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
178 * a really long time (120 seconds). If that happens, print out
179 * a warning.
180 */
181static void check_hung_uninterruptible_tasks(unsigned long timeout)
182{
183	int max_count = sysctl_hung_task_check_count;
184	unsigned long last_break = jiffies;
185	struct task_struct *g, *t;
186
187	/*
188	 * If the system crashed already then all bets are off,
189	 * do not report extra hung tasks:
190	 */
191	if (test_taint(TAINT_DIE) || did_panic)
192		return;
193
194	hung_task_show_lock = false;
195	rcu_read_lock();
196	for_each_process_thread(g, t) {
197		unsigned int state;
198
199		if (!max_count--)
200			goto unlock;
201		if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
 
202			if (!rcu_lock_break(g, t))
203				goto unlock;
204			last_break = jiffies;
205		}
206		/*
207		 * skip the TASK_KILLABLE tasks -- these can be killed
208		 * skip the TASK_IDLE tasks -- those are genuinely idle
209		 */
210		state = READ_ONCE(t->__state);
211		if ((state & TASK_UNINTERRUPTIBLE) &&
212		    !(state & TASK_WAKEKILL) &&
213		    !(state & TASK_NOLOAD))
214			check_hung_task(t, timeout);
215	}
216 unlock:
217	rcu_read_unlock();
218	if (hung_task_show_lock)
219		debug_show_all_locks();
220
221	if (hung_task_show_all_bt) {
222		hung_task_show_all_bt = false;
223		trigger_all_cpu_backtrace();
224	}
225
226	if (hung_task_call_panic)
227		panic("hung_task: blocked tasks");
228}
229
230static long hung_timeout_jiffies(unsigned long last_checked,
231				 unsigned long timeout)
232{
233	/* timeout of 0 will disable the watchdog */
234	return timeout ? last_checked - jiffies + timeout * HZ :
235		MAX_SCHEDULE_TIMEOUT;
236}
237
238#ifdef CONFIG_SYSCTL
239/*
240 * Process updating of timeout sysctl
241 */
242static int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
243				  void *buffer,
244				  size_t *lenp, loff_t *ppos)
245{
246	int ret;
247
248	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
249
250	if (ret || !write)
251		goto out;
252
253	wake_up_process(watchdog_task);
254
255 out:
256	return ret;
257}
258
259/*
260 * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs
261 * and hung_task_check_interval_secs
262 */
263static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ);
264static struct ctl_table hung_task_sysctls[] = {
265#ifdef CONFIG_SMP
266	{
267		.procname	= "hung_task_all_cpu_backtrace",
268		.data		= &sysctl_hung_task_all_cpu_backtrace,
269		.maxlen		= sizeof(int),
270		.mode		= 0644,
271		.proc_handler	= proc_dointvec_minmax,
272		.extra1		= SYSCTL_ZERO,
273		.extra2		= SYSCTL_ONE,
274	},
275#endif /* CONFIG_SMP */
276	{
277		.procname	= "hung_task_panic",
278		.data		= &sysctl_hung_task_panic,
279		.maxlen		= sizeof(int),
280		.mode		= 0644,
281		.proc_handler	= proc_dointvec_minmax,
282		.extra1		= SYSCTL_ZERO,
283		.extra2		= SYSCTL_ONE,
284	},
285	{
286		.procname	= "hung_task_check_count",
287		.data		= &sysctl_hung_task_check_count,
288		.maxlen		= sizeof(int),
289		.mode		= 0644,
290		.proc_handler	= proc_dointvec_minmax,
291		.extra1		= SYSCTL_ZERO,
292	},
293	{
294		.procname	= "hung_task_timeout_secs",
295		.data		= &sysctl_hung_task_timeout_secs,
296		.maxlen		= sizeof(unsigned long),
297		.mode		= 0644,
298		.proc_handler	= proc_dohung_task_timeout_secs,
299		.extra2		= (void *)&hung_task_timeout_max,
300	},
301	{
302		.procname	= "hung_task_check_interval_secs",
303		.data		= &sysctl_hung_task_check_interval_secs,
304		.maxlen		= sizeof(unsigned long),
305		.mode		= 0644,
306		.proc_handler	= proc_dohung_task_timeout_secs,
307		.extra2		= (void *)&hung_task_timeout_max,
308	},
309	{
310		.procname	= "hung_task_warnings",
311		.data		= &sysctl_hung_task_warnings,
312		.maxlen		= sizeof(int),
313		.mode		= 0644,
314		.proc_handler	= proc_dointvec_minmax,
315		.extra1		= SYSCTL_NEG_ONE,
316	},
317	{}
318};
319
320static void __init hung_task_sysctl_init(void)
321{
322	register_sysctl_init("kernel", hung_task_sysctls);
323}
324#else
325#define hung_task_sysctl_init() do { } while (0)
326#endif /* CONFIG_SYSCTL */
327
328
329static atomic_t reset_hung_task = ATOMIC_INIT(0);
330
331void reset_hung_task_detector(void)
332{
333	atomic_set(&reset_hung_task, 1);
334}
335EXPORT_SYMBOL_GPL(reset_hung_task_detector);
336
337static bool hung_detector_suspended;
338
339static int hungtask_pm_notify(struct notifier_block *self,
340			      unsigned long action, void *hcpu)
341{
342	switch (action) {
343	case PM_SUSPEND_PREPARE:
344	case PM_HIBERNATION_PREPARE:
345	case PM_RESTORE_PREPARE:
346		hung_detector_suspended = true;
347		break;
348	case PM_POST_SUSPEND:
349	case PM_POST_HIBERNATION:
350	case PM_POST_RESTORE:
351		hung_detector_suspended = false;
352		break;
353	default:
354		break;
355	}
356	return NOTIFY_OK;
357}
358
359/*
360 * kthread which checks for tasks stuck in D state
361 */
362static int watchdog(void *dummy)
363{
364	unsigned long hung_last_checked = jiffies;
365
366	set_user_nice(current, 0);
367
368	for ( ; ; ) {
369		unsigned long timeout = sysctl_hung_task_timeout_secs;
370		unsigned long interval = sysctl_hung_task_check_interval_secs;
371		long t;
372
373		if (interval == 0)
374			interval = timeout;
375		interval = min_t(unsigned long, interval, timeout);
376		t = hung_timeout_jiffies(hung_last_checked, interval);
377		if (t <= 0) {
378			if (!atomic_xchg(&reset_hung_task, 0) &&
379			    !hung_detector_suspended)
380				check_hung_uninterruptible_tasks(timeout);
381			hung_last_checked = jiffies;
382			continue;
383		}
384		schedule_timeout_interruptible(t);
385	}
386
387	return 0;
388}
389
390static int __init hung_task_init(void)
391{
392	atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
393
394	/* Disable hung task detector on suspend */
395	pm_notifier(hungtask_pm_notify, 0);
396
397	watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
398	hung_task_sysctl_init();
399
400	return 0;
401}
402subsys_initcall(hung_task_init);