1 // SPDX-License-Identifier: GPL-2.0-only
5 * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
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>
26 #include <trace/events/sched.h>
29 * The number of tasks checked:
31 int __read_mostly sysctl_hung_task_check_count
= PID_MAX_LIMIT
;
34 * Limit number of tasks checked in a batch.
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.
40 #define HUNG_TASK_LOCK_BREAK (HZ / 10)
43 * Zero means infinite timeout - no checking done:
45 unsigned long __read_mostly sysctl_hung_task_timeout_secs
= CONFIG_DEFAULT_HUNG_TASK_TIMEOUT
;
48 * Zero (default value) means use sysctl_hung_task_timeout_secs:
50 unsigned long __read_mostly sysctl_hung_task_check_interval_secs
;
52 int __read_mostly sysctl_hung_task_warnings
= 10;
54 static int __read_mostly did_panic
;
55 static bool hung_task_show_lock
;
56 static bool hung_task_call_panic
;
57 static bool hung_task_show_all_bt
;
59 static struct task_struct
*watchdog_task
;
63 * Should we dump all CPUs backtraces in a hung task event?
64 * Defaults to 0, can be changed via sysctl.
66 unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace
;
67 #endif /* CONFIG_SMP */
70 * Should we panic (and reboot, if panic_timeout= is set) when a
71 * hung task is detected:
73 unsigned int __read_mostly sysctl_hung_task_panic
=
74 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE
;
77 hung_task_panic(struct notifier_block
*this, unsigned long event
, void *ptr
)
84 static struct notifier_block panic_block
= {
85 .notifier_call
= hung_task_panic
,
88 static void check_hung_task(struct task_struct
*t
, unsigned long timeout
)
90 unsigned long switch_count
= t
->nvcsw
+ t
->nivcsw
;
93 * Ensure the task is not frozen.
94 * Also, skip vfork and any other user process that freezer should skip.
96 if (unlikely(t
->flags
& (PF_FROZEN
| PF_FREEZER_SKIP
)))
100 * When a freshly created task is scheduled once, changes its state to
101 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
104 if (unlikely(!switch_count
))
107 if (switch_count
!= t
->last_switch_count
) {
108 t
->last_switch_count
= switch_count
;
109 t
->last_switch_time
= jiffies
;
112 if (time_is_after_jiffies(t
->last_switch_time
+ timeout
* HZ
))
115 trace_sched_process_hang(t
);
117 if (sysctl_hung_task_panic
) {
119 hung_task_show_lock
= true;
120 hung_task_call_panic
= true;
124 * Ok, the task did not get scheduled for more than 2 minutes,
127 if (sysctl_hung_task_warnings
) {
128 if (sysctl_hung_task_warnings
> 0)
129 sysctl_hung_task_warnings
--;
130 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
131 t
->comm
, t
->pid
, (jiffies
- t
->last_switch_time
) / HZ
);
132 pr_err(" %s %s %.*s\n",
133 print_tainted(), init_utsname()->release
,
134 (int)strcspn(init_utsname()->version
, " "),
135 init_utsname()->version
);
136 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
137 " disables this message.\n");
139 hung_task_show_lock
= true;
141 if (sysctl_hung_task_all_cpu_backtrace
)
142 hung_task_show_all_bt
= true;
145 touch_nmi_watchdog();
149 * To avoid extending the RCU grace period for an unbounded amount of time,
150 * periodically exit the critical section and enter a new one.
152 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
153 * to exit the grace period. For classic RCU, a reschedule is required.
155 static bool rcu_lock_break(struct task_struct
*g
, struct task_struct
*t
)
164 can_cont
= pid_alive(g
) && pid_alive(t
);
172 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
173 * a really long time (120 seconds). If that happens, print out
176 static void check_hung_uninterruptible_tasks(unsigned long timeout
)
178 int max_count
= sysctl_hung_task_check_count
;
179 unsigned long last_break
= jiffies
;
180 struct task_struct
*g
, *t
;
183 * If the system crashed already then all bets are off,
184 * do not report extra hung tasks:
186 if (test_taint(TAINT_DIE
) || did_panic
)
189 hung_task_show_lock
= false;
191 for_each_process_thread(g
, t
) {
194 if (time_after(jiffies
, last_break
+ HUNG_TASK_LOCK_BREAK
)) {
195 if (!rcu_lock_break(g
, t
))
197 last_break
= jiffies
;
199 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
200 if (READ_ONCE(t
->__state
) == TASK_UNINTERRUPTIBLE
)
201 check_hung_task(t
, timeout
);
205 if (hung_task_show_lock
)
206 debug_show_all_locks();
208 if (hung_task_show_all_bt
) {
209 hung_task_show_all_bt
= false;
210 trigger_all_cpu_backtrace();
213 if (hung_task_call_panic
)
214 panic("hung_task: blocked tasks");
217 static long hung_timeout_jiffies(unsigned long last_checked
,
218 unsigned long timeout
)
220 /* timeout of 0 will disable the watchdog */
221 return timeout
? last_checked
- jiffies
+ timeout
* HZ
:
222 MAX_SCHEDULE_TIMEOUT
;
226 * Process updating of timeout sysctl
228 int proc_dohung_task_timeout_secs(struct ctl_table
*table
, int write
,
229 void *buffer
, size_t *lenp
, loff_t
*ppos
)
233 ret
= proc_doulongvec_minmax(table
, write
, buffer
, lenp
, ppos
);
238 wake_up_process(watchdog_task
);
244 static atomic_t reset_hung_task
= ATOMIC_INIT(0);
246 void reset_hung_task_detector(void)
248 atomic_set(&reset_hung_task
, 1);
250 EXPORT_SYMBOL_GPL(reset_hung_task_detector
);
252 static bool hung_detector_suspended
;
254 static int hungtask_pm_notify(struct notifier_block
*self
,
255 unsigned long action
, void *hcpu
)
258 case PM_SUSPEND_PREPARE
:
259 case PM_HIBERNATION_PREPARE
:
260 case PM_RESTORE_PREPARE
:
261 hung_detector_suspended
= true;
263 case PM_POST_SUSPEND
:
264 case PM_POST_HIBERNATION
:
265 case PM_POST_RESTORE
:
266 hung_detector_suspended
= false;
275 * kthread which checks for tasks stuck in D state
277 static int watchdog(void *dummy
)
279 unsigned long hung_last_checked
= jiffies
;
281 set_user_nice(current
, 0);
284 unsigned long timeout
= sysctl_hung_task_timeout_secs
;
285 unsigned long interval
= sysctl_hung_task_check_interval_secs
;
290 interval
= min_t(unsigned long, interval
, timeout
);
291 t
= hung_timeout_jiffies(hung_last_checked
, interval
);
293 if (!atomic_xchg(&reset_hung_task
, 0) &&
294 !hung_detector_suspended
)
295 check_hung_uninterruptible_tasks(timeout
);
296 hung_last_checked
= jiffies
;
299 schedule_timeout_interruptible(t
);
305 static int __init
hung_task_init(void)
307 atomic_notifier_chain_register(&panic_notifier_list
, &panic_block
);
309 /* Disable hung task detector on suspend */
310 pm_notifier(hungtask_pm_notify
, 0);
312 watchdog_task
= kthread_run(watchdog
, NULL
, "khungtaskd");
316 subsys_initcall(hung_task_init
);