4 * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
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>
22 #include <trace/events/sched.h>
25 * The number of tasks checked:
27 int __read_mostly sysctl_hung_task_check_count
= PID_MAX_LIMIT
;
30 * Limit number of tasks checked in a batch.
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.
36 #define HUNG_TASK_LOCK_BREAK (HZ / 10)
39 * Zero means infinite timeout - no checking done:
41 unsigned long __read_mostly sysctl_hung_task_timeout_secs
= CONFIG_DEFAULT_HUNG_TASK_TIMEOUT
;
43 int __read_mostly sysctl_hung_task_warnings
= 10;
45 static int __read_mostly did_panic
;
46 static bool hung_task_show_lock
;
47 static bool hung_task_call_panic
;
49 static struct task_struct
*watchdog_task
;
52 * Should we panic (and reboot, if panic_timeout= is set) when a
53 * hung task is detected:
55 unsigned int __read_mostly sysctl_hung_task_panic
=
56 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE
;
58 static int __init
hung_task_panic_setup(char *str
)
60 int rc
= kstrtouint(str
, 0, &sysctl_hung_task_panic
);
66 __setup("hung_task_panic=", hung_task_panic_setup
);
69 hung_task_panic(struct notifier_block
*this, unsigned long event
, void *ptr
)
76 static struct notifier_block panic_block
= {
77 .notifier_call
= hung_task_panic
,
80 static void check_hung_task(struct task_struct
*t
, unsigned long timeout
)
82 unsigned long switch_count
= t
->nvcsw
+ t
->nivcsw
;
85 * Ensure the task is not frozen.
86 * Also, skip vfork and any other user process that freezer should skip.
88 if (unlikely(t
->flags
& (PF_FROZEN
| PF_FREEZER_SKIP
)))
92 * When a freshly created task is scheduled once, changes its state to
93 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
96 if (unlikely(!switch_count
))
99 if (switch_count
!= t
->last_switch_count
) {
100 t
->last_switch_count
= switch_count
;
104 trace_sched_process_hang(t
);
106 if (sysctl_hung_task_panic
) {
108 hung_task_show_lock
= true;
109 hung_task_call_panic
= true;
113 * Ok, the task did not get scheduled for more than 2 minutes,
116 if (sysctl_hung_task_warnings
) {
117 if (sysctl_hung_task_warnings
> 0)
118 sysctl_hung_task_warnings
--;
119 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
120 t
->comm
, t
->pid
, timeout
);
121 pr_err(" %s %s %.*s\n",
122 print_tainted(), init_utsname()->release
,
123 (int)strcspn(init_utsname()->version
, " "),
124 init_utsname()->version
);
125 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
126 " disables this message.\n");
128 hung_task_show_lock
= true;
131 touch_nmi_watchdog();
135 * To avoid extending the RCU grace period for an unbounded amount of time,
136 * periodically exit the critical section and enter a new one.
138 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
139 * to exit the grace period. For classic RCU, a reschedule is required.
141 static bool rcu_lock_break(struct task_struct
*g
, struct task_struct
*t
)
150 can_cont
= pid_alive(g
) && pid_alive(t
);
158 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
159 * a really long time (120 seconds). If that happens, print out
162 static void check_hung_uninterruptible_tasks(unsigned long timeout
)
164 int max_count
= sysctl_hung_task_check_count
;
165 unsigned long last_break
= jiffies
;
166 struct task_struct
*g
, *t
;
169 * If the system crashed already then all bets are off,
170 * do not report extra hung tasks:
172 if (test_taint(TAINT_DIE
) || did_panic
)
175 hung_task_show_lock
= false;
177 for_each_process_thread(g
, t
) {
180 if (time_after(jiffies
, last_break
+ HUNG_TASK_LOCK_BREAK
)) {
181 if (!rcu_lock_break(g
, t
))
183 last_break
= jiffies
;
185 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
186 if (t
->state
== TASK_UNINTERRUPTIBLE
)
187 check_hung_task(t
, timeout
);
191 if (hung_task_show_lock
)
192 debug_show_all_locks();
193 if (hung_task_call_panic
) {
194 trigger_all_cpu_backtrace();
195 panic("hung_task: blocked tasks");
199 static long hung_timeout_jiffies(unsigned long last_checked
,
200 unsigned long timeout
)
202 /* timeout of 0 will disable the watchdog */
203 return timeout
? last_checked
- jiffies
+ timeout
* HZ
:
204 MAX_SCHEDULE_TIMEOUT
;
208 * Process updating of timeout sysctl
210 int proc_dohung_task_timeout_secs(struct ctl_table
*table
, int write
,
212 size_t *lenp
, loff_t
*ppos
)
216 ret
= proc_doulongvec_minmax(table
, write
, buffer
, lenp
, ppos
);
221 wake_up_process(watchdog_task
);
227 static atomic_t reset_hung_task
= ATOMIC_INIT(0);
229 void reset_hung_task_detector(void)
231 atomic_set(&reset_hung_task
, 1);
233 EXPORT_SYMBOL_GPL(reset_hung_task_detector
);
236 * kthread which checks for tasks stuck in D state
238 static int watchdog(void *dummy
)
240 unsigned long hung_last_checked
= jiffies
;
242 set_user_nice(current
, 0);
245 unsigned long timeout
= sysctl_hung_task_timeout_secs
;
246 long t
= hung_timeout_jiffies(hung_last_checked
, timeout
);
249 if (!atomic_xchg(&reset_hung_task
, 0))
250 check_hung_uninterruptible_tasks(timeout
);
251 hung_last_checked
= jiffies
;
254 schedule_timeout_interruptible(t
);
260 static int __init
hung_task_init(void)
262 atomic_notifier_chain_register(&panic_notifier_list
, &panic_block
);
263 watchdog_task
= kthread_run(watchdog
, NULL
, "khungtaskd");
267 subsys_initcall(hung_task_init
);