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_BATCHING 1024
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_warnings
&& !sysctl_hung_task_panic
)
110 * Ok, the task did not get scheduled for more than 2 minutes,
113 if (sysctl_hung_task_warnings
) {
114 if (sysctl_hung_task_warnings
> 0)
115 sysctl_hung_task_warnings
--;
116 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
117 t
->comm
, t
->pid
, timeout
);
118 pr_err(" %s %s %.*s\n",
119 print_tainted(), init_utsname()->release
,
120 (int)strcspn(init_utsname()->version
, " "),
121 init_utsname()->version
);
122 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
123 " disables this message.\n");
125 hung_task_show_lock
= true;
128 touch_nmi_watchdog();
130 if (sysctl_hung_task_panic
) {
131 hung_task_show_lock
= true;
132 hung_task_call_panic
= true;
137 * To avoid extending the RCU grace period for an unbounded amount of time,
138 * periodically exit the critical section and enter a new one.
140 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
141 * to exit the grace period. For classic RCU, a reschedule is required.
143 static bool rcu_lock_break(struct task_struct
*g
, struct task_struct
*t
)
152 can_cont
= pid_alive(g
) && pid_alive(t
);
160 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
161 * a really long time (120 seconds). If that happens, print out
164 static void check_hung_uninterruptible_tasks(unsigned long timeout
)
166 int max_count
= sysctl_hung_task_check_count
;
167 int batch_count
= HUNG_TASK_BATCHING
;
168 struct task_struct
*g
, *t
;
171 * If the system crashed already then all bets are off,
172 * do not report extra hung tasks:
174 if (test_taint(TAINT_DIE
) || did_panic
)
177 hung_task_show_lock
= false;
179 for_each_process_thread(g
, t
) {
182 if (!--batch_count
) {
183 batch_count
= HUNG_TASK_BATCHING
;
184 if (!rcu_lock_break(g
, t
))
187 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
188 if (t
->state
== TASK_UNINTERRUPTIBLE
)
189 check_hung_task(t
, timeout
);
193 if (hung_task_show_lock
)
194 debug_show_all_locks();
195 if (hung_task_call_panic
) {
196 trigger_all_cpu_backtrace();
197 panic("hung_task: blocked tasks");
201 static long hung_timeout_jiffies(unsigned long last_checked
,
202 unsigned long timeout
)
204 /* timeout of 0 will disable the watchdog */
205 return timeout
? last_checked
- jiffies
+ timeout
* HZ
:
206 MAX_SCHEDULE_TIMEOUT
;
210 * Process updating of timeout sysctl
212 int proc_dohung_task_timeout_secs(struct ctl_table
*table
, int write
,
214 size_t *lenp
, loff_t
*ppos
)
218 ret
= proc_doulongvec_minmax(table
, write
, buffer
, lenp
, ppos
);
223 wake_up_process(watchdog_task
);
229 static atomic_t reset_hung_task
= ATOMIC_INIT(0);
231 void reset_hung_task_detector(void)
233 atomic_set(&reset_hung_task
, 1);
235 EXPORT_SYMBOL_GPL(reset_hung_task_detector
);
238 * kthread which checks for tasks stuck in D state
240 static int watchdog(void *dummy
)
242 unsigned long hung_last_checked
= jiffies
;
244 set_user_nice(current
, 0);
247 unsigned long timeout
= sysctl_hung_task_timeout_secs
;
248 long t
= hung_timeout_jiffies(hung_last_checked
, timeout
);
251 if (!atomic_xchg(&reset_hung_task
, 0))
252 check_hung_uninterruptible_tasks(timeout
);
253 hung_last_checked
= jiffies
;
256 schedule_timeout_interruptible(t
);
262 static int __init
hung_task_init(void)
264 atomic_notifier_chain_register(&panic_notifier_list
, &panic_block
);
265 watchdog_task
= kthread_run(watchdog
, NULL
, "khungtaskd");
269 subsys_initcall(hung_task_init
);