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/module.h>
17 #include <linux/sysctl.h>
20 * Have a reasonable limit on the number of tasks checked:
22 unsigned long __read_mostly sysctl_hung_task_check_count
= 1024;
25 * Zero means infinite timeout - no checking done:
27 unsigned long __read_mostly sysctl_hung_task_timeout_secs
= 120;
28 static unsigned long __read_mostly hung_task_poll_jiffies
;
30 unsigned long __read_mostly sysctl_hung_task_warnings
= 10;
32 static int __read_mostly did_panic
;
34 static struct task_struct
*watchdog_task
;
37 * Should we panic (and reboot, if panic_timeout= is set) when a
38 * hung task is detected:
40 unsigned int __read_mostly sysctl_hung_task_panic
=
41 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE
;
43 static int __init
hung_task_panic_setup(char *str
)
45 sysctl_hung_task_panic
= simple_strtoul(str
, NULL
, 0);
49 __setup("hung_task_panic=", hung_task_panic_setup
);
52 hung_task_panic(struct notifier_block
*this, unsigned long event
, void *ptr
)
59 static struct notifier_block panic_block
= {
60 .notifier_call
= hung_task_panic
,
64 * Returns seconds, approximately. We don't need nanosecond
65 * resolution, and we don't need to waste time with a big divide when
68 static unsigned long get_timestamp(void)
70 int this_cpu
= raw_smp_processor_id();
72 return cpu_clock(this_cpu
) >> 30LL; /* 2^30 ~= 10^9 */
75 static void check_hung_task(struct task_struct
*t
, unsigned long now
,
76 unsigned long timeout
)
78 unsigned long switch_count
= t
->nvcsw
+ t
->nivcsw
;
80 if (t
->flags
& PF_FROZEN
)
83 if (switch_count
!= t
->last_switch_count
|| !t
->last_switch_timestamp
) {
84 t
->last_switch_count
= switch_count
;
85 t
->last_switch_timestamp
= now
;
88 if ((long)(now
- t
->last_switch_timestamp
) < timeout
)
90 if (!sysctl_hung_task_warnings
)
92 sysctl_hung_task_warnings
--;
95 * Ok, the task did not get scheduled for more than 2 minutes,
98 printk(KERN_ERR
"INFO: task %s:%d blocked for more than "
99 "%ld seconds.\n", t
->comm
, t
->pid
, timeout
);
100 printk(KERN_ERR
"\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
101 " disables this message.\n");
103 __debug_show_held_locks(t
);
105 t
->last_switch_timestamp
= now
;
106 touch_nmi_watchdog();
108 if (sysctl_hung_task_panic
)
109 panic("hung_task: blocked tasks");
113 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
114 * a really long time (120 seconds). If that happens, print out
117 static void check_hung_uninterruptible_tasks(unsigned long timeout
)
119 int max_count
= sysctl_hung_task_check_count
;
120 unsigned long now
= get_timestamp();
121 struct task_struct
*g
, *t
;
124 * If the system crashed already then all bets are off,
125 * do not report extra hung tasks:
127 if (test_taint(TAINT_DIE
) || did_panic
)
130 read_lock(&tasklist_lock
);
131 do_each_thread(g
, t
) {
134 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
135 if (t
->state
== TASK_UNINTERRUPTIBLE
)
136 check_hung_task(t
, now
, timeout
);
137 } while_each_thread(g
, t
);
139 read_unlock(&tasklist_lock
);
142 static void update_poll_jiffies(void)
144 /* timeout of 0 will disable the watchdog */
145 if (sysctl_hung_task_timeout_secs
== 0)
146 hung_task_poll_jiffies
= MAX_SCHEDULE_TIMEOUT
;
148 hung_task_poll_jiffies
= sysctl_hung_task_timeout_secs
* HZ
/ 2;
152 * Process updating of timeout sysctl
154 int proc_dohung_task_timeout_secs(struct ctl_table
*table
, int write
,
155 struct file
*filp
, void __user
*buffer
,
156 size_t *lenp
, loff_t
*ppos
)
160 ret
= proc_doulongvec_minmax(table
, write
, filp
, buffer
, lenp
, ppos
);
165 update_poll_jiffies();
167 wake_up_process(watchdog_task
);
174 * kthread which checks for tasks stuck in D state
176 static int watchdog(void *dummy
)
178 set_user_nice(current
, 0);
179 update_poll_jiffies();
182 unsigned long timeout
;
184 while (schedule_timeout_interruptible(hung_task_poll_jiffies
));
187 * Need to cache timeout here to avoid timeout being set
188 * to 0 via sysctl while inside check_hung_*_tasks().
190 timeout
= sysctl_hung_task_timeout_secs
;
192 check_hung_uninterruptible_tasks(timeout
);
198 static int __init
hung_task_init(void)
200 atomic_notifier_chain_register(&panic_notifier_list
, &panic_block
);
201 watchdog_task
= kthread_run(watchdog
, NULL
, "khungtaskd");
206 module_init(hung_task_init
);