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>
21 * The number of tasks checked:
23 unsigned long __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
26 * Limit number of tasks checked in a batch.
28 * This value controls the preemptibility of khungtaskd since preemption
29 * is disabled during the critical section. It also controls the size of
30 * the RCU grace period. So it needs to be upper-bound.
32 #define HUNG_TASK_BATCHING 1024
35 * Zero means infinite timeout - no checking done:
37 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
39 unsigned long __read_mostly sysctl_hung_task_warnings = 10;
41 static int __read_mostly did_panic;
43 static struct task_struct *watchdog_task;
46 * Should we panic (and reboot, if panic_timeout= is set) when a
47 * hung task is detected:
49 unsigned int __read_mostly sysctl_hung_task_panic =
50 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
52 static int __init hung_task_panic_setup(char *str)
54 sysctl_hung_task_panic = simple_strtoul(str, NULL, 0);
58 __setup("hung_task_panic=", hung_task_panic_setup);
61 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
68 static struct notifier_block panic_block = {
69 .notifier_call = hung_task_panic,
72 static void check_hung_task(struct task_struct *t, unsigned long timeout)
74 unsigned long switch_count = t->nvcsw + t->nivcsw;
77 * Ensure the task is not frozen.
78 * Also, skip vfork and any other user process that freezer should skip.
80 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
84 * When a freshly created task is scheduled once, changes its state to
85 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
88 if (unlikely(!switch_count))
91 if (switch_count != t->last_switch_count) {
92 t->last_switch_count = switch_count;
95 if (!sysctl_hung_task_warnings)
97 sysctl_hung_task_warnings--;
100 * Ok, the task did not get scheduled for more than 2 minutes,
103 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
104 t->comm, t->pid, timeout);
105 pr_err(" %s %s %.*s\n",
106 print_tainted(), init_utsname()->release,
107 (int)strcspn(init_utsname()->version, " "),
108 init_utsname()->version);
109 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
110 " disables this message.\n");
112 debug_show_held_locks(t);
114 touch_nmi_watchdog();
116 if (sysctl_hung_task_panic) {
117 trigger_all_cpu_backtrace();
118 panic("hung_task: blocked tasks");
123 * To avoid extending the RCU grace period for an unbounded amount of time,
124 * periodically exit the critical section and enter a new one.
126 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
127 * to exit the grace period. For classic RCU, a reschedule is required.
129 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
138 can_cont = pid_alive(g) && pid_alive(t);
146 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
147 * a really long time (120 seconds). If that happens, print out
150 static void check_hung_uninterruptible_tasks(unsigned long timeout)
152 int max_count = sysctl_hung_task_check_count;
153 int batch_count = HUNG_TASK_BATCHING;
154 struct task_struct *g, *t;
157 * If the system crashed already then all bets are off,
158 * do not report extra hung tasks:
160 if (test_taint(TAINT_DIE) || did_panic)
164 do_each_thread(g, t) {
167 if (!--batch_count) {
168 batch_count = HUNG_TASK_BATCHING;
169 if (!rcu_lock_break(g, t))
172 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
173 if (t->state == TASK_UNINTERRUPTIBLE)
174 check_hung_task(t, timeout);
175 } while_each_thread(g, t);
180 static unsigned long timeout_jiffies(unsigned long timeout)
182 /* timeout of 0 will disable the watchdog */
183 return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
187 * Process updating of timeout sysctl
189 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
191 size_t *lenp, loff_t *ppos)
195 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
200 wake_up_process(watchdog_task);
207 * kthread which checks for tasks stuck in D state
209 static int watchdog(void *dummy)
211 set_user_nice(current, 0);
214 unsigned long timeout = sysctl_hung_task_timeout_secs;
216 while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
217 timeout = sysctl_hung_task_timeout_secs;
219 check_hung_uninterruptible_tasks(timeout);
225 static int __init hung_task_init(void)
227 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
228 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
233 module_init(hung_task_init);