softlockup: decouple hung tasks check from softlockup detection
Decoupling allows: * hung tasks check to happen at very low priority * hung tasks check and softlockup to be enabled/disabled independently at compile and/or run-time * individual panic settings to be enabled disabled independently at compile and/or run-time * softlockup threshold to be reduced without increasing hung tasks poll frequency (hung task check is expensive relative to softlock watchdog) * hung task check to be zero over-head when disabled at run-time Signed-off-by: Mandeep Singh Baines <msb@google.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Mandeep Singh Baines
Ingo Molnar
parent
c903ff8379
commit
e162b39a36
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@ -297,9 +297,6 @@ extern int proc_dosoftlockup_thresh(struct ctl_table *table, int write,
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struct file *filp, void __user *buffer,
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size_t *lenp, loff_t *ppos);
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extern unsigned int softlockup_panic;
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extern unsigned long sysctl_hung_task_check_count;
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extern unsigned long sysctl_hung_task_timeout_secs;
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extern unsigned long sysctl_hung_task_warnings;
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extern int softlockup_thresh;
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#else
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static inline void softlockup_tick(void)
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@ -316,6 +313,15 @@ static inline void touch_all_softlockup_watchdogs(void)
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}
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#endif
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#ifdef CONFIG_DETECT_HUNG_TASK
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extern unsigned int sysctl_hung_task_panic;
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extern unsigned long sysctl_hung_task_check_count;
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extern unsigned long sysctl_hung_task_timeout_secs;
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extern unsigned long sysctl_hung_task_warnings;
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extern int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
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struct file *filp, void __user *buffer,
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size_t *lenp, loff_t *ppos);
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#endif
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/* Attach to any functions which should be ignored in wchan output. */
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#define __sched __attribute__((__section__(".sched.text")))
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@ -1236,7 +1242,7 @@ struct task_struct {
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/* ipc stuff */
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struct sysv_sem sysvsem;
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#endif
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#ifdef CONFIG_DETECT_SOFTLOCKUP
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#ifdef CONFIG_DETECT_HUNG_TASK
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/* hung task detection */
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unsigned long last_switch_timestamp;
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unsigned long last_switch_count;
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@ -74,6 +74,7 @@ obj-$(CONFIG_AUDIT_TREE) += audit_tree.o
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obj-$(CONFIG_KPROBES) += kprobes.o
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obj-$(CONFIG_KGDB) += kgdb.o
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obj-$(CONFIG_DETECT_SOFTLOCKUP) += softlockup.o
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obj-$(CONFIG_DETECT_HUNG_TASK) += hung_task.o
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obj-$(CONFIG_GENERIC_HARDIRQS) += irq/
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obj-$(CONFIG_SECCOMP) += seccomp.o
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obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
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@ -0,0 +1,198 @@
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/*
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* Detect Hung Task
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*
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* kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
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*
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*/
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#include <linux/mm.h>
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#include <linux/cpu.h>
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#include <linux/nmi.h>
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#include <linux/init.h>
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#include <linux/delay.h>
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#include <linux/freezer.h>
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#include <linux/kthread.h>
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#include <linux/lockdep.h>
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#include <linux/module.h>
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#include <linux/sysctl.h>
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/*
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* Have a reasonable limit on the number of tasks checked:
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*/
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unsigned long __read_mostly sysctl_hung_task_check_count = 1024;
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/*
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* Zero means infinite timeout - no checking done:
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*/
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unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;
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static unsigned long __read_mostly hung_task_poll_jiffies;
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unsigned long __read_mostly sysctl_hung_task_warnings = 10;
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static int __read_mostly did_panic;
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static struct task_struct *watchdog_task;
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/*
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* Should we panic (and reboot, if panic_timeout= is set) when a
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* hung task is detected:
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*/
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unsigned int __read_mostly sysctl_hung_task_panic =
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CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
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static int __init hung_task_panic_setup(char *str)
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{
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sysctl_hung_task_panic = simple_strtoul(str, NULL, 0);
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return 1;
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}
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__setup("hung_task_panic=", hung_task_panic_setup);
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static int
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hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
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{
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did_panic = 1;
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return NOTIFY_DONE;
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}
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static struct notifier_block panic_block = {
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.notifier_call = hung_task_panic,
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};
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/*
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* Returns seconds, approximately. We don't need nanosecond
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* resolution, and we don't need to waste time with a big divide when
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* 2^30ns == 1.074s.
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*/
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static unsigned long get_timestamp(void)
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{
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int this_cpu = raw_smp_processor_id();
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return cpu_clock(this_cpu) >> 30LL; /* 2^30 ~= 10^9 */
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}
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static void check_hung_task(struct task_struct *t, unsigned long now)
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{
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unsigned long switch_count = t->nvcsw + t->nivcsw;
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if (t->flags & PF_FROZEN)
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return;
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if (switch_count != t->last_switch_count || !t->last_switch_timestamp) {
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t->last_switch_count = switch_count;
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t->last_switch_timestamp = now;
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return;
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}
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if ((long)(now - t->last_switch_timestamp) <
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sysctl_hung_task_timeout_secs)
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return;
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if (!sysctl_hung_task_warnings)
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return;
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sysctl_hung_task_warnings--;
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/*
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* Ok, the task did not get scheduled for more than 2 minutes,
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* complain:
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*/
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printk(KERN_ERR "INFO: task %s:%d blocked for more than "
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"%ld seconds.\n", t->comm, t->pid,
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sysctl_hung_task_timeout_secs);
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printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
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" disables this message.\n");
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sched_show_task(t);
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__debug_show_held_locks(t);
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t->last_switch_timestamp = now;
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touch_nmi_watchdog();
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if (sysctl_hung_task_panic)
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panic("hung_task: blocked tasks");
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}
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/*
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* Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
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* a really long time (120 seconds). If that happens, print out
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* a warning.
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*/
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static void check_hung_uninterruptible_tasks(void)
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{
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int max_count = sysctl_hung_task_check_count;
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unsigned long now = get_timestamp();
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struct task_struct *g, *t;
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/*
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* If the system crashed already then all bets are off,
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* do not report extra hung tasks:
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*/
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if (test_taint(TAINT_DIE) || did_panic)
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return;
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read_lock(&tasklist_lock);
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do_each_thread(g, t) {
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if (!--max_count)
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goto unlock;
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/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
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if (t->state == TASK_UNINTERRUPTIBLE)
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check_hung_task(t, now);
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} while_each_thread(g, t);
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unlock:
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read_unlock(&tasklist_lock);
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}
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static void update_poll_jiffies(void)
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{
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/* timeout of 0 will disable the watchdog */
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if (sysctl_hung_task_timeout_secs == 0)
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hung_task_poll_jiffies = MAX_SCHEDULE_TIMEOUT;
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else
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hung_task_poll_jiffies = sysctl_hung_task_timeout_secs * HZ / 2;
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}
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/*
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* Process updating of timeout sysctl
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*/
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int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
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struct file *filp, void __user *buffer,
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size_t *lenp, loff_t *ppos)
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{
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int ret;
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ret = proc_doulongvec_minmax(table, write, filp, buffer, lenp, ppos);
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if (ret || !write)
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goto out;
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update_poll_jiffies();
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wake_up_process(watchdog_task);
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out:
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return ret;
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}
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/*
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* kthread which checks for tasks stuck in D state
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*/
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static int watchdog(void *dummy)
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{
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set_user_nice(current, 0);
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update_poll_jiffies();
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for ( ; ; ) {
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while (schedule_timeout_interruptible(hung_task_poll_jiffies));
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check_hung_uninterruptible_tasks();
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}
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return 0;
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}
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static int __init hung_task_init(void)
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{
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atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
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watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
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return 0;
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}
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module_init(hung_task_init);
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@ -165,98 +165,12 @@ void softlockup_tick(void)
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panic("softlockup: hung tasks");
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}
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/*
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* Have a reasonable limit on the number of tasks checked:
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*/
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unsigned long __read_mostly sysctl_hung_task_check_count = 1024;
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/*
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* Zero means infinite timeout - no checking done:
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*/
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unsigned long __read_mostly sysctl_hung_task_timeout_secs = 480;
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unsigned long __read_mostly sysctl_hung_task_warnings = 10;
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/*
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* Only do the hung-tasks check on one CPU:
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*/
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static int check_cpu __read_mostly = -1;
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static void check_hung_task(struct task_struct *t, unsigned long now)
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{
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unsigned long switch_count = t->nvcsw + t->nivcsw;
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if (t->flags & PF_FROZEN)
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return;
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if (switch_count != t->last_switch_count || !t->last_switch_timestamp) {
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t->last_switch_count = switch_count;
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t->last_switch_timestamp = now;
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return;
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}
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if ((long)(now - t->last_switch_timestamp) <
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sysctl_hung_task_timeout_secs)
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return;
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if (!sysctl_hung_task_warnings)
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return;
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sysctl_hung_task_warnings--;
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/*
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* Ok, the task did not get scheduled for more than 2 minutes,
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* complain:
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*/
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printk(KERN_ERR "INFO: task %s:%d blocked for more than "
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"%ld seconds.\n", t->comm, t->pid,
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sysctl_hung_task_timeout_secs);
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printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
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" disables this message.\n");
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sched_show_task(t);
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__debug_show_held_locks(t);
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t->last_switch_timestamp = now;
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touch_nmi_watchdog();
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if (softlockup_panic)
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panic("softlockup: blocked tasks");
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}
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/*
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* Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
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* a really long time (120 seconds). If that happens, print out
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* a warning.
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*/
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static void check_hung_uninterruptible_tasks(int this_cpu)
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{
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int max_count = sysctl_hung_task_check_count;
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unsigned long now = get_timestamp(this_cpu);
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struct task_struct *g, *t;
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/*
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* If the system crashed already then all bets are off,
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* do not report extra hung tasks:
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*/
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if (test_taint(TAINT_DIE) || did_panic)
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return;
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read_lock(&tasklist_lock);
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do_each_thread(g, t) {
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if (!--max_count)
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goto unlock;
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/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
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if (t->state == TASK_UNINTERRUPTIBLE)
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check_hung_task(t, now);
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} while_each_thread(g, t);
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unlock:
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read_unlock(&tasklist_lock);
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}
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/*
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* The watchdog thread - runs every second and touches the timestamp.
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*/
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static int watchdog(void *__bind_cpu)
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{
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struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
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int this_cpu = (long)__bind_cpu;
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sched_setscheduler(current, SCHED_FIFO, ¶m);
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@ -276,11 +190,6 @@ static int watchdog(void *__bind_cpu)
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if (kthread_should_stop())
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break;
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if (this_cpu == check_cpu) {
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if (sysctl_hung_task_timeout_secs)
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check_hung_uninterruptible_tasks(this_cpu);
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}
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set_current_state(TASK_INTERRUPTIBLE);
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}
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__set_current_state(TASK_RUNNING);
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@ -312,18 +221,9 @@ cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
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break;
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case CPU_ONLINE:
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case CPU_ONLINE_FROZEN:
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check_cpu = cpumask_any(cpu_online_mask);
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wake_up_process(per_cpu(watchdog_task, hotcpu));
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break;
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#ifdef CONFIG_HOTPLUG_CPU
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case CPU_DOWN_PREPARE:
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case CPU_DOWN_PREPARE_FROZEN:
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if (hotcpu == check_cpu) {
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/* Pick any other online cpu. */
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check_cpu = cpumask_any_but(cpu_online_mask, hotcpu);
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}
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break;
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case CPU_UP_CANCELED:
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case CPU_UP_CANCELED_FROZEN:
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if (!per_cpu(watchdog_task, hotcpu))
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@ -805,6 +805,19 @@ static struct ctl_table kern_table[] = {
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.extra1 = &neg_one,
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.extra2 = &sixty,
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},
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#endif
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#ifdef CONFIG_DETECT_HUNG_TASK
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{
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.ctl_name = CTL_UNNUMBERED,
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.procname = "hung_task_panic",
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.data = &sysctl_hung_task_panic,
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.maxlen = sizeof(int),
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.mode = 0644,
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.proc_handler = &proc_dointvec_minmax,
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.strategy = &sysctl_intvec,
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.extra1 = &zero,
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.extra2 = &one,
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},
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{
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.ctl_name = CTL_UNNUMBERED,
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.procname = "hung_task_check_count",
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@ -820,7 +833,7 @@ static struct ctl_table kern_table[] = {
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.data = &sysctl_hung_task_timeout_secs,
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.maxlen = sizeof(unsigned long),
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.mode = 0644,
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.proc_handler = &proc_doulongvec_minmax,
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.proc_handler = &proc_dohung_task_timeout_secs,
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.strategy = &sysctl_intvec,
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},
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{
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@ -186,6 +186,44 @@ config BOOTPARAM_SOFTLOCKUP_PANIC_VALUE
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default 0 if !BOOTPARAM_SOFTLOCKUP_PANIC
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default 1 if BOOTPARAM_SOFTLOCKUP_PANIC
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config DETECT_HUNG_TASK
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bool "Detect Hung Tasks"
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depends on DEBUG_KERNEL
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default y
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help
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Say Y here to enable the kernel to detect "hung tasks",
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which are bugs that cause the task to be stuck in
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uninterruptible "D" state indefinitiley.
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When a hung task is detected, the kernel will print the
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current stack trace (which you should report), but the
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task will stay in uninterruptible state. If lockdep is
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enabled then all held locks will also be reported. This
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feature has negligible overhead.
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config BOOTPARAM_HUNG_TASK_PANIC
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bool "Panic (Reboot) On Hung Tasks"
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depends on DETECT_HUNG_TASK
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help
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Say Y here to enable the kernel to panic on "hung tasks",
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which are bugs that cause the kernel to leave a task stuck
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in uninterruptible "D" state.
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The panic can be used in combination with panic_timeout,
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to cause the system to reboot automatically after a
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hung task has been detected. This feature is useful for
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high-availability systems that have uptime guarantees and
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where a hung tasks must be resolved ASAP.
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Say N if unsure.
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config BOOTPARAM_HUNG_TASK_PANIC_VALUE
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int
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depends on DETECT_HUNG_TASK
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range 0 1
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default 0 if !BOOTPARAM_HUNG_TASK_PANIC
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default 1 if BOOTPARAM_HUNG_TASK_PANIC
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config SCHED_DEBUG
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bool "Collect scheduler debugging info"
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depends on DEBUG_KERNEL && PROC_FS
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