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a2e5144538
Currently task hung checking interval is equal to timeout, as the result hung is detected anywhere between timeout and 2*timeout. This is fine for most interactive environments, but this hurts automated testing setups (syzbot). In an automated setup we need to strictly order CPU lockup < RCU stall < workqueue lockup < task hung < silent loss, so that RCU stall is not detected as task hung and task hung is not detected as silent machine loss. The large variance in task hung detection timeout requires setting silent machine loss timeout to a very large value (e.g. if task hung is 3 mins, then silent loss need to be set to ~7 mins). The additional 3 minutes significantly reduce testing efficiency because usually we crash kernel within a minute, and this can add hours to bug localization process as it needs to do dozens of tests. Allow setting checking interval separately from timeout. This allows to set timeout to, say, 3 minutes, but checking interval to 10 secs. The interval is controlled via a new hung_task_check_interval_secs sysctl, similar to the existing hung_task_timeout_secs sysctl. The default value of 0 results in the current behavior: checking interval is equal to timeout. [akpm@linux-foundation.org: update hung_task_timeout_max's comment] Link: http://lkml.kernel.org/r/20180611111004.203513-1-dvyukov@google.com Signed-off-by: Dmitry Vyukov <dvyukov@google.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
283 lines
6.6 KiB
C
283 lines
6.6 KiB
C
/*
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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/export.h>
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#include <linux/sysctl.h>
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#include <linux/utsname.h>
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#include <linux/sched/signal.h>
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#include <linux/sched/debug.h>
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#include <trace/events/sched.h>
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/*
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* The number of tasks checked:
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*/
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int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
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/*
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* Limit number of tasks checked in a batch.
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*
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* This value controls the preemptibility of khungtaskd since preemption
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* is disabled during the critical section. It also controls the size of
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* the RCU grace period. So it needs to be upper-bound.
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*/
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#define HUNG_TASK_BATCHING 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 = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
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/*
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* Zero (default value) means use sysctl_hung_task_timeout_secs:
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*/
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unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
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int __read_mostly sysctl_hung_task_warnings = 10;
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static int __read_mostly did_panic;
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static bool hung_task_show_lock;
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static bool hung_task_call_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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int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
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if (rc)
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return rc;
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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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static void check_hung_task(struct task_struct *t, unsigned long timeout)
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{
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unsigned long switch_count = t->nvcsw + t->nivcsw;
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/*
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* Ensure the task is not frozen.
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* Also, skip vfork and any other user process that freezer should skip.
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*/
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if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
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return;
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/*
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* When a freshly created task is scheduled once, changes its state to
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* TASK_UNINTERRUPTIBLE without having ever been switched out once, it
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* musn't be checked.
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*/
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if (unlikely(!switch_count))
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return;
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if (switch_count != t->last_switch_count) {
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t->last_switch_count = switch_count;
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t->last_switch_time = jiffies;
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return;
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}
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if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
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return;
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trace_sched_process_hang(t);
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if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic)
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return;
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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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if (sysctl_hung_task_warnings) {
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if (sysctl_hung_task_warnings > 0)
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sysctl_hung_task_warnings--;
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pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
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t->comm, t->pid, timeout);
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pr_err(" %s %s %.*s\n",
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print_tainted(), init_utsname()->release,
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(int)strcspn(init_utsname()->version, " "),
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init_utsname()->version);
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pr_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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hung_task_show_lock = true;
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}
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touch_nmi_watchdog();
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if (sysctl_hung_task_panic) {
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hung_task_show_lock = true;
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hung_task_call_panic = true;
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}
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}
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/*
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* To avoid extending the RCU grace period for an unbounded amount of time,
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* periodically exit the critical section and enter a new one.
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*
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* For preemptible RCU it is sufficient to call rcu_read_unlock in order
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* to exit the grace period. For classic RCU, a reschedule is required.
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*/
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static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
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{
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bool can_cont;
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get_task_struct(g);
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get_task_struct(t);
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rcu_read_unlock();
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cond_resched();
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rcu_read_lock();
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can_cont = pid_alive(g) && pid_alive(t);
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put_task_struct(t);
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put_task_struct(g);
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return can_cont;
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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(unsigned long timeout)
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{
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int max_count = sysctl_hung_task_check_count;
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int batch_count = HUNG_TASK_BATCHING;
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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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hung_task_show_lock = false;
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rcu_read_lock();
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for_each_process_thread(g, t) {
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if (!max_count--)
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goto unlock;
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if (!--batch_count) {
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batch_count = HUNG_TASK_BATCHING;
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if (!rcu_lock_break(g, t))
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goto unlock;
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}
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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, timeout);
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}
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unlock:
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rcu_read_unlock();
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if (hung_task_show_lock)
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debug_show_all_locks();
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if (hung_task_call_panic) {
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trigger_all_cpu_backtrace();
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panic("hung_task: blocked tasks");
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}
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}
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static long hung_timeout_jiffies(unsigned long last_checked,
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unsigned long timeout)
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{
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/* timeout of 0 will disable the watchdog */
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return timeout ? last_checked - jiffies + timeout * HZ :
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MAX_SCHEDULE_TIMEOUT;
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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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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, buffer, lenp, ppos);
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if (ret || !write)
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goto out;
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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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static atomic_t reset_hung_task = ATOMIC_INIT(0);
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void reset_hung_task_detector(void)
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{
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atomic_set(&reset_hung_task, 1);
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}
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EXPORT_SYMBOL_GPL(reset_hung_task_detector);
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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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unsigned long hung_last_checked = jiffies;
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set_user_nice(current, 0);
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for ( ; ; ) {
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unsigned long timeout = sysctl_hung_task_timeout_secs;
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unsigned long interval = sysctl_hung_task_check_interval_secs;
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long t;
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if (interval == 0)
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interval = timeout;
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interval = min_t(unsigned long, interval, timeout);
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t = hung_timeout_jiffies(hung_last_checked, interval);
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if (t <= 0) {
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if (!atomic_xchg(&reset_hung_task, 0))
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check_hung_uninterruptible_tasks(timeout);
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hung_last_checked = jiffies;
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continue;
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}
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schedule_timeout_interruptible(t);
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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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subsys_initcall(hung_task_init);
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