Commit a2e51445 authored by Dmitry Vyukov's avatar Dmitry Vyukov Committed by Linus Torvalds
Browse files

kernel/hung_task.c: allow to set checking interval separately from timeout 

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: default avatarDmitry 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 91bc9aaf

Documentation/sysctl/kernel.txt

+14 −1
Original line number Diff line number Diff line
@@ -38,6 +38,7 @@ show up in /proc/sys/kernel: 
- hung_task_panic

- hung_task_check_count

- hung_task_timeout_secs

- hung_task_check_interval_secs

- hung_task_warnings

- hyperv_record_panic_msg

- kexec_load_disabled
@@ -355,7 +356,7 @@ This file shows up if CONFIG_DETECT_HUNG_TASK is enabled. 


hung_task_timeout_secs:



Check interval. When a task in D state did not get scheduled

When a task in D state did not get scheduled

for more than this value report a warning.

This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
@@ -364,6 +365,18 @@ Possible values to set are in range {0..LONG_MAX/HZ}. 


==============================================================



hung_task_check_interval_secs:



Hung task check interval. If hung task checking is enabled

(see hung_task_timeout_secs), the check is done every

hung_task_check_interval_secs seconds.

This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.



0 (default): means use hung_task_timeout_secs as checking interval.

Possible values to set are in range {0..LONG_MAX/HZ}.



==============================================================



hung_task_warnings:



The maximum number of warnings to report. During a check interval

include/linux/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -853,6 +853,7 @@ struct task_struct { 
#endif

#ifdef CONFIG_DETECT_HUNG_TASK

	unsigned long			last_switch_count;

	unsigned long			last_switch_time;

#endif

	/* Filesystem information: */

	struct fs_struct		*fs;

include/linux/sched/sysctl.h

+1 −0
Original line number Diff line number Diff line
@@ -10,6 +10,7 @@ struct ctl_table; 
extern int	     sysctl_hung_task_check_count;

extern unsigned int  sysctl_hung_task_panic;

extern unsigned long sysctl_hung_task_timeout_secs;

extern unsigned long sysctl_hung_task_check_interval_secs;

extern int sysctl_hung_task_warnings;

extern int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,

					 void __user *buffer,

kernel/fork.c

+1 −0
Original line number Diff line number Diff line
@@ -1302,6 +1302,7 @@ static int copy_mm(unsigned long clone_flags, struct task_struct *tsk) 
	tsk->nvcsw = tsk->nivcsw = 0;

#ifdef CONFIG_DETECT_HUNG_TASK

	tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;

	tsk->last_switch_time = 0;

#endif



	tsk->mm = NULL;

kernel/hung_task.c

+14 −1
Original line number Diff line number Diff line
@@ -40,6 +40,11 @@ int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT; 
 */

unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;



/*

 * Zero (default value) means use sysctl_hung_task_timeout_secs:

 */

unsigned long __read_mostly sysctl_hung_task_check_interval_secs;



int __read_mostly sysctl_hung_task_warnings = 10;



static int __read_mostly did_panic;
@@ -98,8 +103,11 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout) 


	if (switch_count != t->last_switch_count) {

		t->last_switch_count = switch_count;

		t->last_switch_time = jiffies;

		return;

	}

	if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))

		return;



	trace_sched_process_hang(t);
@@ -245,8 +253,13 @@ static int watchdog(void *dummy) 


	for ( ; ; ) {

		unsigned long timeout = sysctl_hung_task_timeout_secs;

		long t = hung_timeout_jiffies(hung_last_checked, timeout);

		unsigned long interval = sysctl_hung_task_check_interval_secs;

		long t;



		if (interval == 0)

			interval = timeout;

		interval = min_t(unsigned long, interval, timeout);

		t = hung_timeout_jiffies(hung_last_checked, interval);

		if (t <= 0) {

			if (!atomic_xchg(&reset_hung_task, 0))

				check_hung_uninterruptible_tasks(timeout);

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