[PATCH v2] kernel/hung_task.c: allow to set checking interval separately from timeout
From: Dmitry Vyukov
Date: Mon Jun 11 2018 - 07:10:16 EST
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.
Signed-off-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: syzkaller@xxxxxxxxxxxxxxxx
---
Changes since v1:
- add entry to Documentation/sysctl/kernel.txt
- rename hung_task_period_secs sysctl to hung_task_check_interval_secs
---
Documentation/sysctl/kernel.txt | 15 ++++++++++++++-
include/linux/sched.h | 1 +
include/linux/sched/sysctl.h | 1 +
kernel/fork.c | 1 +
kernel/hung_task.c | 15 ++++++++++++++-
kernel/sysctl.c | 8 ++++++++
6 files changed, 39 insertions(+), 2 deletions(-)
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index eded671d55eb..71f1b8716ba9 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -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
- kexec_load_disabled
- kptr_restrict
@@ -354,7 +355,7 @@ 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.
@@ -363,6 +364,18 @@ 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
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 3aa4fcb74e76..0db55fbe47a4 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -849,6 +849,7 @@ 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;
diff --git a/include/linux/sched/sysctl.h b/include/linux/sched/sysctl.h
index 1c1a1512ec55..8ada9a538bc1 100644
--- a/include/linux/sched/sysctl.h
+++ b/include/linux/sched/sysctl.h
@@ -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,
diff --git a/kernel/fork.c b/kernel/fork.c
index 08c6e5e217a0..3c095595b940 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1262,6 +1262,7 @@ 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;
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 32b479468e4d..b9132d1269ef 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -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);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 6a78cf70761d..ef873976a227 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1098,6 +1098,14 @@ static struct ctl_table kern_table[] = {
.proc_handler = proc_dohung_task_timeout_secs,
.extra2 = &hung_task_timeout_max,
},
+ {
+ .procname = "hung_task_check_interval_secs",
+ .data = &sysctl_hung_task_check_interval_secs,
+ .maxlen = sizeof(unsigned long),
+ .mode = 0644,
+ .proc_handler = proc_dohung_task_timeout_secs,
+ .extra2 = &hung_task_timeout_max,
+ },
{
.procname = "hung_task_warnings",
.data = &sysctl_hung_task_warnings,
--
2.18.0.rc1.242.g61856ae69a-goog