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Subject[PATCH v3] kernel/hung_task.c: disable on suspend
Date
It is possible to observe hung_task complaints when system goes to
suspend-to-idle state:

# echo freeze > /sys/power/state

PM: Syncing filesystems ... done.
Freezing user space processes ... (elapsed 0.001 seconds) done.
OOM killer disabled.
Freezing remaining freezable tasks ... (elapsed 0.002 seconds) done.
sd 0:0:0:0: [sda] Synchronizing SCSI cache
INFO: task bash:1569 blocked for more than 120 seconds.
Not tainted 4.19.0-rc3_+ #687
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
bash D 0 1569 604 0x00000000
Call Trace:
? __schedule+0x1fe/0x7e0
schedule+0x28/0x80
suspend_devices_and_enter+0x4ac/0x750
pm_suspend+0x2c0/0x310

Register a PM notifier to disable the detector on suspend and re-enable
back on wakeup.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
Changes since v2:
- Resurrect 'v1' as zeroing timeouts can be racy [Rafael J. Wysocki]
---
kernel/hung_task.c | 28 +++++++++++++++++++++++++++-
1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index b9132d1269ef..41955c5d8427 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -15,6 +15,7 @@
#include <linux/lockdep.h>
#include <linux/export.h>
#include <linux/sysctl.h>
+#include <linux/suspend.h>
#include <linux/utsname.h>
#include <linux/sched/signal.h>
#include <linux/sched/debug.h>
@@ -242,6 +243,26 @@ void reset_hung_task_detector(void)
}
EXPORT_SYMBOL_GPL(reset_hung_task_detector);

+static bool hung_detector_suspended;
+
+static int hungtask_pm_notify(struct notifier_block *self,
+ unsigned long action, void *hcpu)
+{
+ switch (action) {
+ case PM_SUSPEND_PREPARE:
+ case PM_HIBERNATION_PREPARE:
+ hung_detector_suspended = true;
+ break;
+ case PM_POST_SUSPEND:
+ case PM_POST_HIBERNATION:
+ hung_detector_suspended = false;
+ break;
+ default:
+ break;
+ }
+ return NOTIFY_OK;
+}
+
/*
* kthread which checks for tasks stuck in D state
*/
@@ -261,7 +282,8 @@ static int watchdog(void *dummy)
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))
+ if (!atomic_xchg(&reset_hung_task, 0) &&
+ !hung_detector_suspended)
check_hung_uninterruptible_tasks(timeout);
hung_last_checked = jiffies;
continue;
@@ -275,6 +297,10 @@ static int watchdog(void *dummy)
static int __init hung_task_init(void)
{
atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
+
+ /* Disable hung task detector on suspend */
+ pm_notifier(hungtask_pm_notify, 0);
+
watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");

return 0;
--
2.17.1
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