Re: [PATCH RFC] kernel/hung_task.c: disable on suspend

Oleg Nesterov
2018-09-13T15:23:13Z

On 09/13, Rafael J. Wysocki wrote:
>
> On Wed, Sep 12, 2018 at 6:11 PM Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
> >
> > It is possible to observe hung_task complaints when system goes to
> > suspend-to-idle 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
>
> This actually is a good catch, but the problem is related to what
> happens to the monotonic clock during suspend to idle.
>
> The clock issue needs to be addressed anyway IMO and then this problem
> will go away automatically.

I don't understand your discussion with Vitaly, but shouldn't we make
khungtaskd thread freezable anyway?

Oleg.

--- x/kernel/hung_task.c
+++ x/kernel/hung_task.c
@@ -185,7 +185,7 @@ static void check_hung_uninterruptible_t
hung_task_show_lock = false;
rcu_read_lock();
for_each_process_thread(g, t) {
- if (!max_count--)
+ if (!max_count-- || freezing(current))
goto unlock;
if (!--batch_count) {
batch_count = HUNG_TASK_BATCHING;
@@ -249,6 +249,7 @@ static int watchdog(void *dummy)
{
unsigned long hung_last_checked = jiffies;

+ set_freezable();
set_user_nice(current, 0);

for ( ; ; ) {
@@ -266,7 +267,7 @@ static int watchdog(void *dummy)
hung_last_checked = jiffies;
continue;
}
- schedule_timeout_interruptible(t);
+ freezable_schedule_timeout_interruptible(t);
}

return 0;