Re: [PATCH][v3] hung_task: Panic after fixed number of hung tasks

[Petr Mladek <pmladek@suse.com>]

On Tue 2025-10-14 13:23:58, Lance Yang wrote:
> Thanks for the patch!
> 
> I noticed the implementation panics only when N tasks are detected
> within a single scan, because total_hung_task is reset for each
> check_hung_uninterruptible_tasks() run.

Great catch!

Does it make sense?
Is is the intended behavior, please?

> So some suggestions to align the documentation with the code's
> behavior below :)

> On 2025/10/12 19:50, lirongqing wrote:
> > From: Li RongQing <lirongqing@baidu.com>
> > 
> > Currently, when 'hung_task_panic' is enabled, the kernel panics
> > immediately upon detecting the first hung task. However, some hung
> > tasks are transient and the system can recover, while others are
> > persistent and may accumulate progressively.

My understanding is that this patch wanted to do:

   + report even temporary stalls
   + panic only when the stall was much longer and likely persistent

Which might make some sense. But the code does something else.

> > --- a/kernel/hung_task.c
> > +++ b/kernel/hung_task.c
> > @@ -229,9 +232,11 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
> >   	 */
> >   	sysctl_hung_task_detect_count++;
> > +	total_hung_task = sysctl_hung_task_detect_count - prev_detect_count;
> >   	trace_sched_process_hang(t);
> > -	if (sysctl_hung_task_panic) {
> > +	if (sysctl_hung_task_panic &&
> > +			(total_hung_task >= sysctl_hung_task_panic)) {
> >   		console_verbose();
> >   		hung_task_show_lock = true;
> >   		hung_task_call_panic = true;

I would expect that this patch added another counter, similar to
sysctl_hung_task_detect_count. It would be incremented only
once per check when a hung task was detected. And it would
be cleared (reset) when no hung task was found.

Best Regards,
Petr