linux-kernel - Re: [feature] automatically detect hung TASK

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Date:	Mon, 3 Dec 2007 23:47:36 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, andi@...stfloor.org,
	penberg@...helsinki.fi, lkml@...ralstorm.puszkin.org,
	arjan@...radead.org, linux-kernel@...r.kernel.org,
	tglx@...utronix.de
Subject: Re: [feature] automatically detect hung TASK_UNINTERRUPTIBLE tasks

On Monday, 3 of December 2007, Ingo Molnar wrote:
> 
> * Rafael J. Wysocki <rjw@...k.pl> wrote:
> 
> > > This feature will save one full reporter-developer round-trip during 
> > > investigation of a significant number of bug reports.
> > > 
> > > It might be more practical if it were to dump the traces for _all_ 
> > > D-state processes when it fires - basically an auto-triggered 
> > > sysrq-W.
> > 
> > Er, it won't play well if that happen when tasks are frozen for 
> > suspend.
> 
> right now any suspend attempt times out after 20 seconds:
> 
>   $ grep TIMEOUT kernel/power/process.c
>   #define TIMEOUT (20 * HZ)
>           end_time = jiffies + TIMEOUT;

This is the timeout for freezing tasks, but if the freezing succeeds, they
can stay in TASK_UNINTERRUPTIBLE for quite some more time, especially during
a hibernation (the tasks stay frozen until we power off the system after saving
the image).

> which should be well before the 120 seconds timeout that the detector 
> uses. But indeed you are right in that the refrigerator() works via 
> TASK_UNINTERRUPTIBLE too. I've updated the patch to exclude PF_FROZEN - 
> attached below. That should solve this particular issue, even if the 
> timeout increased to above 20 secs, right?

Sure.

Thanks,
Rafael
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