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

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Date:	Mon, 3 Dec 2007 11:23:55 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Radoslaw Szkodzinski <lkml@...ralstorm.puszkin.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [feature] automatically detect hung TASK_UNINTERRUPTIBLE tasks


* Radoslaw Szkodzinski <lkml@...ralstorm.puszkin.org> wrote:

> > iirc TASK_KILLABLE fixed NFS only. While that's a good thing there 
> > are unfortunately a lot more subsystems that would need the same 
> > treatment.
> 
> Yes, that's exactly why the patch is needed - to find the bugs and fix 
> them. Otherwise you'll have problems finding some places to convert to 
> TASK_KILLABLE.
> 
> CIFS and similar have to be fixed - it tends to lock the app using it, 
> in unkillable state.

Amen. I still have to see a single rational argument against this 
debugging feature - and tons of arguments were listed in favor of it. So 
let's just try and see what happens.

> > Yes let's break things first instead of looking at the implications 
> > closely.
> 
> Throwing _rare_ stack traces is not breakage. 120s 
> task_uninterruptible in the usual case (no errors) is already broken - 
> there are no sane loads that can invoke that IMO.
> 
> A stack trace on x subsystem error is not that bad, especially as 
> these are limited to 10 per session.

we could lower that limit to 1 per bootup - if they become annoying. 
There's lots of flexibility in the code. Really, we should have done 
this 10 years ago - it would have literally saved me many days of 
debugging time combined, and i really have experience in identifying 
such bad tasks. (and it would have sped up debugging in countless number 
of instances when users were met with an uninterruptible task.)

	Ingo
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