Date: Mon, 3 Dec 2007 11:23:55 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Radoslaw Szkodzinski <lkml@astralstorm.puszkin.org>
Cc: Andi Kleen <andi@firstfloor.org>, Arjan van de Ven <arjan@infradead.org>,
       linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
       Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [feature] automatically detect hung TASK_UNINTERRUPTIBLE tasks
Message-ID: <20071203102355.GC30050@elte.hu>
References: <20071202185945.GA25990@elte.hu> <20071202114152.3bf4332d@laptopd505.fenrus.org> <20071202200953.GA23994@one.firstfloor.org> <20071202202602.GA16480@elte.hu> <20071202204725.GA25891@one.firstfloor.org> <20071202144331.6abf1289@laptopd505.fenrus.org> <20071203000741.GB26636@one.firstfloor.org> <20071202165913.3eaebee6@laptopd505.fenrus.org> <20071203095501.GB28560@one.firstfloor.org> <20071203111520.33ed2139@astralstorm.puszkin.org>
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* Radoslaw Szkodzinski <lkml@astralstorm.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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