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

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Date:	Sun, 2 Dec 2007 16:59:13 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	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

On Mon, 3 Dec 2007 01:07:41 +0100
Andi Kleen <andi@...stfloor.org> wrote:

> > We really need to get better diagnostics for the
> > bad-kernel-behavior-that-is-seen-as-bug cases. If we ever want to
> > get to the scenario where we have a more or less robust measure of
> > kernel quality (and we're not all that far off for several cases),
> > one thing
> 
> One measure to kernel quality is to recover well from IO errors
> (like network problems or broken block devices)

yes. and this patch will flag cases that don't (yet) work well

> 
> This patch will likely work against that by breaking error paths.

it won't break error paths, it will at most put a warning in the log.
It doesn't kill or otherwise damage the system or process.

> 
> > This patch is a step in the right direction there, by quite a
> > lot.
> > 
> > I really don't understand what your objection is to this patch...
> > is it that an enterprise distro can't ship with it on? (Which is
> > fine btw)
> 
> Any distribution aimed at end users cannot ship with it on. 

That's a pretty bold statement; assuming that the TASK_KILLABLE patch
is in, I don't see the problem.

And even if a distro doesn't turn it on, I still don't see a problem;
it's a diagnostics patch that people can turn on (even at runtime) if
they see problems.

> Also in general I have my doubts that the false positive:real bug
> ratio of this warning is well balanced.

I'll just have to disagree with you then; but both of us are making
wild guesses. Only one way to get the real false positive percentage.

> Just consider the original
> example of dead network servers. Even in my relatively small
> home network that that is a quite common occurrence. This patch
> will break that all by throwing random backtraces when this 
> happens.

1) with TASK_KILLABLE that shouldn't happen
2) how does "throwing a backtrace" "break" things?


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