linux-kernel - Re: smp_call_function

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Message-ID: <20150402182607.GA8896@gmail.com>
Date:	Thu, 2 Apr 2015 20:26:07 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Chris J Arges <chris.j.arges@...onical.com>,
	Rafael David Tinoco <inaddy@...ntu.com>,
	Peter Anvin <hpa@...or.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Gema Gomez <gema.gomez-solano@...onical.com>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: smp_call_function_single lockups


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> So unless we find a real clear signature of the bug (I was hoping 
> that the ISR bit would be that sign), I don't think trying to bisect 
> it based on how quickly you can reproduce things is worthwhile.

So I'm wondering (and I might have missed some earlier report that 
outlines just that), now that the possible location of the bug is 
again sadly up to 15+ million lines of code, I have no better idea 
than to debug by symptoms again: what kind of effort was made to 
examine the locked up state itself?

Softlockups always have some direct cause, which task exactly causes 
scheduling to stop altogether, why does it lock up - or is it not a 
clear lockup, just a very slow system?

Thanks,

	Ingo
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