linux-kernel - Re: [PROBLEM] 2.6.22-rc2 panics on x86-64 with slub

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Message-ID: <20070522112008.GA16308@elte.hu>
Date:	Tue, 22 May 2007 13:20:11 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Srihari Vijayaraghavan <sriharivijayaraghavan@...oo.com.au>
Cc:	Christoph Lameter <clameter@....com>,
	Hugh Dickins <hugh@...itas.com>,
	Oliver Xymoron <oxymoron@...te.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PROBLEM] 2.6.22-rc2 panics on x86-64 with slub

* Srihari Vijayaraghavan <sriharivijayaraghavan@...oo.com.au> wrote:

> Compiled slub with SMP & CONFIG_PROVE_LOCKING. No luck. It still hangs 
> solid after the second spinlock lockup call trace.

hm. This suggests that the spinlock got corrupted - otherwise lockdep 
would have complained about the lockup before the spinlock-debug code 
had its chance.

> Surprisingly, with CONFIG_SMP=n, CONFIG_PROVE_LOCKING produces this 
> with slub (then hangs solid):

yes - PROVE_LOCKING reactivates spinlocks even on UP. At least this 
suggests that you'd have gotten the hang even with maxcpus=1 - i.e. the 
spinlock corruption is not caused by some genuine SMP race.

furthermore, PROVE_LOCKING also turns on DEBUG_LOCK_ALLOC, so we now 
know that it's most likely not use-after-free type of corruption.

	Ingo
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