linux-kernel - Re: lockdep complaints in slab allocator

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Message-Id: <1259005814.15619.14.camel@penberg-laptop>
Date:	Mon, 23 Nov 2009 21:50:14 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Peter Zijlstra <peterz@...radead.org>, paulmck@...ux.vnet.ibm.com,
	linux-mm@...ck.org, mpm@...enic.com,
	LKML <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: lockdep complaints in slab allocator

On Mon, 23 Nov 2009, Pekka Enberg wrote:
> > That turns out to be _very_ hard. How about something like the following
> > untested patch which delays slab_destroy() while we're under nc->lock.

On Mon, 2009-11-23 at 13:30 -0600, Christoph Lameter wrote:
> Code changes to deal with a diagnostic issue?

OK, fair enough. If I suffer permanent brain damage from staring at the
SLAB code for too long, I hope you and Matt will chip in to pay for my
medication.

I think I was looking at the wrong thing here. The problem is in
cache_free_alien() so the comment in slab_destroy() isn't relevant.
Looking at init_lock_keys() we already do special lockdep annotations
but there's a catch (as explained in a comment on top of
on_slab_alc_key):

 * We set lock class for alien array caches which are up during init.
 * The lock annotation will be lost if all cpus of a node goes down and
 * then comes back up during hotplug

Paul said he was running CPU hotplug so maybe that explains the problem?

			Pekka

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