linux-kernel - Re: lockdep reports about recursive locking in kmemleak

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Date:	Wed, 9 May 2012 09:05:54 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Pekka Enberg <penberg@...nel.org>
cc:	Catalin Marinas <catalin.marinas@....com>,
	Andrey Vagin <avagin@...nvz.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: lockdep reports about recursive locking in kmemleak

On Wed, 9 May 2012, Pekka Enberg wrote:

> > I'm not sure what the right fix is (cc'ing Christoph for the slab.c
> > code). The lockdep warning is not in kmemleak, it just happens that
> > cache_flusharray() (holding an l3->list_lock) triggers a new allocation
> > via debug_object_activate() and kmemleak also tries to allocate its
> > metadata, causing a cache_alloc_refill() call which acquires a
> > different l3->list_lock, hence the lockdep warning.
>
> How do we know it's always a different nodelist ("l3")?

The second l3 is from a cache that makes no use of "off-slab" secondary
slabs otherwise we would have a bad case of recursion.

If you mark the locks of caches with off-slab features differently from
the simple ones then we should be fine.
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