linux-kernel - Re: [uml-devel] [PATCH 5/6] slab: Annotate slab

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Date:	Wed, 3 Sep 2008 12:40:51 +0300
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Steve VanDeBogart" <vandebo-lkml@...dbox.net>
Cc:	user-mode-linux-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ibm.com>,
	"Ingo Molnar" <mingo@...e.hu>, dkegel@...gle.com,
	jiayingz@...gle.com, "John Reiser" <jreiser@...wagon.com>
Subject: Re: [uml-devel] [PATCH 5/6] slab: Annotate slab

On Wed, Sep 3, 2008 at 12:27 PM, Pekka Enberg <penberg@...helsinki.fi> wrote:
> On Wed, Sep 3, 2008 at 8:08 AM, Steve VanDeBogart
> <vandebo-lkml@...dbox.net> wrote:
>> Ideally, we'd tell Valgrind that the bytes of a free'd slab object are
>> no longer accessible, but the initialized state should remain the same
>> until the object is made accessible again by the next allocation of
>> the object.  Unfortunately, the compression method for A & V bits in
>> Valgrind doesn't allow a region to be inaccessible and retain validness
>> bits.
>
> I don't see why you should mark them initialized all the time. Just
> mark them as uninitialized on kmem_cache_free() and again as
> initialized when they're about to be returned from kmem_cache_alloc()
> like we do in kmemcheck.

Btw, actually, we don't mark them as uninitialized at the moment, but
that's a bug in kmemcheck.
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