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Date: Wed, 9 Sep 2015 18:31:02 -0500 (CDT)
From: Christoph Lameter <cl@linux.com>
Subject: Re: Is it OK to pass non-acquired objects to kfree?
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To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>, Pekka Enberg <penberg@kernel.org>, David Rientjes <rientjes@google.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Andrew Morton <akpm@linux-foundation.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, Andrey Konovalov <andreyknvl@google.com>, Alexander Potapenko <glider@google.com>

On Wed, 9 Sep 2015, Paul E. McKenney wrote:

> Either way, Dmitry's tool got a hit on real code using the slab
> allocators.  If that hit is a false positive, then clearly Dmitry
> needs to fix his tool, however, I am not (yet) convinced that it is a
> false positive.  If it is not a false positive, we might well need to
> articulate the rules for use of the slab allocators.

Could I get a clear definiton as to what exactly is positive? Was this
using SLAB, SLUB or SLOB?

> > This would all use per cpu data. As soon as a handoff is required within
> > the allocators locks are being used. So I would say no.
>
> As in "no, it is not necessary for the caller of kfree() to invoke barrier()
> in this example", right?

Actually SLUB contains a barrier already in kfree(). Has to be there
because of the way the per cpu pointer is being handled.

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