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Date: Mon, 12 Dec 2011 09:56:30 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Ming Lei <tom.leiming@...il.com>
Cc: gregkh@...e.de, akpm@...ux-foundation.org,
linux-kernel@...r.kernel.org, ostrikov@...dia.com,
adobriyan@...il.com, eric.dumazet@...il.com, mingo@...e.hu,
Oliver Neukum <oneukum@...e.de>
Subject: Re: [PATCH 3/3] kref: Remove the memory barriers
On Mon, 2011-12-12 at 11:48 +0800, Ming Lei wrote:
> > LOCK
> > obj = lookup(); /* lets assume obj != NULL */
> > kref_get(&obj->ref);
> > UNLOCK
> >
> > value = obj->member;
> >
> > kref_put(&obj->ref);
> >
> > Now, under our memory model, the read from obj->member can both happen,
> > or be observed to happen before the increment from kref_get() is
> > processed.
>
> It should be the problem if another CPU observed that write/read obj
> is done before kref_get.
WHY?!?!?!
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