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Date: Mon, 12 Dec 2011 18:10:31 +0800
From: Ming Lei <tom.leiming@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
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, Dec 12, 2011 at 4:56 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> 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?!?!?!
I did't say the reason because it is same with the example I explained in
the same reply. So if you can make me enlightened on this example,
all will be OK, :-)
thanks,
--
Ming Lei
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