From mboxrd@z Thu Jan  1 00:00:00 1970
From: Waiman Long <waiman.long@hp.com>
Subject: Re: [PATCH v10 1/4] qrwlock: A queue read/write lock implementation
Date: Thu, 23 Jan 2014 12:47:20 -0500
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, Arnd Bergmann <arnd@arndb.de>, "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>, the arch/x86 maintainers <x86@kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Steven Rostedt <rostedt@goodmis.org>, Andrew Morton <akpm@linux-foundation.org>, Michel Lespinasse <walken@google.com>, Andi Kleen <andi@firstfloor.org>, Rik van Riel <riel@redhat.com>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>, George Spelvin <linux@horizon.com>, Tim Chen <tim.c.chen@linux.intel.com>, "Chandramouleeswaran, Aswin" <aswin@hp.com>, Scott J Norton <scott.norton@hp.com>
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On 01/23/2014 12:15 PM, Linus Torvalds wrote:
> On Thu, Jan 23, 2014 at 9:12 AM, Waiman Long<waiman.long@hp.com>  wrote:
>> I thought that all atomic RMW instructions are memory barrier.
> On x86 they are. Not necessarily elsewhere.
>
>> If they are not, what kind of barrier should be added?
> smp_mb__before_atomic_xyz() and smp_mb__after_atomic_xyz() will do it,
> and are no-op (well, barriers - I don't think it matters) on x86.
>
>              Linus
> -

Thank for the info. I am less familiar with that kind of issues on other 
architecture. I will add a smp_mb__after_atomic_dec() & send out a new 
patch.

-Longman