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Date: Fri, 19 Aug 2016 16:01:06 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
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        Andrew Morton <akpm@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Susanne Spraul <1vier1@web.de>, parri.andrea@gmail.com
Subject: Re: spin_lock implicit/explicit memory barrier
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On Fri, Aug 12, 2016 at 10:59:46AM +0800, Boqun Feng wrote:
> But if an arch implements its spin_lock() with a full barrier, even
> though the atomic is implemented by ll/sc, the STORE part of which can't
> be reordered with memory operations in the critcal sections. I think
> maybe that's the case for alpha(and also for ARM32).

Correct, Alpha only has a full fence and uses that after the ll/sc to
provide acquire semantics, ARM has other barriers but too uses a full
barrier here.