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Message-ID: <1437171254.28088.87.camel@kernel.crashing.org>
Subject: Re: [RFC PATCH v2] memory-barriers: remove
 smp_mb__after_unlock_lock()
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Will Deacon <will.deacon@arm.com>
Cc: "paulmck@linux.vnet.ibm.com" <paulmck@linux.vnet.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>
Date: Sat, 18 Jul 2015 08:14:14 +1000
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On Fri, 2015-07-17 at 10:32 +0100, Will Deacon wrote:
>  static inline void arch_spin_unlock(arch_spinlock_t *lock)
>  {
> -       SYNC_IO;
> -       __asm__ __volatile__("# arch_spin_unlock\n\t"
> -                               PPC_RELEASE_BARRIER: : :"memory");
> +       smp_mb();
>         lock->slock = 0;
>  }

That probably needs to be mb() in case somebody has the expectation that
it does a barrier vs. DMA on UP.

Cheers,
Ben.