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Date:   Wed, 27 Jan 2021 22:22:42 +0000
From:   Will Deacon <will@kernel.org>
To:     Alexander A Sverdlin <alexander.sverdlin@nokia.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
        Russell King <linux@armlinux.org.uk>,
        linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 2/2] ARM: mcs_spinlock: Drop smp_wmb in
 arch_mcs_spin_lock_contended()
Message-ID: <20210127222241.GC848@willie-the-truck>
References: <20210127200109.16412-1-alexander.sverdlin@nokia.com>
 <20210127200109.16412-2-alexander.sverdlin@nokia.com>
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On Wed, Jan 27, 2021 at 09:01:09PM +0100, Alexander A Sverdlin wrote:
> From: Alexander Sverdlin <alexander.sverdlin@nokia.com>
> 
> Drop smp_wmb in arch_mcs_spin_lock_contended() after adding in into
> ARCH-independent code.
> 
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
> ---
>  arch/arm/include/asm/mcs_spinlock.h | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/arch/arm/include/asm/mcs_spinlock.h b/arch/arm/include/asm/mcs_spinlock.h
> index 529d2cf..d8fa921 100644
> --- a/arch/arm/include/asm/mcs_spinlock.h
> +++ b/arch/arm/include/asm/mcs_spinlock.h
> @@ -8,8 +8,6 @@
>  /* MCS spin-locking. */
>  #define arch_mcs_spin_lock_contended(lock)				\
>  do {									\
> -	/* Ensure prior stores are observed before we enter wfe. */	\
> -	smp_mb();							\

I think this is the right place for the barrier, not in the core code.

Will