From mboxrd@z Thu Jan  1 00:00:00 1970
From: linux@arm.linux.org.uk (Russell King - ARM Linux)
Date: Sun, 20 Feb 2011 13:14:02 +0000
Subject: barriers in mutexes?
In-Reply-To: <4D4ADE2F.50105@codeaurora.org>
References: <4D4A0D7A.9090005@codeaurora.org>
	<20110203110837.GA14627@n2100.arm.linux.org.uk>
	<4D4ADE2F.50105@codeaurora.org>
Message-ID: <20110220131402.GG14495@n2100.arm.linux.org.uk>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Thu, Feb 03, 2011 at 08:56:15AM -0800, Steve Muckle wrote:
> On 02/03/11 03:08, Russell King - ARM Linux wrote:
> > On Wed, Feb 02, 2011 at 06:05:46PM -0800, Steve Muckle wrote:
> >> Looking at kernel/mutex.c and arch/arm/include/asm/mutex.h, it appears
> >> there aren't any memory barriers in the fast path of mutexes. I see this
> >> was discussed here a long time back:
> >>
> >> http://patchwork.kernel.org/patch/25856/
> >>
> >> How was this resolved?
> > 
> > bac4e96 ([ARM] barriers: improve xchg, bitops and atomic SMP barriers)
> 
> The fast path of mutexes on ARM >= v6 doesn't seem to use these
> operations - it's just ldrex/strex. Looking at the v7 ARM ARM it seems
> barriers are still required with ldrex/strex.

Patch welcome.