linux-kernel - Re: [RFC PATCH] ARM64: cmpxchg.h: Clear the exclusive access bit on fail

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Date:	Fri, 27 Feb 2015 10:06:13 +0000
From:	Will Deacon <will.deacon@....com>
To:	Pranith Kumar <bobby.prani@...il.com>
Cc:	Catalin Marinas <Catalin.Marinas@....com>,
	Steve Capper <steve.capper@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] ARM64: cmpxchg.h: Clear the exclusive access bit on
 fail

On Fri, Feb 27, 2015 at 05:46:55AM +0000, Pranith Kumar wrote:
> In cmpxchg(), we do a load exclusive on an address and upon a comparison fail,
> we skip the store exclusive instruction. This can result in the exclusive bit
> still set. If there was a store exclusive after this to the same address, that
> will see the exclusive bit set. This should not happen.

... and the problem with that is?

> We need to clear the exclusive bit in these cases.

Why?

Will
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