linux-kernel - Re: RFC: mutex: hung tasks on SMP platforms with asm-generic/mutex-xchg.h

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Message-ID: <20120807173810.GE16877@mudshark.cambridge.arm.com>
Date:	Tue, 7 Aug 2012 18:38:10 +0100
From:	Will Deacon <will.deacon@....com>
To:	Nicolas Pitre <nico@...xnic.net>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Chris Mason <chris.mason@...ionio.com>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: RFC: mutex: hung tasks on SMP platforms with
 asm-generic/mutex-xchg.h

On Tue, Aug 07, 2012 at 06:33:44PM +0100, Will Deacon wrote:
> What I think is happening is that B writes the -1 in __mutex_lock_common
> and, after seeing a NULL owner (C may not have set that yet), drops through
> to the:
> 
> 	if (atomic_xchg(&lock->count, -1) == 1)
> 		goto done;

Sorry, should have proofread that. I meant to say:

 What I think is happening is that B writes the -1 in __mutex_lock_common
 after seeing a NULL owner (C may not have set that yet) and dropping through
 to the:
 
 	if (atomic_xchg(&lock->count, -1) == 1)
 		goto done;
 

Will
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