linux-kernel - Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release semantics) causing failures on arm64 (ThunderX)

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Message-ID: <56732E8D.8050706@arm.com>
Date:	Thu, 17 Dec 2015 15:52:13 -0600
From:	Jeremy Linton <jeremy.linton@....com>
To:	Will Deacon <will.deacon@....com>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Davidlohr Bueso <dbueso@...e.de>,
	Andrew Pinski <andrew.pinski@...iumnetworks.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release
 semantics) causing failures on arm64 (ThunderX)

On 12/11/2015 06:04 AM, Will Deacon wrote:
> I think Andrew meant the atomic_xchg_acquire at the start of osq_lock,
> as opposed to "compare and swap". In which case, it does look like
> there's a bug here because there is nothing to order the initialisation
> of the node fields with publishing of the node, whether that's
> indirectly as a result of setting the tail to the current CPU or
> directly as a result of the WRITE_ONCE.
>
> Andrew, David: does making that atomic_xchg_acquire and atomic_xchg
> fix things for you?
>
> I don't fully grok what 81a43adae3b9 has to do with any of this, so
> maybe there's another bug too.

Will,

I ran into this problem while getting a machine to boot with ACPI
yesterday. Your suggested fix works on that machine.

Thanks, so for that patch.

Tested-by: Jeremy Linton <jeremy.linton@....com>






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