linux-kernel - Re: [PATCH] time: Add locking to xtime access in get

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Message-ID: <m2mxj2yy5c.fsf@firstfloor.org>
Date:	Wed, 04 May 2011 14:05:35 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Max Asbock <masbock@...ux.vnet.ibm.com>
Cc:	John Stultz <john.stultz@...aro.org>,
	lkml <linux-kernel@...r.kernel.org>,
	John Stultz <johnstul@...ibm.com>,
	Paul Mackerras <paulus@...ba.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Anton Blanchard <anton@...ba.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] time: Add locking to xtime access in get_seconds()

Max Asbock <masbock@...ux.vnet.ibm.com> writes:

> On Tue, 2011-05-03 at 20:11 -0700, John Stultz wrote:
>> From: John Stultz <johnstul@...ibm.com>
>> 
>> So get_seconds() has always been lock free, with the assumption
>> that accessing a long will be atomic.
>> 
>
> get_seconds() is used in the x86 machine check handler and there is a
> comment saying:
> /* We hope get_seconds stays lockless */
>
> This needs to be carefully looked at if locking is introduced to
> get_seconds().

Yes the seqlock being interrupted by an MCE would deadlock.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only
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