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

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Message-ID: <m2oc3jxgtt.fsf@firstfloor.org>
Date:	Tue, 03 May 2011 20:52:46 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	John Stultz <john.stultz@...aro.org>
Cc:	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()

John Stultz <john.stultz@...aro.org> writes:

> From: John Stultz <johnstul@...ibm.com>
>
> So get_seconds() has always been lock free, with the assumption
> that accessing a long will be atomic.
>
> However, recently I came across an odd bug where time() access could
> occasionally be inconsistent, but only on power7 hardware. The

Shouldn't a single rmb() be enough to avoid that?

If not then I suspect there's a lot more code buggy on that CPU than
just the time.

-Andi

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