linux-kernel - Re: [PATCH RFC tip/core/rcu 11/12] rcu: fix race condition in synchronize_sched

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Date:	Thu, 11 Nov 2010 13:52:12 +0100
From:	Tejun Heo <tj@...nel.org>
To:	paulmck@...ux.vnet.ibm.com
CC:	Lai Jiangshan <laijs@...fujitsu.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com
Subject: Re: [PATCH RFC tip/core/rcu 11/12] rcu: fix race condition in synchronize_sched_expedited()

Hello,

On 11/11/2010 01:31 PM, Paul E. McKenney wrote:
> Actually, the memory barriers are still one source of discomfort to me.
> I am concerned about the path out of the function that skips the
> atomic_cmpxchg(), which seem to happen if some concurrent invocation
> advances the "done" counter past us before we get around to checking it.
> I agree on the atomic_inc_return() upon entry to the function, though.

Oooh, you're right.  It needs to be smp_mb().  We can put it right
before break but I don't think it would worth the ugliness.

> And this is going to need some serious testing either way.  ;-)

Definitely.  This is a scary piece of code.  :-)

-- 
tejun
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