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 10:10:33 +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, Paul, Lai.

On 11/11/2010 05:20 AM, Paul E. McKenney wrote:
> On Wed, Nov 10, 2010 at 04:56:32PM +0800, Lai Jiangshan wrote:
>> On 11/09/2010 09:26 PM, Tejun Heo wrote:
>>> Hello, Paul.
>>>
>>>
>>> How about something like the following?  It's slightly bigger but I
>>> think it's a bit easier to understand.  Thanks.
>>
>> Hello, Paul, Tejun,
>>
>> I think this approach is good and much better when several tasks
>> call synchronize_sched_expedited() at the same time.
> 
> I am becoming more comfortable with it as well.  Tejun, what kind of
> testing did you do?  Lai, could you please run it on your systems?

I just compile tested it (so no SOB).  Please feel free to take it and
shape it into a proper patch.  Oh, I think we can drop both mb()'s at
the top and bottom as both atomic_inc_return() and atomic_cmpxchg()
imply full memory barrier.

Thanks.

-- 
tejun
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