linux-kernel - Re: [PATCH 2.6.32-rc6] sched, kvm: fix race condition involving sched_in_preempt

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Message-ID: <4B138BC8.3090008@kernel.org>
Date:	Mon, 30 Nov 2009 18:09:28 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Avi Kivity <avi@...hat.com>
CC:	Ingo Molnar <mingo@...e.hu>, lkml <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 2.6.32-rc6] sched, kvm: fix race condition involving sched_in_preempt_notifers

On 11/14/2009 10:06 PM, Avi Kivity wrote:
> On 11/13/2009 11:55 AM, Ingo Molnar wrote:
>> * Tejun Heo<tj@...nel.org>  wrote:
>>> In finish_task_switch(), fire_sched_in_preempt_notifiers() is called
>>> after finish_lock_switch().  However, depending on architecture,
>>> preemption can be enabled after finish_lock_switch() which breaks the
>>> semantics of preempt notifiers.  Move it before finish_arch_switch().
>>> This also makes in notifiers symmetric to out notifiers in terms of
>>> locking - now both are called under rq lock.
>>>
>>>      
>> I'd like to have Avi's Ack for it,
> 
> Acked-by: Avi Kivity <avi@...hat.com>
> 
>>   but we want to do sched.c changes via
>> the scheduler tree.

So, this one was a bust.  Given that the only platform which might
have been affected by the original bug is ia64 and it's very unlikely
to happen.  I think reverting this from sched/urgent would be the
right thing to do at this point if the branch is headed for another
push to Linus.  Avi, what do you think?

Thanks.

-- 
tejun
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