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

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Message-ID: <4AFEAB6D.60600@redhat.com>
Date:	Sat, 14 Nov 2009 15:06:53 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Tejun Heo <tj@...nel.org>, 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 11/13/2009 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.
>    

Definitely.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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