linux-kernel - Re: [PATCH] sched: fix race in schedule

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Date:	Mon, 10 Mar 2008 14:07:12 -0700
From:	Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	linux-rt-users@...r.kernel.org, hpj@...la.net,
	stable <stable@...nel.org>
Subject: Re: [PATCH] sched: fix race in schedule

Peter Zijlstra wrote:
> On Mon, 2008-03-10 at 13:54 -0700, Hiroshi Shimamoto wrote:
>> Peter Zijlstra wrote:
>>> On Mon, 2008-03-10 at 13:01 -0700, Hiroshi Shimamoto wrote:
>>>
>>>> thanks, your patch looks nice to me.
>>>> I had focused setprio, on_rq=0 and running=1 situation, it makes me to
>>>> fix these functions.
>>>> But one point, I've just noticed. I'm not sure on same situation against
>>>> sched_rt. I think the pre_schedule() of rt has chance to drop rq lock.
>>>> Is it OK?
>>> Ah, you are quite right, that'll teach me to rush out a patch just
>>> because dinner is ready :-). 
>>>
>>> How about we submit the following patch for mainline and CC -stable to
>>> fix .23 and .24:
>> thanks for working, I'm OK, and will test it soon.
>> IIRC, it came from the group scheduling, .23 probably doesn't have this issue.
> 
> Might not have this exact race, but I've checked both .23 and .24, both
> can unlock the rq before we do ->put_prev_task(), leaving a window for
> potential nasties. I'm rather safe than sorry :-)

Ah, you're correct. I haven't gotten out from the first situation yet :-)

thanks,
Hiroshi Shimamoto
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