linux-kernel - Re: [PATCH] sched: fix need_resched() when checking peempt

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Message-ID: <BANLkTi=7C1jkKau_Lt7BxJ_PKrzE67incg@mail.gmail.com>
Date:	Wed, 25 May 2011 12:34:23 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Hillf Danton <dhillf@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Mike Galbraith <efault@....de>
Subject: Re: [PATCH] sched: fix need_resched() when checking peempt

On Wed, May 25, 2011 at 11:24 AM, Yong Zhang <yong.zhang0@...il.com> wrote:
> On Tue, May 24, 2011 at 9:50 PM, Hillf Danton <dhillf@...il.com> wrote:
>> On Tue, May 24, 2011 at 9:39 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
>>> On Tue, 2011-05-24 at 21:27 +0800, Hillf Danton wrote:
>>>> When checking if current task could be preempted by a newly woken task,
>>>> further check could be bypassed if the current thread is different from
>>>> the current task of run-queue, and it is corrected accordingly.
>>>
>>> Ug, that change log is an obfuscated mess. But looking at the actual
>>> patch, I figured what you wanted to say. How about this:
>>>
>>> ----
>>> The RT preempt check tests the wrong task if NEED_RESCHED is set. It
>>> currently checks the local CPU task. It is suppose to check the task
>>> that is running on the run queue we are about to wake another task on.
>>> ----
>>>
>> Thanks, it is great changelog:)
>
> Good catch.
>
> Reviewed-by: Yong Zhang <yong.zhang0@...il.com>
>
> BTW, this may be the reason for we could trigger
> WARN_ON_ONCE(test_tsk_need_resched(next));
> https://lkml.org/lkml/2010/12/20/28
>
> Peter, Mike, how do you think about it?

Since rq->lock protects both, that issue needs more digging :)

>
> Thanks,
> Yong
>
>
> --
> Only stand for myself
>



-- 
Only stand for myself
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