linux-kernel - Re: [PATCH] sched: fix to use invalid sched

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Message-ID: <20070919213715.GA14086@elte.hu>
Date:	Wed, 19 Sep 2007 23:37:15 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] sched: fix to use invalid sched_class


* Hiroshi Shimamoto <h-shimamoto@...jp.nec.com> wrote:

> Hi Ingo,
> 
> I found an issue about the scheduler.
> If you need a test case, please let me know.
> Here is a patch.
> 
> When using rt_mutex, a NULL pointer dereference is occurred at
> enqueue_task_rt. Here is a scenario;
> 1) there are two threads, the thread A is fair_sched_class and
>    thread B is rt_sched_class.
> 2) Thread A is boosted up to rt_sched_class, because the thread A
>    has a rt_mutex lock and the thread B is waiting the lock.
> 3) At this time, when thread A create a new thread C, the thread
>    C has a rt_sched_class.
> 4) When doing wake_up_new_task() for the thread C, the priority
>    of the thread C is out of the RT priority range, because the
>    normal priority of thread A is not the RT priority. It makes
>    data corruption by overflowing the rt_prio_array.
> The new thread C should be fair_sched_class.
> 
> The new thread should be valid scheduler class before queuing.
> This patch fixes to set the suitable scheduler class.

Nice fix! It's a 2.6.23 must-have fix - i'll push it out into the 
scheduler tree. Thanks!

	Ingo
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