linux-kernel - Re: [PATCH] avoid race condition in pick_next_task_fair in kernel/sched

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Message-ID: <1277811316.1868.40.camel@laptop>
Date:	Tue, 29 Jun 2010 13:35:16 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	shenghui <crosslonelyover@...il.com>
Cc:	kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
	mingo@...e.hu, Greg KH <greg@...ah.com>
Subject: Re: [PATCH] avoid race condition in pick_next_task_fair in 
 kernel/sched_fair.c

On Tue, 2010-06-29 at 19:24 +0800, shenghui wrote:

> I wonder is there any chance set_next_entity() can get NULL for
> parameter se if so?

Well, if your machine crashes that way, maybe, but I haven't seen that
happen in a long while.

> And will you please give me some instructions on where rq->lock
> is required?

Pretty much everywhere, if you look at sched.c the only sched_class
method not called with rq->lock held is ::task_fork().

The interesting bits are that schedule()->pre_schedule()/idle_balance()
can drop rq->lock as well as ->select_task_rq().



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