linux-kernel - Re: [PATCH] sched: fix rt_nr_migratory corruption raised in push_rt

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Message-ID: <1306894886.4791.23.camel@marge.simson.net>
Date:	Wed, 01 Jun 2011 04:21:26 +0200
From:	Mike Galbraith <efault@....de>
To:	Hillf Danton <dhillf@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Yong Zhang <yong.zhang0@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] sched: fix rt_nr_migratory corruption raised in
 push_rt_task()

On Tue, 2011-05-31 at 21:56 +0800, Hillf Danton wrote:
> On Tue, May 31, 2011 at 3:36 PM, Mike Galbraith <efault@....de> wrote:
> > On Mon, 2011-05-30 at 21:39 +0800, Hillf Danton wrote:
> >> When pushing, if a pushable task could not be pushed, it is dequeued with no
> >> updating the rt_nr_migratory element of RT run-queue, then rt_nr_migratory is
> >> corrupted, which is fixed by removing the dequeue operation.
> >
> > Hm.  I think you're right that this dequeue_pushable_task() call can be
> > removed, at least I didn't see it's reason for existing.  I'd word it a
> > bit differently though, and not return 1 unless we really did push.
> >
> 
> Hi Mike
> 
> Your message shows what is called professional work, but something lost,
> 
> > From: Hillf Danton <dhillf@...il.com>
> >
> > sched, rt: fix rq->rt.pushable_tasks bug in push_rt_task()
> >
> > Do not call dequeue_pushable_task() when failing to push an eligible
> > task, as it remains pushable, merely not at this particular moment.
> >
> > Signed-off-by: Hillf Danton <dhillf@...il.com>
> 
> Signed-off-by: Mike Galbraith <efault@....de>
> 
> right?

Well, you did the legwork, but I resent it as requested.

> > ---
> >  kernel/sched_rt.c |   15 ++++++++-------
> >  1 file changed, 8 insertions(+), 7 deletions(-)
> >
> > Index: linux-2.6.40.git/kernel/sched_rt.c
> > ===================================================================
> 
> And how to drive git to print the above two lines?

That's easy, I used quilt :)  I'm no master of git-fu (wimpy whitebelt),
use git for hunting, but quilt for twiddling.

	-Mike

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