linux-kernel - Re: [RFC][PATCH 1/4] sched: Fix a race between __kthread_bind() and sched

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Message-ID: <20150515155653.GA23692@htj.duckdns.org>
Date:	Fri, 15 May 2015 11:56:53 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, riel@...hat.com, dedekind1@...il.com,
	linux-kernel@...r.kernel.org, mgorman@...e.de, rostedt@...dmis.org,
	juri.lelli@....com, Oleg Nesterov <oleg@...hat.com>
Subject: Re: [RFC][PATCH 1/4] sched: Fix a race between __kthread_bind() and
 sched_setaffinity()

On Fri, May 15, 2015 at 05:43:34PM +0200, Peter Zijlstra wrote:
> Because sched_setscheduler() checks p->flags & PF_NO_SETAFFINITY
> without locks, a caller might observe an old value and race with the
> set_cpus_allowed_ptr() call from __kthread_bind() and effectively undo
> it.
> 
> 	__kthread_bind()
> 	  do_set_cpus_allowed()
> 						<SYSCALL>
> 						  sched_setaffinity()
> 						    if (p->flags & PF_NO_SETAFFINITIY)
> 						    set_cpus_allowed_ptr()
> 	  p->flags |= PF_NO_SETAFFINITY
> 
> Fix the issue by putting everything under the regular scheduler locks.
> 
> This also closes a hole in the serialization of
> task_struct::{nr_,}cpus_allowed.
> 
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

For workqueue part,

 Acked-by: Tejun Heo <tj@...nel.org>

Please route anyway you see fit.

Thanks.

-- 
tejun
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