linux-kernel - Re: [PATCH] sched: Fix 32bit race

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Message-ID: <20110712200915.GA7190@linux.vnet.ibm.com>
Date:	Tue, 12 Jul 2011 13:09:15 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Mike Galbraith <efault@....de>, bruno <bruno@...ff.to>
Subject: Re: [PATCH] sched: Fix 32bit race

On Tue, Jul 12, 2011 at 02:07:14PM +0200, Peter Zijlstra wrote:
> Ingo, can we get the below patch into sched/urgent and towards Linus
> before he cuts a release?
> 
> I'm surprised there weren't more 32bit-smp doesn't boot for me
> complaints, either Bruno is a very 'lucky' man, or nobody is using 32bit
> kernels any more since he was hitting this quite reliably.

It appears that there have been several, but they were blaming RCU
instead.  ;-)

> ---
> Subject: sched: Fix 32bit race
> From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Date: Mon Jul 11 16:28:50 CEST 2011
> 
> Commit 3fe1698b7fe0 ("sched: Deal with non-atomic min_vruntime reads
> on 32bit") forgot to initialize min_vruntime_copy which could lead to
> an infinite while loop in task_waking_fair() under some circumstances
> (early boot, lucky timing).

Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

> Reported-and-tested-by: Bruno Wolff III <bruno@...ff.to>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
> Index: linux-2.6/kernel/sched.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched.c
> +++ linux-2.6/kernel/sched.c
> @@ -7750,6 +7750,9 @@ static void init_cfs_rq(struct cfs_rq *c
>  #endif
>  #endif
>  	cfs_rq->min_vruntime = (u64)(-(1LL << 20));
> +#ifndef CONFIG_64BIT
> +	cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
> +#endif
>  }
> 
>  static void init_rt_rq(struct rt_rq *rt_rq, struct rq *rq)
> 
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