linux-kernel - Re: [tip:sched/urgent] sched/fair: Avoid using uninitialized variable in preferred_group

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Date:	Mon, 09 Feb 2015 11:41:19 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Peter Zijlstra" <peterz@...radead.org>,
	"Ingo Molnar" <mingo@...nel.org>
Cc:	<tglx@...utronix.de>, <torvalds@...ux-foundation.org>,
	<riel@...hat.com>, <linux-kernel@...r.kernel.org>, <hpa@...or.com>
Subject: Re: [tip:sched/urgent] sched/fair:  Avoid using uninitialized
 variable in preferred_group_nid()

>>> On 09.02.15 at 12:37, <peterz@...radead.org> wrote:
> On Mon, Feb 09, 2015 at 09:21:15AM +0100, Ingo Molnar wrote:
>> Ok, agreed, please send a separate patch to fix this.
> 
> Jan, I didn't want to put your SoB on without feedback, holler and I'll
> amend it any way you like.

It's perfectly fine to add it.

Jan

> ---
> Subject: sched/numa: Avoid some pointless iterations
> From: Jan Beulich <JBeulich@...e.com>
> Date: Mon Feb  9 12:30:00 CET 2015
> 
> Commit 81907478c431 ("sched/fair: Avoid using uninitialized variable
> in preferred_group_nid()") unconditionally initializes max_group with
> NODE_MASK_NONE, this means that when !max_faults (max_group didn't get
> set), we'll now continue the iteration with an empty mask.
> 
> Which in turn makes the actual body of the loop go away, so we'll just
> iterate until completion; short circuit this by breaking out of the
> loop as soon as this would happen.
> 
> Maybe-Signed-off-by: Jan Beulich <jbeulich@...e.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  kernel/sched/fair.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1763,6 +1763,8 @@ static int preferred_group_nid(struct ta
>  			}
>  		}
>  		/* Next round, evaluate the nodes within max_group. */
> +		if (!max_faults)
> +			break;
>  		nodes = max_group;
>  	}
>  	return nid;



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