linux-kernel - Re: [PATCH 1/1] scheduler: access to variable out of scope in sched

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Message-ID: <20090617163723.GB16128@elte.hu>
Date:	Wed, 17 Jun 2009 18:37:23 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Christian Engelmayer <christian.engelmayer@...quentis.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] scheduler: access to variable out of scope in
	sched_slice()


* Christian Engelmayer <christian.engelmayer@...quentis.com> wrote:

> From: Christian Engelmayer <christian.engelmayer@...quentis.com>
> 
> Access to local variable lw is aliased by usage of pointer load. Access to
> pointer load in calc_delta_mine() happens when lw is already out of scope.
> 
> Signed-off-by: Christian Engelmayer <christian.engelmayer@...quentis.com>
> --
> Reported by static code analysis. 
> 
> --- linux-2.6.30/kernel/sched_fair.c.orig	2009-06-16 10:01:50.000000000 +0200
> +++ linux-2.6.30/kernel/sched_fair.c	2009-06-16 10:02:39.000000000 +0200
> @@ -430,12 +430,13 @@ static u64 sched_slice(struct cfs_rq *cf
>  
>  	for_each_sched_entity(se) {
>  		struct load_weight *load;
> +		struct load_weight lw;
>  
>  		cfs_rq = cfs_rq_of(se);
>  		load = &cfs_rq->load;
>  
>  		if (unlikely(!se->on_rq)) {
> -			struct load_weight lw = cfs_rq->load;
> +			lw = cfs_rq->load;
>  
>  			update_load_add(&lw, se->load.weight);
>  			load = &lw;

Good one!

I suspect it doesnt matter in practice because GCC will just have 
them all on the same stack frame?

	Ingo
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