linux-kernel - Re: [PATCH, v2] Fix potentially derefencing uninitialized 'r'.

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Date:	Thu, 29 Mar 2012 14:25:42 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Geunsik Lim <geunsik.lim@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Yinghai Lu <yinghai@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH, v2] Fix potentially derefencing uninitialized 'r'.

On Tue 21-02-12 17:58:23, Geunsik Lim wrote:
> From: Geunsik Lim <geunsik.lim@...sung.com>

The warning seems to be bogus. The only caller is for_each_mem_pfn_range
and even if we had type->cnt == 0 we would return before accessing r.
I guess it would be more reasonable to silent the warning by
__maybe_unused.

> 
> v2: reorganize the code with better way to avoid compilation warning
> via the comment of Andrew Morton.
> 
> v1: struct memblock_region 'r' will not be initialized potentially
> because of while() condition in __next_mem_pfn_range()function.
> Solve the compilation warning related problem by initializing
> r data structure.
> 
> Signed-off-by: Geunsik Lim <geunsik.lim@...sung.com>
> ---
>  mm/memblock.c |    8 ++++++--
>  1 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 77b5f22..b8c40c5 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -673,14 +673,18 @@ void __init_memblock __next_mem_pfn_range(int *idx, int nid,
>  	struct memblock_type *type = &memblock.memory;
>  	struct memblock_region *r;
>  
> -	while (++*idx < type->cnt) {
> +	do {
>  		r = &type->regions[*idx];
>  
> +	   if (++*idx < type->cnt) {
>  		if (PFN_UP(r->base) >= PFN_DOWN(r->base + r->size))
>  			continue;
>  		if (nid == MAX_NUMNODES || nid == r->nid)
>  			break;
> -	}
> +	   } else
> +		break;
> +	} while (1);
> +
>  	if (*idx >= type->cnt) {
>  		*idx = -1;
>  		return;
> -- 
> 1.7.8.1
> 
> --
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-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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