linux-kernel - Re: [PATCH linux-next] mm/hugetlb: fix warning in alloc_huge_page/dequeue_huge_page

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Message-Id: <20120417135726.05de2546.akpm@linux-foundation.org>
Date:	Tue, 17 Apr 2012 13:57:26 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH linux-next] mm/hugetlb: fix warning in
 alloc_huge_page/dequeue_huge_page_vma

On Tue, 17 Apr 2012 16:28:19 +0400
Konstantin Khlebnikov <khlebnikov@...nvz.org> wrote:

> This patch fixes gcc warning (and bug?) introduced in linux-next commit cc9a6c877
> ("cpuset: mm: reduce large amounts of memory barrier related damage v3")
> 
> Local variable "page" can be uninitialized if nodemask from vma policy does not
> intersects with nodemask from cpuset. Even if it wouldn't happens it's better to
> initialize this variable explicitly than to introduce kernel oops on weird corner case.
> 
> mm/hugetlb.c: In function ___alloc_huge_page___:
> mm/hugetlb.c:1135:5: warning: ___page___ may be used uninitialized in this function
> 
> ...
>
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -532,7 +532,7 @@ static struct page *dequeue_huge_page_vma(struct hstate *h,
>  				struct vm_area_struct *vma,
>  				unsigned long address, int avoid_reserve)
>  {
> -	struct page *page;
> +	struct page *page = NULL;
>  	struct mempolicy *mpol;
>  	nodemask_t *nodemask;
>  	struct zonelist *zonelist;

hm, that's a pretty blatant use-uninitialised bug.  I wonder why so few
gcc versions report it.  Mine doesn't.

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