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

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Date:	Wed, 18 Apr 2012 09:58:31 +0400
From:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.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

Andrew Morton wrote:
> 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.

I'm using latest gcc-4.7

>
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