[PATCH linux-next] mm/hugetlb: fix warning in alloc_huge_page/dequeue_huge_page_vma

[PATCH linux-next] mm/hugetlb: fix warning in alloc_huge_page/dequeue_huge_page_vma

[Konstantin Khlebnikov]

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 a??alloc_huge_pagea??:
mm/hugetlb.c:1135:5: warning: a??pagea?? may be used uninitialized in this function

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Mel Gorman <mgorman@suse.de>
---
 mm/hugetlb.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 4314a88..dcf4a55 100644
--- 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;

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

[Mel Gorman]

On Tue, Apr 17, 2012 at 04:28:19PM +0400, Konstantin Khlebnikov 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
> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
> Cc: Mel Gorman <mgorman@suse.de>

Acked-by: Mel Gorman <mgorman@suse.de>

-- 
Mel Gorman
SUSE Labs

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

[David Rientjes]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 848 bytes --]

On Tue, 17 Apr 2012, Konstantin Khlebnikov 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 a??alloc_huge_pagea??:
> mm/hugetlb.c:1135:5: warning: a??pagea?? may be used uninitialized in this function
> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
> Cc: Mel Gorman <mgorman@suse.de>

Acked-by: David Rientjes <rientjes@google.com>

This isn't just in -next, it's also in Linus' tree and seems like 3.4-rc4 
material to me.

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

[Andrew Morton]

On Tue, 17 Apr 2012 16:28:19 +0400
Konstantin Khlebnikov <khlebnikov@openvz.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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Re: [PATCH linux-next] mm/hugetlb: fix warning in alloc_huge_page/dequeue_huge_page_vma

[Konstantin Khlebnikov]

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