linux-kernel - Re: [PATCH 34/34] mm/hugetlb: fix warning in alloc_huge_page/dequeue_huge_page

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Date:	Thu, 19 Jul 2012 22:53:28 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Jonathan Nieder <jrnieder@...il.com>
Cc:	Stable <stable@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 34/34] mm/hugetlb: fix warning in
 alloc_huge_page/dequeue_huge_page_vma

On Thu, Jul 19, 2012 at 03:25:44PM -0500, Jonathan Nieder wrote:
> Hi,
> 
> Mel Gorman wrote:
> 
> > From: Konstantin Khlebnikov <khlebnikov@...nvz.org>
> >
> > Stable note: Not tracked in Bugzilla. [get|put]_mems_allowed() is extremely
> > 	expensive and severely impacted page allocator performance. This
> > 	is part of a series of patches that reduce page allocator overhead.
> >
> > Fix a gcc warning (and bug?) introduced in cc9a6c877 ("cpuset: mm: reduce
> > large amounts of memory barrier related damage v3")
> 
> I know the corresponding upstream commit was alluded to in the cover
> letter, but please also mention it by name in the patch description.

Whoops, yes of course. Most of the patches were imported by a script and
I added notes afterwards. This was one of the few ones I manally
imported and managed to mess it up. Here is a revised version with the
upstream commit included.

---8<---
From: Konstantin Khlebnikov <khlebnikov@...nvz.org>
Date: Wed, 25 Apr 2012 16:01:46 -0700
Subject: [PATCH 34/34] mm/hugetlb: fix warning in alloc_huge_page/dequeue_huge_page_vma

commit b1c12cbcd0a02527c180a862e8971e249d3b347d upstream.

Stable note: Not tracked in Bugzilla. [get|put]_mems_allowed() is extremely
	expensive and severely impacted page allocator performance. This
	is part of a series of patches that reduce page allocator overhead.

Fix a gcc warning (and bug?) introduced in cc9a6c877 ("cpuset: mm: reduce
large amounts of memory barrier related damage v3")

Local variable "page" can be uninitialized if the nodemask from vma policy
does not intersects with nodemask from cpuset.  Even if it doesn't happens
it is better to initialize this variable explicitly than to introduce
a kernel oops in a 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@...nvz.org>
Acked-by: Mel Gorman <mgorman@...e.de>
Acked-by: David Rientjes <rientjes@...gle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@...e.de>
---
 mm/hugetlb.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 64f2b7a..ae60a53 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -454,7 +454,7 @@ 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;
-- 
1.7.9.2

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