[ 116/147] mm: hugetlb: fix pgoff computation when unmapping page from vma

[Ben Hutchings]

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Hillf Danton <dhillf@xxxxxxxxx>

commit 0c176d52b0b2619f231b2bbf329b90c028134f58 upstream.

The computation for pgoff is incorrect, at least with

	(vma->vm_pgoff >> PAGE_SHIFT)

involved.  It is fixed with the available method if HPAGE_SIZE is
concerned in page cache lookup.

[akpm@xxxxxxxxxxxxxxxxxxxx: use vma_hugecache_offset() directly, per Michal]
Signed-off-by: Hillf Danton <dhillf@xxxxxxxxx>
Cc: Mel Gorman <mel@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 mm/hugetlb.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2429,8 +2429,7 @@ static int unmap_ref_private(struct mm_s
 	 * from page cache lookup which is in HPAGE_SIZE units.
 	 */
 	address = address & huge_page_mask(h);
-	pgoff = ((address - vma->vm_start) >> PAGE_SHIFT)
-		+ (vma->vm_pgoff >> PAGE_SHIFT);
+	pgoff = vma_hugecache_offset(h, vma, address);
 	mapping = vma->vm_file->f_dentry->d_inode->i_mapping;
 
 	/*


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