linux-kernel - [ 117/147] hugetlb: do not use vma_hugecache_offset() for vma_prio_tree

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Message-Id: <20121014143549.569389596@decadent.org.uk>
Date:	Sun, 14 Oct 2012 15:37:30 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Michal Hocko <mhocko@...e.cz>, Hillf Danton <dhillf@...il.com>,
	Mel Gorman <mel@....ul.ie>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [ 117/147] hugetlb: do not use vma_hugecache_offset() for vma_prio_tree_foreach

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

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

From: Michal Hocko <mhocko@...e.cz>

commit 36e4f20af833d1ce196e6a4ade05dc26c44652d1 upstream.

Commit 0c176d52b0b2 ("mm: hugetlb: fix pgoff computation when unmapping
page from vma") fixed pgoff calculation but it has replaced it by
vma_hugecache_offset() which is not approapriate for offsets used for
vma_prio_tree_foreach() because that one expects index in page units
rather than in huge_page_shift.

Johannes said:

: The resulting index may not be too big, but it can be too small: assume
: hpage size of 2M and the address to unmap to be 0x200000.  This is regular
: page index 512 and hpage index 1.  If you have a VMA that maps the file
: only starting at the second huge page, that VMAs vm_pgoff will be 512 but
: you ask for offset 1 and miss it even though it does map the page of
: interest.  hugetlb_cow() will try to unmap, miss the vma, and retry the
: cow until the allocation succeeds or the skipped vma(s) go away.

Signed-off-by: Michal Hocko <mhocko@...e.cz>
Acked-by: Hillf Danton <dhillf@...il.com>
Cc: Mel Gorman <mel@....ul.ie>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: David Rientjes <rientjes@...gle.com>
Acked-by: Johannes Weiner <hannes@...xchg.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 mm/hugetlb.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 8536741..de5d1dc 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2480,7 +2480,8 @@ static int unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma,
 	 * from page cache lookup which is in HPAGE_SIZE units.
 	 */
 	address = address & huge_page_mask(h);
-	pgoff = vma_hugecache_offset(h, vma, address);
+	pgoff = ((address - vma->vm_start) >> PAGE_SHIFT) +
+			vma->vm_pgoff;
 	mapping = vma->vm_file->f_dentry->d_inode->i_mapping;

 	/*

--
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