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Subject[ 32/54] hugetlb: prevent BUG_ON in hugetlb_fault() -> hugetlb_cow()
3.0-stable review patch.  If anyone has any objections, please let me know.


From: Chris Metcalf <>

commit 4998a6c0edce7fae9c0a5463f6ec3fa585258ee7 upstream.

Commit 66aebce747eaf ("hugetlb: fix race condition in hugetlb_fault()")
added code to avoid a race condition by elevating the page refcount in
hugetlb_fault() while calling hugetlb_cow().

However, one code path in hugetlb_cow() includes an assertion that the
page count is 1, whereas it may now also have the value 2 in this path.

The consensus is that this BUG_ON has served its purpose, so rather than
extending it to cover both cases, we just remove it.

Signed-off-by: Chris Metcalf <>
Acked-by: Mel Gorman <>
Acked-by: Hillf Danton <>
Acked-by: Hugh Dickins <>
Cc: Michal Hocko <>
Cc: KAMEZAWA Hiroyuki <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Greg Kroah-Hartman <>

mm/hugetlb.c | 1 -
1 file changed, 1 deletion(-)

--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2398,7 +2398,6 @@ retry_avoidcopy:
if (outside_reserve) {
if (unmap_ref_private(mm, vma, old_page, address)) {
- BUG_ON(page_count(old_page) != 1);
goto retry_avoidcopy;

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