From: Naoya Horiguchi <>

3.4.113-rc1 review patch.  If anyone has any objections, please let me know.


commit 0d777df5d8953293be090d9ab5a355db893e8357 upstream.

Currently at the beginning of hugetlb_fault(), we call huge_pte_offset()
and check whether the obtained *ptep is a migration/hwpoison entry or
not.  And if not, then we get to call huge_pte_alloc().  This is racy
because the *ptep could turn into migration/hwpoison entry after the
huge_pte_offset() check.  This race results in BUG_ON in

We don't have to call huge_pte_alloc() when the huge_pte_offset()
returns non-NULL, so let's fix this bug with moving the code into else

Note that the *ptep could turn into a migration/hwpoison entry after
this block, but that's not a problem because we have another
!pte_present check later (we never go into hugetlb_no_page() in that

Fixes: 290408d4a250 ("hugetlb: hugepage migration core")
Signed-off-by: Naoya Horiguchi <>
Acked-by: Hillf Danton <>
Acked-by: David Rientjes <>
Cc: Hugh Dickins <>
Cc: Dave Hansen <>
Cc: Mel Gorman <>
Cc: Joonsoo Kim <>
Cc: Mike Kravetz <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
[lizf: Backported to 3.4: adjust context]
Signed-off-by: Zefan Li <>
 mm/hugetlb.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index e622aab..416cbfd 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2835,12 +2835,12 @@ int hugetlb_fault(struct mm_struct *mm, struct 
vm_area_struct *vma,
                } else if (unlikely(is_hugetlb_entry_hwpoisoned(entry)))
                        return VM_FAULT_HWPOISON_LARGE |
                               VM_FAULT_SET_HINDEX(h - hstates);
+       } else {
+               ptep = huge_pte_alloc(mm, address, huge_page_size(h));
+               if (!ptep)
+                       return VM_FAULT_OOM;
-       ptep = huge_pte_alloc(mm, address, huge_page_size(h));
-       if (!ptep)
-               return VM_FAULT_OOM;
         * Serialize hugepage allocation and instantiation, so that we don't
         * get spurious allocation failures if two CPUs race to instantiate

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