+ mm-hugetlb-call-huge_pte_alloc-only-if-ptep-is-null.patch added to -mm tree

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The patch titled
     Subject: mm: hugetlb: call huge_pte_alloc() only if ptep is null
has been added to the -mm tree.  Its filename is
     mm-hugetlb-call-huge_pte_alloc-only-if-ptep-is-null.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/mm-hugetlb-call-huge_pte_alloc-only-if-ptep-is-null.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/mm-hugetlb-call-huge_pte_alloc-only-if-ptep-is-null.patch

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------------------------------------------------------
From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Subject: mm: hugetlb: call huge_pte_alloc() only if ptep is null

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 huge_pte_alloc().

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 block.

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 case.)

Fixes: 290408d4a250 ("hugetlb: hugepage migration core")
Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>	[2.6.36+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/hugetlb.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff -puN mm/hugetlb.c~mm-hugetlb-call-huge_pte_alloc-only-if-ptep-is-null mm/hugetlb.c
--- a/mm/hugetlb.c~mm-hugetlb-call-huge_pte_alloc-only-if-ptep-is-null
+++ a/mm/hugetlb.c
@@ -3696,12 +3696,12 @@ int hugetlb_fault(struct mm_struct *mm,
 		} else if (unlikely(is_hugetlb_entry_hwpoisoned(entry)))
 			return VM_FAULT_HWPOISON_LARGE |
 				VM_FAULT_SET_HINDEX(hstate_index(h));
+	} 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;
-
 	mapping = vma->vm_file->f_mapping;
 	idx = vma_hugecache_offset(h, vma, address);
 
_

Patches currently in -mm which might be from n-horiguchi@xxxxxxxxxxxxx are

mm-hugetlb-fix-hugepage-memory-leak-caused-by-wrong-reserve-count.patch
mm-hugetlb-call-huge_pte_alloc-only-if-ptep-is-null.patch
rmap-add-argument-to-charge-compound-page-fix.patch
mm-hwpoison-adjust-for-new-thp-refcounting.patch

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