linux-kernel - [PATCH 3.11 56/66] mm: fix BUG in __split_huge_page

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Date:	Fri,  1 Nov 2013 15:07:32 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 3.11 56/66] mm: fix BUG in __split_huge_page_pmd

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

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

From: Hugh Dickins <hughd@...gle.com>

commit 750e8165f5e87b6a142be953640eabb13a9d350a upstream.

Occasionally we hit the BUG_ON(pmd_trans_huge(*pmd)) at the end of
__split_huge_page_pmd(): seen when doing madvise(,,MADV_DONTNEED).

It's invalid: we don't always have down_write of mmap_sem there: a racing
do_huge_pmd_wp_page() might have copied-on-write to another huge page
before our split_huge_page() got the anon_vma lock.

Forget the BUG_ON, just go back and try again if this happens.

Signed-off-by: Hugh Dickins <hughd@...gle.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc: David Rientjes <rientjes@...gle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/huge_memory.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2709,6 +2709,7 @@ void __split_huge_page_pmd(struct vm_are

 	mmun_start = haddr;
 	mmun_end   = haddr + HPAGE_PMD_SIZE;
+again:
 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
 	spin_lock(&mm->page_table_lock);
 	if (unlikely(!pmd_trans_huge(*pmd))) {
@@ -2731,7 +2732,14 @@ void __split_huge_page_pmd(struct vm_are
 	split_huge_page(page);

 	put_page(page);
-	BUG_ON(pmd_trans_huge(*pmd));
+
+	/*
+	 * We don't always have down_write of mmap_sem here: a racing
+	 * do_huge_pmd_wp_page() might have copied-on-write to another
+	 * huge page before our split_huge_page() got the anon_vma lock.
+	 */
+	if (unlikely(pmd_trans_huge(*pmd)))
+		goto again;
 }

 void split_huge_page_pmd_mm(struct mm_struct *mm, unsigned long address,

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