hugetlb: add missing unlock in avoidcopy path in hugetlb_cow()

This patch fixes possible deadlock in hugepage lock_page()
by adding missing unlock_page().

libhugetlbfs test will hit this bug when the next patch in this
patchset ("hugetlb, HWPOISON: move PG_HWPoison bit check") is applied.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Acked-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 3c275ffd32a..303fb0c0236 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2324,9 +2324,11 @@ retry_avoidcopy:
          * and just make the page writable */
         avoidcopy = (page_mapcount(old_page) == 1);
         if (avoidcopy) {
-                if (!trylock_page(old_page))
+                if (!trylock_page(old_page)) {
                         if (PageAnon(old_page))
                                 page_move_anon_rmap(old_page, vma, address);
+                } else
+                        unlock_page(old_page);
                 set_huge_ptep_writable(vma, address, ptep);
                 return 0;
         }