mm/hugetlb.c: avoid double unlock_page() in hugetlb_fault()

Have hugetlb_fault() call unlock_page(page) only if it had previously
called lock_page(page).

Setting CONFIG_DEBUG_VM=y and then running the libhugetlbfs test suite,
resulted in the tripping of VM_BUG_ON(!PageLocked(page)) in
unlock_page() having been called by hugetlb_fault() when page ==
pagecache_page.  This patch remedied the problem.

Signed-off-by: Dean Nelson <dnelson@redhat.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index c4a3558589ab..85855240933d 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2738,7 +2738,8 @@ out_page_table_lock:
                 unlock_page(pagecache_page);
                 put_page(pagecache_page);
         }
-        unlock_page(page);
+        if (page != pagecache_page)
+                unlock_page(page);
 
 out_mutex:
         mutex_unlock(&hugetlb_instantiation_mutex);