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

commit 1f64d69c7ad2e48e697493e45590679f7a69b7b2 upstream.

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 8ee804bdbbab099b52bc8fb0f9476499fc986d26..2697806746d0530b32eadc900014bef205c4790a 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2668,7 +2668,8 @@ 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);