[PATCH] mm: compound release fix

Compound pages on SMP systems can now often be freed from pagetables via
the release_pages path.  This uses put_page_testzero which does not handle
compound pages at all.  Releasing constituent pages from process mappings
decrements their count to a large negative number and leaks the reference
at the head page - net result is a memory leak.

The problem was hidden because the debug check in put_page_testzero itself
actually did take compound pages into consideration.

Fix the bug and the debug check.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Acked-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 85854b867463..75e9f0724997 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -303,7 +303,7 @@ struct page {
  */
 #define put_page_testzero(p)                            \
         ({                                              \
-                BUG_ON(page_count(p) == 0);             \
+                BUG_ON(atomic_read(&(p)->_count) == -1);\
                 atomic_add_negative(-1, &(p)->_count);  \
         })