Commit 8519fb30 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
Browse files

[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: default avatarNick Piggin <npiggin@suse.de>
Acked-by: default avatarHugh Dickins <hugh@veritas.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 99f6d61b

include/linux/mm.h

+1 −1
Original line number Diff line number Diff line
@@ -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);	\

	})

mm/swap.c

+22 −10
Original line number Diff line number Diff line
@@ -34,9 +34,8 @@ 
/* How many pages do we try to swap or page in/out together? */

int page_cluster;



void put_page(struct page *page)

static void put_compound_page(struct page *page)

{

	if (unlikely(PageCompound(page))) {

	page = (struct page *)page_private(page);

	if (put_page_testzero(page)) {

		void (*dtor)(struct page *page);
@@ -44,9 +43,13 @@ void put_page(struct page *page) 
		dtor = (void (*)(struct page *))page[1].mapping;

		(*dtor)(page);

	}

		return;

}

	if (put_page_testzero(page))



void put_page(struct page *page)

{

	if (unlikely(PageCompound(page)))

		put_compound_page(page);

	else if (put_page_testzero(page))

		__page_cache_release(page);

}

EXPORT_SYMBOL(put_page);
@@ -244,6 +247,15 @@ void release_pages(struct page **pages, int nr, int cold) 
		struct page *page = pages[i];

		struct zone *pagezone;



		if (unlikely(PageCompound(page))) {

			if (zone) {

				spin_unlock_irq(&zone->lru_lock);

				zone = NULL;

			}

			put_compound_page(page);

			continue;

		}



		if (!put_page_testzero(page))

			continue;

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