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[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>
This commit is contained in:
Nick Piggin 2006-02-07 12:58:52 -08:00 committed by Linus Torvalds
parent 99f6d61bda
commit 8519fb30e4
2 changed files with 24 additions and 12 deletions
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2
include/linux/mm.h
View File

@ -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); \
})

34
mm/swap.c
View File

@ -34,19 +34,22 @@
/* How many pages do we try to swap or page in/out together? */
int page_cluster;
static void put_compound_page(struct page *page)
{
page = (struct page *)page_private(page);
if (put_page_testzero(page)) {
void (*dtor)(struct page *page);
dtor = (void (*)(struct page *))page[1].mapping;
(*dtor)(page);
}
}
void put_page(struct page *page)
{
if (unlikely(PageCompound(page))) {
page = (struct page *)page_private(page);
if (put_page_testzero(page)) {
void (*dtor)(struct page *page);
dtor = (void (*)(struct page *))page[1].mapping;
(*dtor)(page);
}
return;
}
if (put_page_testzero(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;