From 8519fb30e438f8088b71a94a7d5a660a814d3872 Mon Sep 17 00:00:00 2001
From: Nick Piggin <npiggin@suse.de>
Date: Tue, 7 Feb 2006 12:58:52 -0800
Subject: [PATCH] [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>
---
include/linux/mm.h | 2 +-
mm/swap.c | 32 ++++++++++++++++++++++----------
2 files changed, 23 insertions(+), 11 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 85854b8674634..75e9f0724997e 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); \
})
diff --git a/mm/swap.c b/mm/swap.c
index bc2442a7b0eef..76247424dea18 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -34,19 +34,22 @@
/* 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);
+ 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;
+ dtor = (void (*)(struct page *))page[1].mapping;
+ (*dtor)(page);
}
- 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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