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authorLinus Torvalds <torvalds@g5.osdl.org>2005-10-16 17:36:06 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2005-10-16 17:36:06 -0700
commit3d80636a0d5f056ffc26472d05b6027a7a9f6e1c (patch)
tree39b3dbae53938728c55b2312190561b858431d92
parent688ce17b8599abc548b406c00e4d18ae0dec954f (diff)
downloadop-kernel-dev-3d80636a0d5f056ffc26472d05b6027a7a9f6e1c.zip
op-kernel-dev-3d80636a0d5f056ffc26472d05b6027a7a9f6e1c.tar.gz
Fix memory ordering bug in page reclaim
As noticed by Nick Piggin, we need to make sure that we check the page count before we check for PageDirty, since the dirty check is only valid if the count implies that we're the only possible ones holding the page. We always did do this, but the code needs a read-memory-barrier to make sure that the orderign is also honored by the CPU. (The writer side is ordered due to the atomic decrement and test on the page count, see the discussion on linux-kernel) Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--mm/vmscan.c13
1 files changed, 9 insertions, 4 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0ea71e8..64f9570 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -511,10 +511,11 @@ static int shrink_list(struct list_head *page_list, struct scan_control *sc)
* PageDirty _after_ making sure that the page is freeable and
* not in use by anybody. (pagecache + us == 2)
*/
- if (page_count(page) != 2 || PageDirty(page)) {
- write_unlock_irq(&mapping->tree_lock);
- goto keep_locked;
- }
+ if (unlikely(page_count(page) != 2))
+ goto cannot_free;
+ smp_rmb();
+ if (unlikely(PageDirty(page)))
+ goto cannot_free;
#ifdef CONFIG_SWAP
if (PageSwapCache(page)) {
@@ -538,6 +539,10 @@ free_it:
__pagevec_release_nonlru(&freed_pvec);
continue;
+cannot_free:
+ write_unlock_irq(&mapping->tree_lock);
+ goto keep_locked;
+
activate_locked:
SetPageActive(page);
pgactivate++;
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