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authorMinchan Kim <minchan.kim@gmail.com>2011-10-31 17:09:28 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-10-31 17:30:50 -0700
commit21ee9f398be209ccbb62929d35961ca1ed48eec3 (patch)
tree4127e14f4a07a2cb7bc6eb902e9c7b0baab8e84f /mm/vmscan.c
parent2f1da6421570d064a94e17190a4955c2df99794d (diff)
vmscan: add barrier to prevent evictable page in unevictable list
When a race between putback_lru_page() and shmem_lock with lock=0 happens, progrom execution order is as follows, but clear_bit in processor #1 could be reordered right before spin_unlock of processor #1. Then, the page would be stranded on the unevictable list. spin_lock SetPageLRU spin_unlock clear_bit(AS_UNEVICTABLE) spin_lock if PageLRU() if !test_bit(AS_UNEVICTABLE) move evictable list smp_mb if !test_bit(AS_UNEVICTABLE) move evictable list spin_unlock But, pagevec_lookup() in scan_mapping_unevictable_pages() has rcu_read_[un]lock() so it could protect reordering before reaching test_bit(AS_UNEVICTABLE) on processor #1 so this problem never happens. But it's a unexpected side effect and we should solve this problem properly. This patch adds a barrier after mapping_clear_unevictable. I didn't meet this problem but just found during review. Signed-off-by: Minchan Kim <minchan.kim@gmail.com> Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Rik van Riel <riel@redhat.com> Cc: Lee Schermerhorn <lee.schermerhorn@hp.com> Acked-by: Johannes Weiner <jweiner@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/vmscan.c')
-rw-r--r--mm/vmscan.c11
1 files changed, 6 insertions, 5 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3886b0bd786..f51a33e8ed8 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -633,13 +633,14 @@ redo:
lru = LRU_UNEVICTABLE;
add_page_to_unevictable_list(page);
/*
- * When racing with an mlock clearing (page is
- * unlocked), make sure that if the other thread does
- * not observe our setting of PG_lru and fails
- * isolation, we see PG_mlocked cleared below and move
+ * When racing with an mlock or AS_UNEVICTABLE clearing
+ * (page is unlocked) make sure that if the other thread
+ * does not observe our setting of PG_lru and fails
+ * isolation/check_move_unevictable_page,
+ * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
* the page back to the evictable list.
*
- * The other side is TestClearPageMlocked().
+ * The other side is TestClearPageMlocked() or shmem_lock().
*/
smp_mb();
}