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author | Minchan Kim <minchan.kim@gmail.com> | 2011-10-31 17:09:28 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2011-10-31 17:30:50 -0700 |
commit | 21ee9f398be209ccbb62929d35961ca1ed48eec3 (patch) | |
tree | 4127e14f4a07a2cb7bc6eb902e9c7b0baab8e84f /mm/shmem.c | |
parent | 2f1da6421570d064a94e17190a4955c2df99794d (diff) | |
download | linux-21ee9f398be209ccbb62929d35961ca1ed48eec3.tar.gz linux-21ee9f398be209ccbb62929d35961ca1ed48eec3.tar.bz2 linux-21ee9f398be209ccbb62929d35961ca1ed48eec3.zip |
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/shmem.c')
-rw-r--r-- | mm/shmem.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/mm/shmem.c b/mm/shmem.c index 2d3577295298..fa4fa6ce13bc 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1068,6 +1068,12 @@ int shmem_lock(struct file *file, int lock, struct user_struct *user) user_shm_unlock(inode->i_size, user); info->flags &= ~VM_LOCKED; mapping_clear_unevictable(file->f_mapping); + /* + * Ensure that a racing putback_lru_page() can see + * the pages of this mapping are evictable when we + * skip them due to !PageLRU during the scan. + */ + smp_mb__after_clear_bit(); scan_mapping_unevictable_pages(file->f_mapping); } retval = 0; |