The function xfs_buftarg_isolate() used by xfs buffer schrinkers
to determine whether a buffer should be isolated and disposed
from LRU list, has inverted logic.
Excerpt from xfs_buftarg_isolate():
/*
* Decrement the b_lru_ref count unless the value is already
* zero. If the value is already zero, we need to reclaim the
* buffer, otherwise it gets another trip through the LRU.
*/
if (!atomic_add_unless(&bp->b_lru_ref, -1, 0)) {
spin_unlock(&bp->b_lock);
return LRU_ROTATE;
}
However, as per documentation, atomic_add_unless() returns _zero_
if the atomic value was originally equal to the specified *unsless* value.
Ultimately causing a xfs_buffer with ->b_lru_ref == 0, to take another
trip around LRU, while isolating buffers with non-zero b_lru_ref.
Signed-off-by: Vratislav Bendel <vbendel@xxxxxxxxxx>
CC: Brian Foster <bfoster@xxxxxxxxxx>
---
fs/xfs/xfs_buf.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index d1da2ee9e6db..ac669a10c62f 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -1708,7 +1708,7 @@ xfs_buftarg_isolate(
* zero. If the value is already zero, we need to reclaim the
* buffer, otherwise it gets another trip through the LRU.
*/
- if (!atomic_add_unless(&bp->b_lru_ref, -1, 0)) {
+ if (atomic_add_unless(&bp->b_lru_ref, -1, 0)) {
spin_unlock(&bp->b_lock);
return LRU_ROTATE;
}
--
2.14.3
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