Messages in this thread Patch in this message | | | From | Vratislav Bendel <> | Subject | [PATCH] xfs: Correctly invert xfs_buftarg LRU isolation logic | Date | Wed, 28 Feb 2018 16:49:51 +0100 |
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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@redhat.com> CC: Brian Foster <bfoster@redhat.com> --- 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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