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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Vratislav Bendel <vbendel@redhat.com>,
        Brian Foster <bfoster@redhat.com>,
        Christoph Hellwig <hch@lst.de>,
        "Darrick J. Wong" <darrick.wong@oracle.com>,
        Alex Lyakas <alex@zadara.com>
Subject: [PATCH 4.9 58/62] xfs: Correctly invert xfs_buftarg LRU isolation logic
Date:   Mon,  4 Nov 2019 22:45:20 +0100
Message-Id: <20191104211959.290977993@linuxfoundation.org>
In-Reply-To: <20191104211901.387893698@linuxfoundation.org>
References: <20191104211901.387893698@linuxfoundation.org>
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From: Vratislav Bendel <vbendel@redhat.com>

commit 19957a181608d25c8f4136652d0ea00b3738972d upstream.

Due to an inverted logic mistake in xfs_buftarg_isolate()
the xfs_buffers with zero b_lru_ref will take another trip
around LRU, while isolating buffers with non-zero b_lru_ref.

Additionally those isolated buffers end up right back on the LRU
once they are released, because b_lru_ref remains elevated.

Fix that circuitous route by leaving them on the LRU
as originally intended.

Signed-off-by: Vratislav Bendel <vbendel@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Alex Lyakas <alex@zadara.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/xfs/xfs_buf.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -1674,7 +1674,7 @@ 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;
 	}