Commits
Dave Chinner committed 1bfd8d04190
xfs: introduce inode cluster buffer trylocks for xfs_iflush There is an ABBA deadlock between synchronous inode flushing in xfs_reclaim_inode and xfs_icluster_free. xfs_icluster_free locks the buffer, then takes inode ilocks, whilst synchronous reclaim takes the ilock followed by the buffer lock in xfs_iflush(). To avoid this deadlock, separate the inode cluster buffer locking semantics from the synchronous inode flush semantics, allowing callers to attempt to lock the buffer but still issue synchronous IO if it can get the buffer. This requires xfs_iflush() calls that currently use non-blocking semantics to pass SYNC_TRYLOCK rather than 0 as the flags parameter. This allows xfs_reclaim_inode to avoid the deadlock on the buffer lock and detect the failure so that it can drop the inode ilock and restart the reclaim attempt on the inode. This allows xfs_ifree_cluster to obtain the inode lock, mark the inode stale and release it and hence defuse the deadlock situation. It also has the pleasant side effect of avoiding IO in xfs_reclaim_inode when it tries to next reclaim the inode as it is now marked stale. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Alex Elder <aelder@sgi.com>