xfs: avoid taking the ilock unnessecarily in xfs_qm_dqattach
Check if we actually need to attach a dquot before taking the ilock in xfs_qm_dqattach. This avoid superflous lock roundtrips for the common cases of quota support compiled in but not activated on a filesystem and an inode that already has the dquots attached. Signed-off-by: NChristoph Hellwig <hch@lst.de> Reviewed-by: NMark Tinguely <tinguely@sgi.com> Reviewed-by: NDave Chinner <dchinner@redhat.com> Signed-off-by: NBen Myers <bpm@sgi.com>
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