scsi: convert target_busy to an atomic_t

Avoid taking the host-wide host_lock to check the per-target queue limit.
Instead we do an atomic_inc_return early on to grab our slot in the queue,
and if necessary decrement it after finishing all checks.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Webb Scales <webbnh@hp.com>
Acked-by: Jens Axboe <axboe@kernel.dk>
Tested-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Robert Elliott <elliott@hp.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 9aa38f7b303b..4e078b63a9e5 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -291,8 +291,8 @@ struct scsi_target {
         unsigned int            expecting_lun_change:1; /* A device has reported
                                                  * a 3F/0E UA, other devices on
                                                  * the same target will also. */
-        /* commands actually active on LLD. protected by host lock. */
-        unsigned int            target_busy;
+        /* commands actually active on LLD. */
+        atomic_t                target_busy;
         /*
          * LLDs should set this in the slave_alloc host template callout.
          * If set to zero then there is not limit.