scsi: convert host_busy to atomic_t

Avoid taking the host-wide host_lock to check the per-host 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, 3 insertions, 2 deletions

diff --git a/drivers/scsi/libsas/sas_scsi_host.c b/drivers/scsi/libsas/sas_scsi_host.c
index 7d02a19419a7..24e477d2ea70 100644
--- a/drivers/scsi/libsas/sas_scsi_host.c
+++ b/drivers/scsi/libsas/sas_scsi_host.c
@@ -813,7 +813,7 @@ retry:
         spin_unlock_irq(shost->host_lock);
 
         SAS_DPRINTK("Enter %s busy: %d failed: %d\n",
-                    __func__, shost->host_busy, shost->host_failed);
+                    __func__, atomic_read(&shost->host_busy), shost->host_failed);
         /*
          * Deal with commands that still have SAS tasks (i.e. they didn't
          * complete via the normal sas_task completion mechanism),
@@ -858,7 +858,8 @@ out:
                 goto retry;
 
         SAS_DPRINTK("--- Exit %s: busy: %d failed: %d tries: %d\n",
-                    __func__, shost->host_busy, shost->host_failed, tries);
+                    __func__, atomic_read(&shost->host_busy),
+                    shost->host_failed, tries);
 }
 
 enum blk_eh_timer_return sas_scsi_timed_out(struct scsi_cmnd *cmd)