[PATCH] SCSI: don't hold device refcount in IO path

[Ming Lei <ming.lei@xxxxxxxxxx>]

scsi_device's refcount is always grabed in IO path.

Turns out it isn't necessary, becasue blk_queue_cleanup() will
drain any in-flight IOs, then cancel timeout/requeue work, and
SCSI's requeue_work is canceled too in __scsi_remove_device().

Also scsi_device won't go away until blk_cleanup_queue() is done.

So don't hold the refcount in IO path.

Cc: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
Cc: James Smart <james.smart@xxxxxxxxxxxx>
Cc: Bart Van Assche <bart.vanassche@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>,
Cc: jianchao wang <jianchao.w.wang@xxxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
 drivers/scsi/scsi_lib.c | 17 ++---------------
 1 file changed, 2 insertions(+), 15 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 601b9f1de267..a095426b1c7a 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -141,8 +141,6 @@ scsi_set_blocked(struct scsi_cmnd *cmd, int reason)
 
 static void scsi_mq_requeue_cmd(struct scsi_cmnd *cmd)
 {
-	struct scsi_device *sdev = cmd->device;
-
 	if (cmd->request->rq_flags & RQF_DONTPREP) {
 		cmd->request->rq_flags &= ~RQF_DONTPREP;
 		scsi_mq_uninit_cmd(cmd);
@@ -150,7 +148,6 @@ static void scsi_mq_requeue_cmd(struct scsi_cmnd *cmd)
 		WARN_ON_ONCE(true);
 	}
 	blk_mq_requeue_request(cmd->request, true);
-	put_device(&sdev->sdev_gendev);
 }
 
 /**
@@ -201,7 +198,6 @@ static void __scsi_queue_insert(struct scsi_cmnd *cmd, int reason, bool unbusy)
 	 * happened.
 	 */
 	blk_mq_requeue_request(cmd->request, true);
-	put_device(&device->sdev_gendev);
 }
 
 /*
@@ -619,7 +615,6 @@ static bool scsi_end_request(struct request *req, blk_status_t error,
 		blk_mq_run_hw_queues(q, true);
 
 	percpu_ref_put(&q->q_usage_counter);
-	put_device(&sdev->sdev_gendev);
 	return false;
 }
 
@@ -1613,7 +1608,6 @@ static void scsi_mq_put_budget(struct blk_mq_hw_ctx *hctx)
 	struct scsi_device *sdev = q->queuedata;
 
 	atomic_dec(&sdev->device_busy);
-	put_device(&sdev->sdev_gendev);
 }
 
 static bool scsi_mq_get_budget(struct blk_mq_hw_ctx *hctx)
@@ -1621,16 +1615,9 @@ static bool scsi_mq_get_budget(struct blk_mq_hw_ctx *hctx)
 	struct request_queue *q = hctx->queue;
 	struct scsi_device *sdev = q->queuedata;
 
-	if (!get_device(&sdev->sdev_gendev))
-		goto out;
-	if (!scsi_dev_queue_ready(q, sdev))
-		goto out_put_device;
-
-	return true;
+	if (scsi_dev_queue_ready(q, sdev))
+		return true;
 
-out_put_device:
-	put_device(&sdev->sdev_gendev);
-out:
 	if (atomic_read(&sdev->device_busy) == 0 && !scsi_device_blocked(sdev))
 		blk_mq_delay_run_hw_queue(hctx, SCSI_QUEUE_DELAY);
 	return false;
-- 
2.9.5