scsi: core: don't hold device refcount in IO path

scsi_device's refcount is always grabbed in IO path.

Turns out it isn't necessary, because 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, especially the refcount isn't
required in IO path since blk_queue_enter() / blk_queue_exit() is
introduced in the legacy block layer.

Cc: Dongli Zhang <dongli.zhang@oracle.com>
Cc: James Smart <james.smart@broadcom.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Cc: linux-scsi@vger.kernel.org,
Cc: Martin K . Petersen <martin.petersen@oracle.com>,
Cc: Christoph Hellwig <hch@lst.de>,
Cc: James E . J . Bottomley <jejb@linux.vnet.ibm.com>,
Cc: jianchao wang <jianchao.w.wang@oracle.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index d4bd6cd9d373289cfbd8a0fe4eff199c7431ee05..6b2570a5642da55712a0aa821526a5868c926338 100644 (file)
--- 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);
 }
 
 /**
@@ -189,19 +186,7 @@ static void __scsi_queue_insert(struct scsi_cmnd *cmd, int reason, bool unbusy)
         */
        cmd->result = 0;
 
-       /*
-        * Before a SCSI command is dispatched,
-        * get_device(&sdev->sdev_gendev) is called and the host,
-        * target and device busy counters are increased. Since
-        * requeuing a request causes these actions to be repeated and
-        * since scsi_device_unbusy() has already been called,
-        * put_device(&device->sdev_gendev) must still be called. Call
-        * put_device() after blk_mq_requeue_request() to avoid that
-        * removal of the SCSI device can start before requeueing has
-        * happened.
-        */
        blk_mq_requeue_request(cmd->request, true);
-       put_device(&device->sdev_gendev);
 }
 
 /*
@@ -619,7 +604,6 @@ 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 +1597,6 @@ 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 +1604,9 @@ 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;