On Thu, 2019-04-04 at 16:43 +0800, Ming Lei wrote:
> 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.zh...@oracle.com>
> Cc: James Smart <james.sm...@broadcom.com>
> Cc: Bart Van Assche <bart.vanass...@wdc.com>
> Cc: linux-scsi@vger.kernel.org,
> Cc: Martin K . Petersen <martin.peter...@oracle.com>,
> Cc: Christoph Hellwig <h...@lst.de>,
> Cc: James E . J . Bottomley <j...@linux.vnet.ibm.com>,
> Cc: jianchao wang <jianchao.w.w...@oracle.com>
> Signed-off-by: Ming Lei <ming....@redhat.com>
> ---
> drivers/scsi/scsi_lib.c | 28 ++--------------------------
> 1 file changed, 2 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 601b9f1de267..3369d66911eb 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);
> }
>
> /**
> @@ -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;
Reviewed-by: Bart Van Assche <bvanass...@acm.org>
