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Commit 18c4f0a4 authored by Ming Lei's avatar Ming Lei Committed by Martin K. Petersen
Browse files

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: default avatarBart Van Assche <bvanassche@acm.org>
Reviewed-by: default avatarHannes Reinecke <hare@suse.com>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarMartin K. Petersen <martin.petersen@oracle.com>
parent 1710ac17

drivers/scsi/scsi_lib.c

+2 −26
Original line number Diff line number Diff line
@@ -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;



	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;