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Commit 826a70a0 authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

SCSI: don't get target/host busy_count in scsi_mq_get_budget() 



It is very expensive to atomic_inc/atomic_dec the host wide counter of
host->busy_count, and it should have been avoided via blk-mq's mechanism
of getting driver tag, which uses the more efficient way of sbitmap queue.

Also we don't check atomic_read(&sdev->device_busy) in scsi_mq_get_budget()
and don't run queue if the counter becomes zero, so IO hang may be caused
if all requests are completed just before the current SCSI device
is added to shost->starved_list.

Fixes: 0df21c86(scsi: implement .get_budget and .put_budget for blk-mq)
Reported-by: default avatarBart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent e4f36b24

drivers/scsi/scsi_lib.c

+13 −16
Original line number Diff line number Diff line
@@ -1950,11 +1950,7 @@ static void scsi_mq_put_budget(struct blk_mq_hw_ctx *hctx) 
{

	struct request_queue *q = hctx->queue;

	struct scsi_device *sdev = q->queuedata;

	struct Scsi_Host *shost = sdev->host;



	atomic_dec(&shost->host_busy);

	if (scsi_target(sdev)->can_queue > 0)

		atomic_dec(&scsi_target(sdev)->target_busy);

	atomic_dec(&sdev->device_busy);

	put_device(&sdev->sdev_gendev);

}
@@ -1963,7 +1959,6 @@ static blk_status_t scsi_mq_get_budget(struct blk_mq_hw_ctx *hctx) 
{

	struct request_queue *q = hctx->queue;

	struct scsi_device *sdev = q->queuedata;

	struct Scsi_Host *shost = sdev->host;

	blk_status_t ret;



	ret = prep_to_mq(scsi_prep_state_check(sdev, NULL));
@@ -1974,18 +1969,9 @@ static blk_status_t scsi_mq_get_budget(struct blk_mq_hw_ctx *hctx) 
		goto out;

	if (!scsi_dev_queue_ready(q, sdev))

		goto out_put_device;

	if (!scsi_target_queue_ready(shost, sdev))

		goto out_dec_device_busy;

	if (!scsi_host_queue_ready(q, shost, sdev))

		goto out_dec_target_busy;



	return BLK_STS_OK;



out_dec_target_busy:

	if (scsi_target(sdev)->can_queue > 0)

		atomic_dec(&scsi_target(sdev)->target_busy);

out_dec_device_busy:

	atomic_dec(&sdev->device_busy);

out_put_device:

	put_device(&sdev->sdev_gendev);

out:
@@ -1998,6 +1984,7 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx, 
	struct request *req = bd->rq;

	struct request_queue *q = req->q;

	struct scsi_device *sdev = q->queuedata;

	struct Scsi_Host *shost = sdev->host;

	struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req);

	blk_status_t ret;

	int reason;
@@ -2007,10 +1994,15 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx, 
		goto out_put_budget;



	ret = BLK_STS_RESOURCE;

	if (!scsi_target_queue_ready(shost, sdev))

		goto out_put_budget;

	if (!scsi_host_queue_ready(q, shost, sdev))

		goto out_dec_target_busy;



	if (!(req->rq_flags & RQF_DONTPREP)) {

		ret = prep_to_mq(scsi_mq_prep_fn(req));

		if (ret != BLK_STS_OK)

			goto out_put_budget;

			goto out_dec_host_busy;

		req->rq_flags |= RQF_DONTPREP;

	} else {

		blk_mq_start_request(req);
@@ -2028,11 +2020,16 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx, 
	if (reason) {

		scsi_set_blocked(cmd, reason);

		ret = BLK_STS_RESOURCE;

		goto out_put_budget;

		goto out_dec_host_busy;

	}



	return BLK_STS_OK;



out_dec_host_busy:

       atomic_dec(&shost->host_busy);

out_dec_target_busy:

	if (scsi_target(sdev)->can_queue > 0)

		atomic_dec(&scsi_target(sdev)->target_busy);

out_put_budget:

	scsi_mq_put_budget(hctx);

	switch (ret) {