From: Ming Lei ming.lei@redhat.com
commit 826a70a08b1210bbfdbda812ab43eb986e25b5c2 upstream
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: 0df21c86bdbf(scsi: implement .get_budget and .put_budget for blk-mq) Reported-by: Bart Van Assche bart.vanassche@wdc.com Signed-off-by: Ming Lei ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk [jwang: fix conflict in scsi_lib.c] Signed-off-by: Jack Wang jinpu.wang@profitbricks.com --- drivers/scsi/scsi_lib.c | 29 +++++++++++++---------------- 1 file changed, 13 insertions(+), 16 deletions(-)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index c3f9d6d7a724..51265d2cfbb4 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -1974,11 +1974,7 @@ 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;
- scsi_dec_host_busy(shost); - if (scsi_target(sdev)->can_queue > 0) - atomic_dec(&scsi_target(sdev)->target_busy); atomic_dec(&sdev->device_busy); put_device(&sdev->sdev_gendev); } @@ -1987,7 +1983,6 @@ 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)); @@ -1998,18 +1993,9 @@ 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: @@ -2022,6 +2008,7 @@ 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; @@ -2031,10 +2018,15 @@ 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); @@ -2052,11 +2044,16 @@ 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: + scsi_dec_host_busy(shost); +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) {