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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: 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>
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parent
e4f36b249b
commit
826a70a08b
1 changed files with 13 additions and 16 deletions
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@ -1950,11 +1950,7 @@ static void scsi_mq_put_budget(struct blk_mq_hw_ctx *hctx)
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{
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struct request_queue *q = hctx->queue;
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struct scsi_device *sdev = q->queuedata;
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struct Scsi_Host *shost = sdev->host;
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atomic_dec(&shost->host_busy);
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if (scsi_target(sdev)->can_queue > 0)
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atomic_dec(&scsi_target(sdev)->target_busy);
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atomic_dec(&sdev->device_busy);
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put_device(&sdev->sdev_gendev);
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}
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@ -1963,7 +1959,6 @@ static blk_status_t scsi_mq_get_budget(struct blk_mq_hw_ctx *hctx)
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{
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struct request_queue *q = hctx->queue;
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struct scsi_device *sdev = q->queuedata;
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struct Scsi_Host *shost = sdev->host;
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blk_status_t ret;
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ret = prep_to_mq(scsi_prep_state_check(sdev, NULL));
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@ -1974,18 +1969,9 @@ static blk_status_t scsi_mq_get_budget(struct blk_mq_hw_ctx *hctx)
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goto out;
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if (!scsi_dev_queue_ready(q, sdev))
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goto out_put_device;
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if (!scsi_target_queue_ready(shost, sdev))
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goto out_dec_device_busy;
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if (!scsi_host_queue_ready(q, shost, sdev))
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goto out_dec_target_busy;
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return BLK_STS_OK;
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out_dec_target_busy:
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if (scsi_target(sdev)->can_queue > 0)
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atomic_dec(&scsi_target(sdev)->target_busy);
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out_dec_device_busy:
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atomic_dec(&sdev->device_busy);
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out_put_device:
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put_device(&sdev->sdev_gendev);
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out:
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@ -1998,6 +1984,7 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
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struct request *req = bd->rq;
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struct request_queue *q = req->q;
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struct scsi_device *sdev = q->queuedata;
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struct Scsi_Host *shost = sdev->host;
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struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req);
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blk_status_t ret;
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int reason;
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@ -2007,10 +1994,15 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
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goto out_put_budget;
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ret = BLK_STS_RESOURCE;
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if (!scsi_target_queue_ready(shost, sdev))
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goto out_put_budget;
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if (!scsi_host_queue_ready(q, shost, sdev))
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goto out_dec_target_busy;
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if (!(req->rq_flags & RQF_DONTPREP)) {
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ret = prep_to_mq(scsi_mq_prep_fn(req));
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if (ret != BLK_STS_OK)
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goto out_put_budget;
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goto out_dec_host_busy;
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req->rq_flags |= RQF_DONTPREP;
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} else {
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blk_mq_start_request(req);
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@ -2028,11 +2020,16 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
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if (reason) {
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scsi_set_blocked(cmd, reason);
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ret = BLK_STS_RESOURCE;
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goto out_put_budget;
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goto out_dec_host_busy;
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}
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return BLK_STS_OK;
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out_dec_host_busy:
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atomic_dec(&shost->host_busy);
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out_dec_target_busy:
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if (scsi_target(sdev)->can_queue > 0)
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atomic_dec(&scsi_target(sdev)->target_busy);
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out_put_budget:
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scsi_mq_put_budget(hctx);
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switch (ret) {
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