On Fri, 2018-04-20 at 14:57 +0800, Ming Lei wrote:
> +struct scsi_host_mq_in_flight {
> + int cnt;
> +};
> +
> +static void scsi_host_check_in_flight(struct request *rq, void *data,
> + bool reserved)
> +{
> + struct scsi_host_mq_in_flight *in_flight = data;
> +
> + if (blk_mq_request_started(rq))
> + in_flight->cnt++;
> +}
> +
> /**
> * scsi_host_busy - Return the host busy counter
> * @shost: Pointer to Scsi_Host to inc.
> **/
> int scsi_host_busy(struct Scsi_Host *shost)
> {
> - return atomic_read(&shost->host_busy);
> + struct scsi_host_mq_in_flight in_flight = {
> + .cnt = 0,
> + };
> +
> + if (!shost->use_blk_mq)
> + return atomic_read(&shost->host_busy);
> +
> + blk_mq_tagset_busy_iter(&shost->tag_set, scsi_host_check_in_flight,
> + &in_flight);
> + return in_flight.cnt;
> }
> EXPORT_SYMBOL(scsi_host_busy);
This patch introduces a subtle behavior change that has not been explained
in the commit message. If a SCSI request gets requeued that results in a
decrease of the .host_busy counter by scsi_device_unbusy() before the request
is requeued and an increase of the host_busy counter when scsi_queue_rq() is
called again. During that time such requests have the state MQ_RQ_COMPLETE and
hence blk_mq_request_started() will return true and scsi_host_check_in_flight()
will include these requests. In other words, this patch introduces a subtle
behavior change that has not been explained in the commit message. Hence I'm
doubt that this change is correct.
Bart.
