Hi Bart Thanks for your precious time and detailed summary. On 03/02/2018 01:43 AM, Bart Van Assche wrote: > Yes, the block layer core guarantees that scsi_mq_get_budget() will be called > before scsi_queue_rq(). I think the full picture is as follows: > * Before scsi_queue_rq() calls .queuecommand(), get_device() is called for the > SCSI device and the device, target and host busy counters are incremented. Supply some details here: scsi_mq_get_budget before calling .queuecommand get_device and increase device_busy. scsi_queue_rq increases target_busy and host_busy. > * If the SCSI core decides to requeue a command, scsi_queue_insert() causes > __scsi_queue_insert() to call scsi_device_unbusy(). That last function > decreases the device, target and host busy counters but not put_device(sdev). > Hence the need for a separate put_device() call after requeuing. > > It's unfortunate that the SCSI core became so asymmetric. Anyway, since I am > now convinced that this patch is correct, feel free to add: > > Reviewed-by: Bart Van Assche <bart.vanassche@xxxxxxx> Sincerely Jianchao
