Hi martin Thanks for your kindly response. On 03/02/2018 09:43 AM, Martin K. Petersen wrote: > > Jianchao, > >> 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. >> * 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: > > Please add something akin to Bart's explanation as a comment and repost. yes, sure. Thanks Jianchao
