On 2020-08-29 11:56, Alan Stern wrote: > A third possibility is the approach I outlined before, adding a > BLK_MQ_REQ_PM flag. But to avoid the deadlock you pointed out, I would > make blk_queue_enter smarter about whether to postpone a request. The > logic would go like this: > > If !blk_queue_pm_only: > Allow > If !BLK_MQ_REQ_PREEMPT: > Postpone > If q->rpm_status is RPM_ACTIVE: > Allow > If !BLK_MQ_REQ_PM: > Postpone > If q->rpm_status is RPM_SUSPENDED: > Postpone > Else: > Allow > > The assumption here is that the PREEMPT flag is set whenever the PM flag > is. Hi Alan, Although interesting, these solutions sound like workarounds to me. How about fixing the root cause by modifying the SCSI DV implementation such that it doesn't use scsi_device_quiesce() anymore()? That change would allow to remove BLK_MQ_REQ_PREEMPT / RQF_PREEMPT from the block layer and move these flags into the SCSI and IDE code. Thanks, Bart.
