On Sat, Aug 29, 2020 at 05:38:50PM -0700, Bart Van Assche wrote: > 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. That's a perfectly reasonable approach, but I have no idea how to do it. Any suggestions? Alan Stern
