Messages in this thread | | | Date | Tue, 29 Jun 2021 14:23:28 +0800 | From | Can Guo <> | Subject | Re: [PATCH v4 06/10] scsi: ufs: Remove host_sem used in suspend/resume |
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On 2021-06-29 01:31, Bart Van Assche wrote: > On 6/28/21 1:17 AM, Can Guo wrote: >> On 2021-06-25 01:11, Bart Van Assche wrote: >>> On 6/23/21 11:31 PM, Can Guo wrote: >>>> Using back host_sem in suspend_prepare()/resume_complete() won't >>>> have >>>> this problem of deadlock, right? >>> >>> Although that would solve the deadlock discussed in this email >>> thread, it >>> wouldn't solve the issue of potential adverse interactions of the UFS >>> error handler and the SCSI error handler running concurrently. >> >> I think I've explained it before, paste it here - >> >> ufshcd_eh_host_reset_handler() invokes ufshcd_err_handler() and >> flushes it, >> so SCSI error handler and UFS error handler can safely run together. > > That code path is the exception. Do you agree that the following three > functions all invoke the ufshcd_err_handler() function asynchronously? > * ufshcd_uic_pwr_ctrl() > * ufshcd_check_errors() > * ufshcd_abort() >
I agree, but I don't see what's wrong with that. Any context can invoke ufs error handler asynchronously and ufs error handler prepare makes sure error handler can work safely, i.e., stopping PM ops/gating/scaling in error handler prepare makes sure no one shall call ufshcd_uic_pwr_ctrl() ever again. And ufshcd_check_errors() and ufshcd_abort() are OK to run concurrently with UFS error handler.
>>> How about using the >>> standard approach for invoking the UFS error handler instead of using >>> a custom >>> mechanism, e.g. by using something like the (untested) patch below? >>> This >>> approach guarantees that the UFS error handler is only activated >>> after >>> all >>> pending SCSI commands have failed or timed out and also guarantees >>> that no new >>> SCSI commands will be queued while the UFS error handler is in >>> progress (see >>> also scsi_host_queue_ready()). >> >> Per my understanding, SCSI error handling is scsi cmd based, meaning >> it >> only works when certain SCSI cmds failed [ ... ] > That is not completely correct. The SCSI error handler is activated if > either all pending commands have failed or if it is scheduled > explicitly. Please take a look at the host_eh_scheduled member > variable, > how it is used and also at scsi_schedule_eh(). The scsi_schedule_eh() > function was introduced in 2006 and that the ATA code uses it since > then > to activate the SCSI error handler even if no commands are pending. See > also the patch "SCSI: make scsi_implement_eh() generic API for SCSI > transports". > >> However, most UFS (UIC) errors happens during gear scaling, clk gating >> and suspend/resume (due to power mode changes and/or hibern8 >> enter/exit), during which there is NO scsi cmds in UFS driver at all >> (because these contexts start only when there is no ongoing data >> transactions). > > Activating the SCSI error handler if no SCSI commands are in progress > is > supported by scsi_schedule_eh(). > >> Thus, scsi_unjam_host() won't even call scsi_eh_ready_devs() because >> scsi_eh_get_sense() always returns TRUE in these cases (eh_work_q is >> empty). > > Please take another look at the patch in my previous message. There is > a > scsi_transport_template instance in that patch. The eh_strategy_handler > defined in a SCSI transport template is called *instead* of > scsi_unjam_host(). In other words, scsi_unjam_host() won't be called if > my patch would be applied to the UFS driver. > > Please let me know if you need more information.
Sorry that I missed the change of scsi_transport_template() in your previous message. I can understand that you want to invoke UFS error hander by invoking SCSI error handler, but I didn't go that far because I saw you changed pm_runtime_get_sync() to pm_runtime_get_noresume() in ufs error handler prepare. How can that change make sure that the device is not suspending or resuming while error handler is running?
Thanks,
Can Guo.
> > Bart.
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