On 6/12/23 16:36, Kai-Heng Feng wrote: > On Mon, Jun 12, 2023 at 3:22 PM Damien Le Moal <dlemoal@xxxxxxxxxx> wrote: >> >> On 6/12/23 15:09, Hannes Reinecke wrote: >>> On 6/12/23 05:09, Damien Le Moal wrote: >>>> On 6/11/23 00:03, Bart Van Assche wrote: >>>>> On 6/10/23 06:27, Bagas Sanjaya wrote: >>>>>> On 6/10/23 15:55, Pavel Machek wrote: >>>>>>>>> #regzbot introduced: v5.0..v6.4-rc5 https://bugzilla.kernel.org/show_bug.cgi?id=217530 >>>>>>>>> #regzbot title: Waking up from resume locks up on SCSI CD/DVD drive >>>>>>>>> >>>>>>>> The reporter had found the culprit (via bisection), so: >>>>>>>> >>>>>>>> #regzbot introduced: a19a93e4c6a98c >>>>>>> Maybe cc the authors of that commit? >>>>>> >>>>>> Ah! I forgot to do that! Thanks anyway. >>>>> >>>>> Hi Damien, >>>>> >>>>> Why does the ATA code call scsi_rescan_device() before system resume has >>>>> finished? Would ATA devices still work with the patch below applied? >>>> >>>> I do not know the PM code well at all, need to dig into it. But your patch >>>> worries me as it seems it would prevent rescan of the device on a resume, which >>>> can be an issue if the device has changed. >>>> >>>> I am not yet 100% clear on the root cause for this, but I think it comes from >>>> the fact that ata_port_pm_resume() runs before the sci device resume is done, so >>>> with scsi_dev->power.is_suspended still true. And ata_port_pm_resume() calls >>>> ata_port_resume_async() which triggers EH (which will do reset + rescan) >>>> asynchronously. So it looks like we have scsi device resume and libata EH for >>>> rescan fighting each others for the scan mutex and device lock, leading to deadlock. >>>> >>>> Trying to recreate this issue now to confirm and debug further. But I suspect >>>> the solution to this may be best implemented in libata, not in scsi. >>>> This looks definitely related to this thread: >>>> >>>> https://lore.kernel.org/linux-scsi/7b553268-69d3-913a-f9de-28f8d45bdb1e@xxxxxxx/ >>>> >>>> Similaraly to your comment on that thread, having to look at >>>> dev->power.is_suspended is not ideal I think. What we need is to have ata and >>>> scsi pm resume be synchronized, but I am not yet 100% clear on the scsi layer side. >>>> >>> Which is my feeling, too. >>> libata runs rescan as part of the device discovery, so really it will >>> run after resume. And consequently resume really cannot wait for rescan >>> to finish. >>> >>> What I would be looking at is to decouple resume from libata device >>> rescan, and have resume to complete before libata EH runs. >> >> That is the case now, for the ata port at least, even though that is not super >> explicit, and not reliable. See ata_port_pm_resume(): I think that the call to >> EH in ata_port_pm_resume() -> ata_port_resume_async() -> ata_port_request_pm() >> -> ata_port_schedule_eh() should instead use a sync resume, leading to a sync EH >> call. >> >> That EH execution essentially does ata_eh_handle_port_resume(), which calls into >> the adapter resume operation. That in itself does not do much beside some >> registers accesses to wakeup the port. There should be no issues doing that >> synchronously. >> >> The problem is that after that is done, ata EH calls ata_std_error_handler() -> >> ata_do_eh() -> ata_eh_recover() -> ata_eh_revalidate_and_attach() -> >> schedule_work(&(ap->scsi_rescan_task)). And the rescan work calls >> scsi_rescan_device() (yet in another context than EH) which causes the problem >> when the scsi disk device has not been resumed yet (dev->power_is_suspended >> still true). >> >> So it really looks like the solution should be to have ata_scsi_dev_rescan() >> wait for the scsi device to resume first, but not sure how to do that with the >> pm API. Digging... > > Probably use dpm_wait_for_children()? Right now it's an internal PM API. But I am not sure if there is a relationship between ata_device and its scsi_device (dev->sdev)... Need to clarify that. > > Rafael, > What do you think? > > Kai-Heng > >> >>> >>> Cheers, >>> >>> Hannes >> >> -- >> Damien Le Moal >> Western Digital Research >> -- Damien Le Moal Western Digital Research
