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. Rafael, What do you think? Kai-Heng > > > > > Cheers, > > > > Hannes > > -- > Damien Le Moal > Western Digital Research >
