Re: Fwd: Waking up from resume locks up on sr device

[Kai-Heng Feng]

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
>