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

[Alan Stern]

On Wed, Jun 14, 2023 at 04:35:50PM +0900, Damien Le Moal wrote:
> On 6/14/23 15:57, Hannes Reinecke wrote:
> > On 6/14/23 06:49, Damien Le Moal wrote:
> >> On 6/11/23 18:05, Joe Breuer wrote:
> >>> I'm the reporter of this issue.
> >>>
> >>> I just tried this patch against 6.3.4, and it completely fixes my
> >>> suspend/resume issue.
> >>>
> >>> The optical drive stays usable after resume, even suspending/resuming
> >>> during playback of CDDA content works flawlessly and playback resumes
> >>> seamlessly after system resume.
> >>>
> >>> So, from my perspective: Good one!
> >>
> >> In place of Bart's fix, could you please try this patch ?
> >>
> >> diff --git a/drivers/ata/libata-eh.c b/drivers/ata/libata-eh.c
> >> index b80e68000dd3..a81eb4f882ab 100644
> >> --- a/drivers/ata/libata-eh.c
> >> +++ b/drivers/ata/libata-eh.c
> >> @@ -4006,9 +4006,32 @@ static void ata_eh_handle_port_resume(struct
> >> ata_port *ap)
> >>          /* tell ACPI that we're resuming */
> >>          ata_acpi_on_resume(ap);
> >>
> >> -       /* update the flags */
> >>          spin_lock_irqsave(ap->lock, flags);
> >> +
> >> +       /* Update the flags */
> >>          ap->pflags &= ~(ATA_PFLAG_PM_PENDING | ATA_PFLAG_SUSPENDED);
> >> +
> >> +       /*
> >> +        * Resuming the port will trigger a rescan of the ATA device(s)
> >> +        * connected to it. Before scheduling the rescan, make sure that
> >> +        * the associated scsi device(s) are fully resumed as well.
> >> +        */
> >> +       ata_for_each_link(link, ap, HOST_FIRST) {
> >> +               ata_for_each_dev(dev, link, ENABLED) {
> >> +                       struct scsi_device *sdev = dev->sdev;
> >> +
> >> +                       if (!sdev)
> >> +                               continue;
> >> +                       if (scsi_device_get(sdev))
> >> +                               continue;
> >> +
> >> +                       spin_unlock_irqrestore(ap->lock, flags);
> >> +                       device_pm_wait_for_dev(&ap->tdev,
> >> +                                              &sdev->sdev_gendev);
> >> +                       scsi_device_put(sdev);
> >> +                       spin_lock_irqsave(ap->lock, flags);
> >> +               }
> >> +       }
> >>          spin_unlock_irqrestore(ap->lock, flags);
> >>   }
> >>   #endif /* CONFIG_PM */
> >>
> >> Thanks !
> >>
> > Well; not sure if that'll work out.
> > The whole reason why we initial a rescan is that we need to check if the
> > ports are still connected, and whether the devices react.
> > So we can't iterate the ports here as this is the very thing which gets
> > checked during EH.
> 
> Hmmm... Right. So we need to move that loop into ata_scsi_dev_rescan(),
> which itself already loops over the port devices anyway.
> 
> > We really should claim resume to be finished as soon as we can talk with
> > the HBA, and kick off EH asynchronously to let it finish the job after
> > resume has completed.
> 
> That is what's done already:
> 
> static int ata_port_pm_resume(struct device *dev)
> {
> 	ata_port_resume_async(to_ata_port(dev), PMSG_RESUME);
> 	pm_runtime_disable(dev);
> 	pm_runtime_set_active(dev);
> 	pm_runtime_enable(dev);
> 	return 0;
> }
> 
> EH is kicked by ata_port_resume_async() -> ata_port_request_pm() and it
> is async. There is no synchronization in EH with the PM side though. We
> probably should have EH check that the port resume is done first, which
> can be done in ata_eh_handle_port_resume() since that is the first thing
> done when entering EH.
> 
> The problem remains though that we *must* wait for the scsi device
> resume to be done before calling scsi_rescan_device(), which is done
> asynchronously from EH, as a different work. So that one needs to wait
> for the scsi side resume to be done.
> 
> I also thought of trigerring the rescan from the scsi side, but since
> the resume may be asynchronous, we could endup trigerring it with the
> ata side not yet resumed... That would only turn the problem around
> instead of solving it.

The order in which devices get resumed isn't arbitrary.  If the system 
is set up not to use async suspends/resumes then the order is always the 
same as the order in which the devices were originally registered (for 
resume, that is -- suspend obviously takes place in the reverse order).

So if you're trying to perform an action that requires two devices to be 
active, you must not do it in the resume handler for the device that was 
registered first.  I don't know how the ATA and SCSI pieces interact 
here, but regardless, this is a pretty strict requirement.

It should be okay to perform the action in the resume handler for the 
device that was registered second.  But if the two devices aren't in an 
ancestor-descendant relationship then you also have to call 
device_pm_wait_for_dev() (or use device links as Rafael mentioned) to 
handle the async case properly.

> Or... Why the heck scsi_rescan_device() is calling device_lock() ? This
> is the only place in scsi code I can see that takes this lock. I suspect
> this is to serialize either rescans, or serialize with resume, or both.
> For serializing rescans, we can use another lock. For serializing with
> PM, we should wait for PM transitions...
> Something is not right here.

Here's what commit e27829dc92e5 ("scsi: serialize ->rescan against 
->remove", written by Christoph Hellwig) says:

    Lock the device embedded in the scsi_device to protect against
    concurrent calls to ->remove.

That's the commit which added the device_lock() call.

Alan Stern