Re: [PATCH] driver core: Fix double failed probing with fw_devlink=on

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Saravana,

On Mon, Feb 15, 2021 at 7:27 PM Saravana Kannan <saravanak@google.com> wrote:
> On Mon, Feb 15, 2021 at 6:59 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
> > On Mon, Feb 15, 2021 at 12:16 PM Geert Uytterhoeven
> > <geert+renesas@glider.be> wrote:
> > > With fw_devlink=permissive, devices are added to the deferred probe
> > > pending list if their driver's .probe() method returns -EPROBE_DEFER.
> > >
> > > With fw_devlink=on, devices are added to the deferred probe pending list
> > > if they are determined to be a consumer,
>
> If they are determined to be a consumer or if they are determined to
> have a supplier that hasn't probed yet?

When the supplier has probed:

    bus: 'platform': driver_probe_device: matched device
e6150000.clock-controller with driver renesas-cpg-mssr
    bus: 'platform': really_probe: probing driver renesas-cpg-mssr
with device e6150000.clock-controller
    PM: Added domain provider from /soc/clock-controller@e6150000
    driver: 'renesas-cpg-mssr': driver_bound: bound to device
'e6150000.clock-controller'
    platform e6055800.gpio: Added to deferred list
    [...]
    platform e6020000.watchdog: Added to deferred list
    [...]
    platform fe000000.pcie: Added to deferred list

> > > which happens before their
> > > driver's .probe() method is called.  If the actual probe fails later
> > > (real failure, not -EPROBE_DEFER), the device will still be on the
> > > deferred probe pending list, and it will be probed again when deferred
> > > probing kicks in, which is futile.
> > >
> > > Fix this by explicitly removing the device from the deferred probe
> > > pending list in case of probe failures.
> > >
> > > Fixes: e590474768f1cc04 ("driver core: Set fw_devlink=on by default")
> > > Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> >
> > Good catch:
> >
> > Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> The issue is real and needs to be fixed. But I'm confused how this can
> happen. We won't even enter really_probe() if the driver isn't ready.
> We also won't get to run the driver's .probe() if the suppliers aren't
> ready. So how does the device get added to the deferred probe list
> before the driver is ready? Is this due to device_links_driver_bound()
> on the supplier?
>
> Can you give a more detailed step by step on the case you are hitting?

The device is added to the list due to device_links_driver_bound()
calling driver_deferred_probe_add() on all consumer devices.

> > > +++ b/drivers/base/dd.c
> > > @@ -639,11 +639,13 @@ static int really_probe(struct device *dev, struct device_driver *drv)
> > >         case -ENXIO:
> > >                 pr_debug("%s: probe of %s rejects match %d\n",
> > >                          drv->name, dev_name(dev), ret);
> > > +               driver_deferred_probe_del(dev);
> > >                 break;
> > >         default:
> > >                 /* driver matched but the probe failed */
> > >                 pr_warn("%s: probe of %s failed with error %d\n",
> > >                         drv->name, dev_name(dev), ret);
> > > +               driver_deferred_probe_del(dev);
> > >         }
> > >         /*
> > >          * Ignore errors returned by ->probe so that the next driver can try

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds