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

[Saravana Kannan]

On Mon, Feb 15, 2021 at 11:08 AM Geert Uytterhoeven
<geert@xxxxxxxxxxxxxx> wrote:
>
> Hi Saravana,
>
> On Mon, Feb 15, 2021 at 7:27 PM Saravana Kannan <saravanak@xxxxxxxxxx> wrote:
> > On Mon, Feb 15, 2021 at 6:59 AM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
> > > On Mon, Feb 15, 2021 at 12:16 PM Geert Uytterhoeven
> > > <geert+renesas@xxxxxxxxx> 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@xxxxxxxxx>
> > >
> > > Good catch:
> > >
> > > Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> >
> > 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.

Thanks for the explanation. Maybe add more details like this to the
commit text or in the code?

For the code:
Reviewed-by: Saravana Kanna <saravanak@xxxxxxxxxx>

-Saravana

>
> > > > +++ 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@xxxxxxxxxxxxxx
>
> 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