Re: patch bus_add_device-losing-an-error-return-from-the-probe-method.patch added to gregkh-2.6 tree

[Greg KH]

On Tue, Apr 04, 2006 at 02:00:48PM -0700, Greg KH wrote:
> On Tue, Apr 04, 2006 at 04:23:43PM -0400, Dmitry Torokhov wrote:
> > On 4/4/06, gregkh@xxxxxxx <gregkh@xxxxxxx> wrote:
> > >
> > > --- gregkh-2.6.orig/drivers/base/bus.c
> > > +++ gregkh-2.6/drivers/base/bus.c
> > > @@ -372,14 +372,17 @@ int bus_add_device(struct device * dev)
> > >
> > >        if (bus) {
> > >                pr_debug("bus %s: add device %s\n", bus->name, dev->bus_id);
> > > -               device_attach(dev);
> > > +               error = device_attach(dev);
> > > +               if (error < 0)
> > > +                       goto exit;
> > 
> > I do not believe that this is correct. The fact that _some_ driver
> > failed to attach to a device does not necessarily mean that device
> > itself does not exist. While this assuption might work for platform
> > devices it won't work for other busses.
> 
> Hm, no, I unwound this mess, and found the following:
> 
>  - bus_add_device() calls device_attach()
>  - device_attach() calls bus_for_each_drv() for every driver on the bus
>  - bus_for_each_drv() walks all drivers on the bus and calls
>    __device_attach() for every individual driver
>  - __device_attach() calls driver_probe_device() for that driver and device
>  - driver_probe_device() calls down to the probe() function for the
>    driver, passing it that driver, if match() for the bus matches this
>    device.
>  - if that probe() function returns -ENODEV or -ENXIO[1] then the error
>    is ignored and 0 is returned, causing the loop to continue to try
>    more drivers
>  - if the probe() function returns any other error code, it is
>    propagated up, all the way back to bus_add_device.
>  - if the probe() function returns 0, the device is bound to the driver,
>    and it returns 0.  Hm, looks like we continue to loop here too, we
>    could probably stop now that we have bound a driver to the device.
> 
> So, I'm pretty sure that this is safe and should work just fine.  To be
> sure, let me go reboot my box with this change on it after I finish this
> email :)

Yup, things still seem to work properly for me.  The patch will show up
in the next -mm for others to beat on...

thanks,

greg k-h
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