On Thu, Feb 23, 2006 at 10:38:13AM -0500, Alan Stern wrote:
> On Wed, 22 Feb 2006, Greg KH wrote:
>
> > > Index: usb-2.6/drivers/base/dd.c
> > > ===================================================================
> > > --- usb-2.6.orig/drivers/base/dd.c
> > > +++ usb-2.6/drivers/base/dd.c
> > > @@ -72,6 +72,8 @@ int driver_probe_device(struct device_dr
> > > {
> > > int ret = 0;
> > >
> > > + if (!device_is_registered(dev))
> > > + return -ENODEV;
> > > if (drv->bus->match && !drv->bus->match(dev, drv))
> > > goto Done;
> > >
> > > Index: usb-2.6/drivers/base/bus.c
> > > ===================================================================
> > > --- usb-2.6.orig/drivers/base/bus.c
> > > +++ usb-2.6/drivers/base/bus.c
> > > @@ -367,6 +367,7 @@ int bus_add_device(struct device * dev)
> > >
> > > if (bus) {
> > > pr_debug("bus %s: add device %s\n", bus->name, dev->bus_id);
> > > + dev->is_registered = 1;
> > > device_attach(dev);
> > > klist_add_tail(&dev->knode_bus, &bus->klist_devices);
> > > error = device_add_attrs(bus, dev);
> > > @@ -393,7 +394,8 @@ void bus_remove_device(struct device * d
> > > sysfs_remove_link(&dev->kobj, "bus");
> > > sysfs_remove_link(&dev->bus->devices.kobj, dev->bus_id);
> > > device_remove_attrs(dev->bus, dev);
> > > - klist_remove(&dev->knode_bus);
> > > + klist_del(&dev->knode_bus);
> > > + dev->is_registered = 0;
> >
> > Don't we have a race between these two lines? How is that protected?
>
> Are you referring to the two lines that set dev->is_registered? There is
> no direct protection. However, one line is in bus_add_device() and the
> other is in bus_remove_device(); I've been assuming that any code
> responsible for adding and removing devices is serialized. That is, it
> won't ever try to remove a device before that device has been completely
> added.
Yes, that's probably safe to say.
> If that assumption isn't true, there are undoubtedly many other similar
> problems throughout the driver core. Like the calls to sysfs_create_link
> in bus_add_device and sysfs_remove_link in bus_remove_device.
>
> Or maybe you're referring to the device_is_registered() test in
> driver_probe_device(). That's synchronized with the call to
> device_release_driver() in bus_remove_device(), just below the portion you
> quoted, because both routines hold dev->sem. So even if the probe routine
> fails to see that the device has been unregistered, we are guaranteed that
> device_release_driver will unbind the device.
>
> If you're referring to two other lines, which lines are they?
The last 2 ones above, doing a klist_del() and then after that setting
is_registered to 0.
thanks,
greg k-h
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