Messages in this thread | | | Date | Thu, 23 Feb 2006 10:38:13 -0500 (EST) | From | Alan Stern <> | Subject | Re: [PATCH] driver core: better reference counting for klists |
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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.
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?
Alan Stern
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