From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751447AbWBWPiS (ORCPT ); Thu, 23 Feb 2006 10:38:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751430AbWBWPiS (ORCPT ); Thu, 23 Feb 2006 10:38:18 -0500 Received: from iolanthe.rowland.org ([192.131.102.54]:52111 "HELO iolanthe.rowland.org") by vger.kernel.org with SMTP id S1751447AbWBWPiS (ORCPT ); Thu, 23 Feb 2006 10:38:18 -0500 Date: Thu, 23 Feb 2006 10:38:13 -0500 (EST) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Greg KH cc: James Bottomley , Kernel development list Subject: Re: [PATCH] driver core: better reference counting for klists In-Reply-To: <20060223050525.GA8046@kroah.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org 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