On Wed, Nov 18, 2009 at 8:31 AM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > On Wed, 18 Nov 2009, Jiri Kosina wrote: > >> On Tue, 17 Nov 2009, Russ Dill wrote: >> >> > Many usb drivers that create character devices use "struct >> > usb_class_driver", a set of fops, and a usb_find_interface in their >> > open call. A prime example is drivers/usb/usb-skeleton.c. A race >> > occurs when userspace receives a hotplug event for the addition for >> > the interface and then opens the associated device file before the >> > device is added to the driver's klist_devices. >> > >> > The usb core senses a new usb device (usb_new_device) and calls >> > device_add. This eventually gets down to really_probe and the >> > usb-skeleton probe function, skel_probe. skel_probe calls >> > usb_register_dev() which registers the associated character device for >> > skel_class. The hotplug events for the class device get emitted. >> > >> > User space receives the hotplug event for the class device, makes the >> > device node and notifies another program that opens the device node. >> > The program opens the device node which calls into usb_open and then >> > skel_open. skel_open calls usb_find_interface. usb_find_interfaces >> > searches the klist_devices of skel_driver, finds no device associated >> > with the minor number and returns NULL. skel_open returns -ENODEV. >> > >> > Control returns to really_probe and really_probe calls driver_bound >> > which adds the device to the list of devices associated with >> > skel_driver (klist_devices). >> > >> > I'm not sure what the right way to solve this is. A call to >> > wait_for_device_probe() in the skel_open call before calling >> > usb_find_interface fixes the problem, but it is a rather large hammer. > > I think the proper answer is for usb_find_interface() to use > bus_for_each_dev() instead of driver_for_each_device(). > This would work, bus_find_device would probably be a better match. -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
