On Fri, 23 Apr 2010, Eric W. Biederman wrote: > Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> writes: > > > Eric: > > > > This looks like it's up your alley. > > I took a quick look at the code and this actually looks like a > legitimate warning. > > I may be wrong but it looks like the write method > set_bConfigurationValue disable it's current usb device and attempts > to remove the bConfigurationValue sysfs file, and in doing so waits > for the write to complete. aka deadlock. No, it doesn't do that. The write method might _unconfigure_ the USB device, but it would not disable the device and it would not try to remove the bConfigurationValue file. Here's the relevant part of the stack dump: [<ffffffff811785ba>] sysfs_addrm_finish+0x36/0x55 [<ffffffff81176818>] sysfs_hash_and_remove+0x53/0x6a [<ffffffff811799b1>] sysfs_remove_group+0x91/0xca [<ffffffff812f2b45>] dpm_sysfs_remove+0x19/0x1b [<ffffffff812ebbdd>] device_del+0x4c/0x1ab [<ffffffff812ebd70>] device_unregister+0x34/0x5b [<ffffffff8135207f>] usb_remove_ep_devs+0x23/0x2f [<ffffffff8134adb9>] remove_intf_ep_devs+0x37/0x4d [<ffffffff8134b00b>] usb_disable_device+0xc4/0x1d8 [<ffffffff8134cd62>] usb_set_configuration+0x28d/0x685 [<ffffffff8107df48>] ? mark_held_locks+0x52/0x70 [<ffffffff8147ace1>] ? _raw_spin_unlock_irqrestore+0x47/0x56 [<ffffffff813519ef>] set_bConfigurationValue+0x5e/0x88 This shows that set_bConfigurationValue indirectly calls device_unregister() not for its own device, but for various children (the interface ep devices). Not only are these different device structures, they don't even have a bConfigurationValue attribute. (Note that it _is_ possible for a write to bConfigurationValue for one device to unregister a child device that _does_ have a bConfigurationValue attribute. But that's not what occurred here.) > This might also be one of the false positives I reworked the code in > 2.6.34 to fix, by putting different attributes in different sysfs > classes but it doesn't look like it. Are you sure? It kind of looks like it to me. Maybe the fix wasn't present in the kernel Dave was running. Alan Stern -- 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
