On Tue, Apr 17, 2012 at 01:36:28PM -0700, Sarah Sharp wrote: > On Tue, Apr 17, 2012 at 03:22:39PM -0400, Alan Stern wrote: > > This patch (as154) fixes a self-deadlock that occurs when userspace > > writes to the bConfigurationValue sysfs attribute for a hub with > > children. The task tries to lock the bandwidth_mutex at a time when > > it already owns the lock: > > > > The attribute's method calls usb_set_configuration(), > > which calls usb_disable_device() with the bandwidth_mutex > > held. > > > > usb_disable_device() unregisters the existing interfaces, > > which causes the hub driver to be unbound. > > > > The hub_disconnect() routine calls hub_quiesce(), which > > calls usb_disconnect() for each of the hub's children. > > > > usb_disconnect() attempts to acquire the bandwidth_mutex > > around a call to usb_disable_device(). > > > > The solution is to make usb_disable_device() acquire the mutex for > > itself instead of requiring the caller to hold it. Then the mutex can > > cover only the bandwidth deallocation operation and not the region > > where the interfaces are unregistered. > > > > This has the potential to change system behavior slightly when a > > config change races with another config or altsetting change. Some of > > the bandwidth released from the old config might get claimed by the > > other config or altsetting, make it impossible to restore the old > > config in case of a failure. But since we don't try to recover from > > config-change failures anyway, this doesn't matter. > > This should be marked for stable kernels that contain the commit > fccf4e86200b8f5edd9a65da26f150e32ba79808 "USB: Free bandwidth when > usb_disable_device is called." > > That commit was marked for stable kernels as old as 2.6.32. Thanks for the information, I'll add it to the patch. greg k-h -- 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
