On Thu, 2013-01-24 at 13:58 +0000, Karl Relton wrote: > On Tue, 2013-01-15 at 20:27 +0000, Karl Relton wrote: > > > The end result (for the user) is that even when the bluetooth > > > mouse/keyboard is re-added, Xorg ignores it - thinking it is some > > hoax > > > duplicate device. The keyboard/mouse is then non-operational. > > > > > > > Instrumenting the code suggests that the issue arises in a race > > between: > > > > hidp_session() in bluetooth/hidp/core.c > > > > and > > > > hci_unregister_dev() in bluetooth/hci_core.c > > > > ... > > > > I can't figure out why there is such a delay for > > input_unregister_device(). > > > The power_supply system seems to be triggering a lookup of battery > 'capacity' in the input device. This calls into the driver, which deep > down invokes more code in the 'hidp' module: hidp_get_raw_report() > > This function tries to communicate with the bluetooth device (keyboard > in my case), but because the device is being 'torn down' such > communication fails. Accordingly hidp_get_raw_report has a 5 second > timeout ... so this function stalls for 5 seconds until that timeout > occurs. > > > I would guess that for some reason, removing the 'hid' or associated > 'input' device is leading to the power_supply code wanting to lookup the > battery capacity which introduces a 5 second wait. This would delay > hidp_session by 5 seconds ... in the mean time allowing > hci_unregister_dev() to win the race and hence the hci device is removed > before the input & hid devices. > device_del is done on the battery device, called from hidinput_cleanup_battery in hid-input.c. This will generate a uevent which has the power_supply attributes added, which invokes power_supply_show_property for 'capacity' which invokes the hidp_get_raw_report (which stalls for 5 seconds). Back in the days of linux 3.2, hid-input.c did not have any support for batteries, so this chain of calls was never made, hence the race was won by hidp_session() because it didn't have the 5 second delay injected. Now with battery support added, the problem is manifest. -- I think hidp_get_raw_report should abort if the devices is being 'torn down' (and so not go into the 5 second wait). But also the race between the two functions needs sorting, since sooner or later someone else will get unlucky. -- 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
