On Fri, Sep 16, 2011 at 3:15 PM, Jaikumar Ganesh <jaikumarg@xxxxxxxxx> wrote: > Hello, > > On Thu, Sep 15, 2011 at 5:28 PM, Jaikumar Ganesh <jaikumarg@xxxxxxxxx> wrote: >> Resending as the first email bounced. >> -------- >> Folks, >> There is a race condition in hid-magicmouse driver that I am >> encountering. In the probe function, we call magicmouse_setup_input >> after hid_hw_start which calls >> hidinput_connect. >> >> So if a userspace thread scans "/dev" to see if there is a new input >> device and on seeing the new magicmouse device added, makes the ioctl >> call EVCIOGBIT for EV_ABS or EV_KEY or any other type it will get >> wrong values as magicmouse_setup_input has not been called yet. >> >> So these keybits will change under the hood for the userspace program >> on an open file descriptor. >> >> I am able to reproduce this race condition easily. To verify the >> above, as a hack, I called magicmouse_setup_input just before calling >> input_register_device in hidp_connect and things were fine. >> >> We were not using hidp-input parser but in the following commit we >> moved to it which introduced the race condition: >> >> commit 64eb105d7f92fa48798106ac0d8bf17668eb2524 >> Author: Michael Poole <mdpoole@xxxxxxxxxxx> >> Date: Fri Sep 24 13:58:18 2010 +0200 >> >> HID: magicmouse: Use hid-input parsing rather than bypassing it >> >> Any pointers for a clean fix ? Do we want to add a new field to >> hid_driver structure so that we can use it to call from hid-input to >> indicate parsing is done before the input device is registered ? > > I had a look at the hid-apple.c driver which also has a setup_input function. > > But that function is called inside input_mapping - so that gets called > every single time input_mapping is called. > That will fix this issue too, but seems like an overkill to call > magicmouse_setup_input every single time in input_mapping. Perhaps it is worth doing that, but adding a flag so that the bulk of magicmouse_setup_input() only runs once. (I can write and test a patch on Monday, once I get network access at home.) Michael -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
