[Wayland-bugs] [Bug 69759] New: Touch points get out of sync with single touch devices; clients stop receiving events

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=69759

          Priority: medium
            Bug ID: 69759
          Assignee: wayland-bugs at lists.freedesktop.org
           Summary: Touch points get out of sync with single touch
                    devices; clients stop receiving events
          Severity: critical
    Classification: Unclassified
                OS: All
          Reporter: ullysses.a.eoff at intel.com
          Hardware: Other
            Status: NEW
           Version: unspecified
         Component: weston
           Product: Wayland

In corollary to Bug 67563, I can trigger weston to stop processing touch events
with a single touch device.  It's hard to trigger, but by rapidly tapping the
screen in random places, Weston eventually gets into a state where it stops
sending touch events to the clients.

After a little debugging, I found that input.c::notify_touch() gets invoked
with a value of WL_TOUCH_UP by evdev.c::evdev_process_key() twice in a row when
seat->num_tp==1 prior to the first WL_TOUCH_UP.  This results in seat->num_tp
getting decremented too many times, hence halting client touch notifications. 
In other words, the number of invocations of notify_touch(WL_TOUCH_DOWN) and
notify_touch(WL_TOUCH_UP) are not symmetric.  Beyond this, I'm not sure what
triggers evdev_process_key() to handle two BTN_TOUCH 0 events in a row... since
evtest BTN_TOUCH 1 and BTN_TOUCH 0 events appear to be symmetric.

evtest logs are forthcoming.

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