Problem with touchscreen events and grabs

[Thierry Reding]

Hi,

I've been seeing a very strange issue. Originally this was observed when
using a browser with an onscreen keyboard. It would sometimes happen
that the keys on the keyboard would get stuck and be repeatedly sent.

While trying to debug this, I came across a reliable way to reproduce it
using xwininfo. Basically I would run xwininfo and select the onscreen
keyboard. This would immediately result in the key being pressed and not
receiving a release event. Using other keys on the onscreen keyboard
would make them pressed as well, but never released either, resulting in
repeated keypresses received by the browser. It seems like X for some
reason believes that the press event is actually a release and vice-
versa.

In order to find out what exactly was going on, I fired up xev with the
window XID as reported by xwininfo. This would indeed show the repeated
key events sent to the onscreen keyboard's window. Strangely enough, if
xev is started without an existing window XID, generating touch events
in that window seems to "fix" the issue. The keyboard can be used
reliably again.

Furthermore, when running xwininfo and selecting the onscreen keyboard,
a second call to xwininfo would fail, saying it cannot grab the mouse.
This issue can be reliably reproduced independent of the onscreen
keyboard and works with any X window. So opening an xterm for instance,
then running xwininfo and selecting xterm will cause any subsequent
calls to xwininfo to fail. Running xev and generating touch events in
its window again fixes things.

It seems like the X server doesn't properly release the grab and gets
the touch down and up events mixed up. Note that all of this only
happens when using a touchscreen device. Performing the same tests using
a regular USB mouse to select the X window for xwininfo doesn't show the
same behaviour.

I'm using version 1.13 of the X server and xf86-input-evdev 2.7.3. Can
anybody else reproduce this?

If you need any more information I'd be happy to provide it.

Thierry
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