My findings about this bug, so far:
The problem is that there's a mouse grab by compiz at some point, that is
caused by the XGrabButton call in updatePassiveButtonGrabs in window.cpp:
[...]
else
{
/* Grab all buttons */
XGrabButton (screen->dpy (),
AnyButton,
AnyModifier,
serverFrame, false,
ButtonPressMask | ButtonReleaseMask | ButtonMotionMask,
GrabModeSync,
GrabModeAsync,
None,
None);
[...]
(I verified that this by replacing the default mouse pointer shape with
the XC_pirate: when the bug occured the pointer changed to a pirate
head.)
This grab is used by compiz for windows that don't have the focus: when
the user clicks inside a window, compiz grabs the mouse so that the
mouse events are handled by compiz and not by the window. That's useful
in case someone needs to raise a window by clicking on it as opposed to
clicking on its frame for example.
The XGrabButton uses the GrabModeSync. According to the XGrabPointer manpage:
if the pointer mode is GrabModeSync the state of the pointer, as seen by client
applications, appears to freeze, and the X server generates no further pointer
events until the grabbing client calls XAllowEvents or until the pointer grab
is released. Actual pointer changes are not lost while the pointer is frozen;
they are simply queued in the server for later processing.
(that's why we can't click anywhere after this grab occurs)
I believe that a race condition related to the grabs/ungrabs is
triggered here and it's difficult to be found because the passive grab
is initiated by the xserver when the conditions set by the XGrabButton
call are satisfied, so backtraces are not really helpful.
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https://bugs.launchpad.net/bugs/1310518
Title:
Touch screen and touchpad lost click function after quickly tapped
dash home repeatly by touch screen
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