Issue 688: Touch often crashes the Debian X-Server

Reported by Nikolaus Schaller, Jun 14, 2015

this is a quite old bug known for a while, but no solution found.
If we use Xserver from Debian Wheezy it crashes randomly as soon as 
the touch is pressed. Some times it works fine for a while so that 
you can operate menus etc.
The reason is completely unknown.
The error message from X11 is not helpful: SEGFAULT.
It did start to appear at kernel 3.15 or 3.16 but it is not exactly 
known when it happened.
Some theories:
* it is obvious that it is some touch event that the X server does 
misinterpret
* the x-server was compiled for a 3.2 kernel
* so there might have been some additional data field or the event 
handler might optimize some events away where X leaves an 
initialized data field
* that is taken as some index and therefore segfaults
* it is also not obviously dependent on some specific position to 
touch
The effect has been observed on all different CPUs we have: OMAP3, 
OMAP5, OpenPandora, GTA04, AM3358 (BeagleBone).

Comment 1 by Nikolaus Schaller, Sep 10, 2015

It appears that it is NOT a touch screen event, but a deep kernel 
problem with delivering signal() with ARM/thumb mode switching.
It appears that this is only used heavily by the Xserver and active 
in the kernel only for MULTI_ARCH_V6. So we temporarily disable CPU 
V6 (N800.
This change can be reverted as soon as a real patch for the signal.c 
code is upstream.

Status: Accepted
Owner: hns

Comment 2 by Nikolaus Schaller, Oct 24, 2015

Has now become mainline (and even backported). So we finally have 
fixed this issue!

Status: Fixed

Letux Kernel