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I've been seeing sporadic (anywhere from once every few days to 3-4
times a day) crashes and freezes in X. The problematic behaviour isn't
always the same, but I chose a particular incident to debug, and found
that X was segfaulting in updateMotionHistory, on line 575 of
dix/getevents.c.
After some further investigation, I found that the bug was being
triggered when a SIGIO was received in DeepCopyPointerClasses, between
the AllocValuatorClass call (line 540) and updating the to->valuator
pointer (line 545). AllocValuatorClass calls realloc() on to->valuator,
so between these lines, it's not guaranteed to point to allocated
memory.
It seems the SIGIO handler is calling updateMotionHistory, which is
reading the memory pointed to by to->valuator and getting a wrong value
for last_motion, which updates buff to point to wildly the wrong place
and thus generates a segfault when a memcpy() is done into buff.
I am attaching a patch which I've been running on that machine for the
past three days, and haven't yet observed any more crashing or freezing
behaviour. The patch simply calls OsBlockSIGIO while
DeepCopyDeviceClasses is in progress, as the state of the X server's
device data structures is not guaranteed to be in a consistent state
during that time.
Debian bug#744303 <https://bugs.debian.org/744303>
Signed-off-by: Julien Cristau <jcristau@debian.org>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
(cherry picked from commit
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|---|---|---|
| composite | ||
| config | ||
| damageext | ||
| dbe | ||
| dix | ||
| doc | ||
| dri3 | ||
| exa | ||
| fb | ||
| glx | ||
| hw | ||
| include | ||
| m4 | ||
| man | ||
| mi | ||
| miext | ||
| os | ||
| present | ||
| pseudoramiX | ||
| randr | ||
| record | ||
| render | ||
| test | ||
| Xext | ||
| xfixes | ||
| Xi | ||
| xkb | ||
| .dir-locals.el | ||
| .gitignore | ||
| autogen.sh | ||
| configure.ac | ||
| COPYING | ||
| devbook.am | ||
| docbook.am | ||
| fix-miregion | ||
| fix-miregion-private | ||
| fix-patch-whitespace | ||
| fix-region | ||
| Makefile.am | ||
| manpages.am | ||
| README | ||
| xorg-server.m4 | ||
| xorg-server.pc.in | ||
| xserver.ent.in | ||
X Server
The X server accepts requests from client applications to create windows,
which are (normally rectangular) "virtual screens" that the client program
can draw into.
Windows are then composed on the actual screen by the X server
(or by a separate composite manager) as directed by the window manager,
which usually communicates with the user via graphical controls such as buttons
and draggable titlebars and borders.
For a comprehensive overview of X Server and X Window System, consult the
following article:
http://en.wikipedia.org/wiki/X_server
All questions regarding this software should be directed at the
Xorg mailing list:
http://lists.freedesktop.org/mailman/listinfo/xorg
Please submit bug reports to the Xorg bugzilla:
https://bugs.freedesktop.org/enter_bug.cgi?product=xorg
The master development code repository can be found at:
git://anongit.freedesktop.org/git/xorg/xserver
http://cgit.freedesktop.org/xorg/xserver
For patch submission instructions, see:
http://www.x.org/wiki/Development/Documentation/SubmittingPatches
For more information on the git code manager, see:
http://wiki.x.org/wiki/GitPage