Richard,
I never got any response (positive or negative) from you
when I submitted my fix for the SIGSEGV problem that CTWM
suffers on occasion. It happens that I've been out of work
and I'd like to be able to show that I've not been idle
during that time so I'm hoping to be able to say that my
patch was accepted.
Now, obviously, my employment situation is strictly my own
problem and in no way obligates you to do anything, but since
the patch is straightforward and the benefit (both to CTWM
users as well as to my "street cred") is real, I ask once
again that you accept the patch. Thanks.
--Michael O'Donnell
###### REPEATED POSTING FROM JULY, INCLUDING PATCH:
For those who asked, here are excerpts from emails I've sent
to Debian regarding the CTWM crashes that I've repaired.
#################################################################
A brief sketch of typical usage and failure mode:
I am running CTWM with eight workspaces (most are populated)
and switching workspaces fairly often. The most active
X apps are xterm, Firefox, exmh and mahjongg. I typically
have several Firefox windows open, each of which has multiple
tabs active, sometimes dozens. Failure seemed most often
to happen immediately after I switched workspaces to one
containing a Firefox window with a *LOT* of tabs open.
I've not seen it even once since this I made this fix.
Note that I was usually able to recover my entire X session
and continue without harm if I could manage to launch a
new instance of CTWM from the console or an SSH session.
Until I patched my CTWM I actually had a shell loop right
inside my .xsession file that would automatically relaunch
CTWM when it crashed, so I was able to live with it for
several years before finally getting fed up and fixing it!
#################################################################
Here's a bit of GDB output to illustrate the specific
fauilt that was constantly occurring before I fixed it:
Program received signal SIGSEGV, Segmentation fault.
0x0805f131 in PlaceOntop (ontop=8, where=0) at menus.c:3756
3756 for (t = Scr->TwmRoot.next; t != NULL; t = t->next) {
(gdb) where
#0 0x0805f131 in PlaceOntop (ontop=8, where=0) at menus.c:3756
#1 0x0805f24b in RaiseWindow (tmp_win=0x83343a0) at menus.c:3787
#2 0x0806ab10 in AutoRaiseWindow (tmp=0x83343a0) at events.c:218
#3 0x0807096f in HandleEvents () at events.c:547
#4 0x0804e3a7 in main (argc=2, argv=0xbff491a4, environ=0xbff491b0)
at ctwm.c:1027
(gdb) print Scr
$2 = (ScreenInfo *) 0x0
#################################################################
To: Debian Bug Tracking System <[email protected]>
Date: Tue, 06 Mar 2012 15:42:25 -0500
Subject: debianBug#662860 - ctwm: SIGSEGV when changing workspaces
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=662860
Package: ctwm
Version: 3.7-3.2
Severity: important
Tags: upstream patch
Dear Maintainer,
I'm a longtime CTWM user who finally got tired of the random
crashes that occur, typically when I'm switching workspaces.
I can sometimes go for a month without seeing them and sometimes
it happens several times a day. I've analyzed this to the point
where I can see that code in DispatchEvent() is occasionally
leaving the global Scr pointer NULL which causes a SIGSEGV on
our next pass through the loop in HandleEvents().
I've provided a patch that adds a few lines of defensive code
which seems to have improved the situation, though I have not
analyzed the root cause, which appears to be that, for unknown
reasons, either XFindContext() or FindScreenInfo() seem to be
unable to return the answer expected of them.
--Michael O'Donnell
BEGIN PATCH:
--- events.c.b0rken 2012-03-06 15:10:42.093677349 -0500
+++ events.c 2012-03-06 15:19:52.369161662 -0500
@@ -435,21 +435,25 @@
*/
Bool DispatchEvent2 (void)
{
Window w = Event.xany.window;
StashEventTime (&Event);
+ ScreenInfo *lastScr = Scr; /* XXX_MIKE - assume Scr OK on entry... */
if (XFindContext (dpy, w, TwmContext, (XPointer *) &Tmp_win) == XCNOENT)
Tmp_win = NULL;
if (XFindContext (dpy, w, ScreenContext, (XPointer *)&Scr) == XCNOENT) {
Scr = FindScreenInfo (WindowOfEvent (&Event));
}
dumpevent(&Event);
- if (!Scr) return False;
+ if (!Scr) {
+ Scr = lastScr; /* XXX_MIKE - try not to leave Scr NULL */
+ return False;
+ }
if (Scr->Root != Scr->RealRoot) FixRootEvent (&Event);
#ifdef SOUNDS
play_sound(Event.type);
#endif
@@ -473,21 +477,25 @@
*/
Bool DispatchEvent (void)
{
Window w = Event.xany.window;
StashEventTime (&Event);
+ ScreenInfo *lastScr = Scr; /* XXX_MIKE - assume Scr OK on entry... */
if (XFindContext (dpy, w, TwmContext, (XPointer *) &Tmp_win) == XCNOENT)
Tmp_win = NULL;
if (XFindContext (dpy, w, ScreenContext, (XPointer *)&Scr) == XCNOENT) {
Scr = FindScreenInfo (WindowOfEvent (&Event));
}
dumpevent(&Event);
- if (!Scr) return False;
+ if (!Scr) {
+ Scr = lastScr; /* XXX_MIKE - try not to leave Scr NULL */
+ return False;
+ }
if (captive) {
if ((Event.type == ConfigureNotify) && (Event.xconfigure.window ==
Scr->CaptiveRoot)) {
ConfigureRootWindow (&Event);
return (False);
END PATCH
-- System Information:
Debian Release: wheezy/sid
APT prefers testing
APT policy: (990, 'testing'), (500, 'unstable')
Architecture: i386 (i686)
Kernel: Linux 3.1.0 (SMP w/2 CPU cores)
Locale: LANG=en_US, LC_CTYPE=en_US (charmap=ISO-8859-1)
Shell: /bin/sh linked to /bin/bash
Versions of packages ctwm depends on:
ii libc6 2.13-26
ii libice6 2:1.0.7-2
ii libjpeg8 8d-1
ii librplay3 3.3.2-14
ii libsm6 2:1.2.0-2
ii libx11-6 2:1.4.4-4
ii libxext6 2:1.3.0-3
ii libxmu6 2:1.1.0-3
ii libxpm4 1:3.5.9-4
ii libxt6 1:1.1.1-2
ii m4 1.4.16-2
ii x11-common 1:7.6+11
ctwm recommends no packages.
ctwm suggests no packages.
-- Configuration Files:
/etc/X11/ctwm/system.ctwmrc [Errno 2] No such file or directory:
u'/etc/X11/ctwm/system.ctwmrc'
