[gdm-list] Re: PostSession script support fades out from 2.4 to 2.6?

["Jerry G. DeLapp" <jgd-gdm kodiak lanl gov>]

On Monday 15 August 2005 06:20 pm, Jerry G. DeLapp wrote:
>
> Spent the past few days dusting off my last experience with setjmp (about 2
> decades ago), adding gdm_debug calls in various places, and tweaking code.
> Found the following.  These are based upon the RHEL4 source, which is a
> patched up version of 2.6.0.5.
>
> 1) There's a 'session_started = FALSE' at the beginning of
> gdm_slave_session_stop.  When I started adding debug code it became
> apparent that this was the line that was turning off session_started for
> the longjmp target code.  I'm not sure it should even be there.
>
> 2) You never get to the postsession script because:  The call to
> gdm_server_whack_clients in gdm_slave_session_stop will trigger an
> xioerror.
>
> The user has crashed X with ctl-alt-backspace,  and whack_clients tries to
> access the X server.  The resulting xioerror event then vectors you via the
> xioerror handler to the quick exit code.  That is, more than one crash
> handler gets called and the second one terminates the correct execution of
> the original exit handler.  The problem code has comments that say "fix
> #126071".
>
> I was able to get back to the "old, correct" behavior by commenting the
> code line in (1) and, later, after I understood the handler behavior,
> adding another setjmp that caused the xioerror to be ignored during the
> call to gdm_server_whack_clients.
>
> I still need to check whether the added setjmp code means that item 1 is
> not really an issue, and to create a patch that doesn't have the fourteen
> or so additional gdm_debug and printf patches I created.  I'll post the
> patch for further discussion when I've done that, probably tomorrow.
>
> J

Item 1 turned out to not matter once I implemented the fix to item 2.  
Attached for discussion is a patch against 2.6.0.8 source as modified by 
FC4's rpm.

J

--- gdm-2.6.0.8.orig/daemon/slave.c	2005-08-19 13:32:00.000000000 -0600
+++ gdm-2.6.0.8/daemon/slave.c	2005-08-19 13:48:43.000000000 -0600
@@ -195,6 +195,7 @@
 /* Local prototypes */
 static gint     gdm_slave_xerror_handler (Display *disp, XErrorEvent *evt);
 static gint     gdm_slave_xioerror_handler (Display *disp);
+static gint     gdm_slave_ignore_xioerror_handler (Display *disp);
 static void	gdm_slave_run (GdmDisplay *display);
 static void	gdm_slave_wait_for_login (void);
 static void     gdm_slave_greeter (void);
@@ -231,6 +232,8 @@
 
 /* for signals that want to exit */
 static Jmp_buf slave_start_jmp;
+/* for handling xioerror during ctl-alt-bs */
+static Jmp_buf ignore_xioerror_jmp;
 static gboolean return_to_slave_start_jmp = FALSE;
 static gboolean already_in_slave_start_jmp = FALSE;
 static char *slave_start_jmp_error_to_print = NULL;
@@ -4388,8 +4391,27 @@
        This is to fix #126071, that is kill processes that may still hold open
        fd's in the home directory to allow a clean unmount.  However note of course
        that this is a race. */
+    /* FIX HACK: We will get an xioerror out of whack clients if the user crashed X with ctl-alt-backspace.
+       So, we need to ignore xioerror while we do this. Otherwise, we end up in a longjmp to quick_exit
+       which will prevent things like PostSession scripts from processing */
+    switch (Setjmp (ignore_xioerror_jmp)) {
+    case 0:
+       /* Having just set the jump point, activate the error handler that returns us to the next case */
+       XSetIOErrorHandler (gdm_slave_ignore_xioerror_handler);
+       break;
+    default:
+       /* Here means we saw an xioerror and ignored it. */
+       /* xioerror will cause this to drop back into whack_clients, but I think that's OK
+          because I haven't seen it do so more than once */
+       gdm_debug("gdm_slave_session_stop: back here from xioerror");
+       break;
+    };
+
     gdm_server_whack_clients (d);
 
+    /* Now we should care about xioerror once again??? */
+    XSetIOErrorHandler (gdm_slave_xioerror_handler);
+
 #if defined(_POSIX_PRIORITY_SCHEDULING) && defined(HAVE_SCHED_YIELD)
     /* let the other processes die perhaps or whatnot */
     sched_yield ();
@@ -4830,7 +4852,15 @@
     return (0);
 }
 
-/* We respond to fatal errors by restarting the display */
+/* Ignore fatal X errors when user did ctl-alt-backspace */
+static gint
+gdm_slave_ignore_xioerror_handler (Display *disp)
+{
+    gdm_debug ("Fatal X error detected.  Ignoring same during session shutdown.");
+    Longjmp(ignore_xioerror_jmp, 1);
+}
+
+/* We usually respond to fatal errors by restarting the display */
 static gint
 gdm_slave_xioerror_handler (Display *disp)
 {