Fix reentrancy problem/crash in xterm.c

* src/xterm.c (x_ignore_errors_for_next_request)
(x_stop_ignoring_errors): Be paranoid and block input inside the
protected section.
(x_focus_frame): Block input around critical section.

src/xterm.c

@@ -25461,6 +25461,17 @@ x_clean_failable_requests (struct x_display_info *dpyinfo)
 				    + (last - first));
 }
 
+/* Protect a section of X requests: ignore errors generated by X
+   requests made from now until `x_stop_ignoring_errors'.  Each call
+   must be paired with a call to `x_stop_ignoring_errors', and
+   recursive calls inside the protected section are not allowed.
+
+   The advantage over x_catch_errors followed by
+   x_uncatch_errors_after_check is that this function does not sync to
+   catch errors if requests were made.  It should be used instead of
+   those two functions for catching errors around requests that do not
+   require a reply.  */
+
 void
 x_ignore_errors_for_next_request (struct x_display_info *dpyinfo)
 {
@@ -25468,7 +25479,13 @@ x_ignore_errors_for_next_request (struct x_display_info *dpyinfo)
   unsigned long next_request;
 #ifdef HAVE_GTK3
   GdkDisplay *gdpy;
+#endif
 
+  /* This code is not reentrant, so be sure nothing calls it
+     recursively in response to input.  */
+  block_input ();
+
+#ifdef HAVE_GTK3
   /* GTK 3 tends to override our own error handler inside certain
      callbacks, which this can be called from.  Instead of trying to
      restore our own, add a trap for the following requests with
@@ -25537,6 +25554,8 @@ x_stop_ignoring_errors (struct x_display_info *dpyinfo)
   if (gdpy)
     gdk_x11_display_error_trap_pop_ignored (gdpy);
 #endif
+
+  unblock_input ();
 }
 
 /* Undo the last x_catch_errors call.
@@ -27836,6 +27855,10 @@ x_focus_frame (struct frame *f, bool noactivate)
   struct x_display_info *dpyinfo;
   Time time;
 
+  /* The code below is not reentrant wrt to dpyinfo->x_focus_frame and
+     friends being set.  */
+  block_input ();
+
   dpyinfo = FRAME_DISPLAY_INFO (f);
 
   if (FRAME_X_EMBEDDED_P (f))
@@ -27866,7 +27889,7 @@ x_focus_frame (struct frame *f, bool noactivate)
 	     the current workspace, and mapping it, etc, before moving
 	     input focus to the frame.  */
 	  x_ewmh_activate_frame (f);
-	  return;
+	  goto out;
 	}
 
       if (NILP (Vx_no_window_manager))
@@ -27900,6 +27923,9 @@ x_focus_frame (struct frame *f, bool noactivate)
 			      matter.  */
 			   CurrentTime);
     }
+
+ out:
+  unblock_input ();
 }