[PATCH] Close race with fbcon notifer

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

diff -urN fbdev-2.5/drivers/video/console/fbcon.c linuxppc-2.5-benh/drivers/video/console/fbcon.c
--- fbdev-2.5/drivers/video/console/fbcon.c	2004-02-09 14:48:31.000000000 +1100
+++ linuxppc-2.5-benh/drivers/video/console/fbcon.c	2004-02-10 15:21:29.754526880 +1100
@@ -602,7 +602,6 @@
 
 	/* on which frame buffer will we open this console? */
 	info = registered_fb[(int) con2fb_map[unit]];
-	
 	if (info->var.accel_flags)
 		fb_display[unit].scrollmode = SCROLL_YNOMOVE;
 	else
@@ -2255,16 +2254,24 @@
 
 static void fbcon_resumed(struct fb_info *info)
 {
-	struct vc_data *vc = vc_cons[info->currcon].d;
+	struct vc_data *vc;
+
+	if (info->currcon < 0)
+		return;
+	vc = vc_cons[info->currcon].d;
 
 	update_screen(vc->vc_num);
 }
 
 static void fbcon_mode_changed(struct fb_info *info)
 {
-	struct vc_data *vc = vc_cons[info->currcon].d;
+	struct vc_data *vc;
 	int rows, cols;
 
+	if (info->currcon < 0)
+		return;
+	vc = vc_cons[info->currcon].d;
+
 	/* This isn't perfect yet. If we change one console, we
 	 * don't change them all and we switch back to the wrong
 	 * mode on next console switch. We need to either keep a
@@ -2339,6 +2346,7 @@
 	.notifier_call	= fbcon_event_notify,
 };
 
+static int fbcon_event_notifier_registered;
 
 int __init fb_console_init(void)
 {
@@ -2349,14 +2357,24 @@
 	take_over_console(&fb_con, first_fb_vc, last_fb_vc, fbcon_is_default);
 	info = registered_fb[num_registered_fb-1];	
 
-	fb_register_client(&fbcon_event_notifer);
+	acquire_console_semaphore();
+	if (!fbcon_event_notifier_registered) {
+		fb_register_client(&fbcon_event_notifer);
+		fbcon_event_notifier_registered = 1;
+	} 
+	release_console_semaphore();
 
 	return 0;
 }
 
 void __exit fb_console_exit(void)
 {
-	fb_unregister_client(&fbcon_event_notifer);
+	acquire_console_semaphore();
+	if (fbcon_event_notifier_registered) {
+		fb_unregister_client(&fbcon_event_notifer);
+		fbcon_event_notifier_registered = 0;
+	}
+	release_console_semaphore();
 	give_up_console(&fb_con);
 }	
 




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