netconsole: avoid CON_ENABLED misuse to track registration

The CON_ENABLED flag is being misused to track whether or not the
extended console should be or has been registered. Instead use
a local variable to decide if the extended console should be
registered and console_is_registered() to determine if it has
been registered.

Also add a check in cleanup_netconsole() to only unregister the
extended console if it has been registered.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20221116162152.193147-32-john.ogness@linutronix.de

drivers/net/netconsole.c

@@ -332,10 +332,8 @@ static ssize_t enabled_store(struct config_item *item,
 	}
 
 	if (enabled) {	/* true */
-		if (nt->extended && !(netconsole_ext.flags & CON_ENABLED)) {
-			netconsole_ext.flags |= CON_ENABLED;
+		if (nt->extended && !console_is_registered(&netconsole_ext))
 			register_console(&netconsole_ext);
-		}
 
 		/*
 		 * Skip netpoll_parse_options() -- all the attributes are
@@ -869,7 +867,7 @@ static void write_msg(struct console *con, const char *msg, unsigned int len)
 
 static struct console netconsole_ext = {
 	.name	= "netcon_ext",
-	.flags	= CON_EXTENDED,	/* starts disabled, registered on first use */
+	.flags	= CON_ENABLED | CON_EXTENDED,
 	.write	= write_ext_msg,
 };
 
@@ -883,6 +881,7 @@ static int __init init_netconsole(void)
 {
 	int err;
 	struct netconsole_target *nt, *tmp;
+	bool extended = false;
 	unsigned long flags;
 	char *target_config;
 	char *input = config;
@@ -895,11 +894,12 @@ static int __init init_netconsole(void)
 				goto fail;
 			}
 			/* Dump existing printks when we register */
-			if (nt->extended)
-				netconsole_ext.flags |= CON_PRINTBUFFER |
-							CON_ENABLED;
-			else
+			if (nt->extended) {
+				extended = true;
+				netconsole_ext.flags |= CON_PRINTBUFFER;
+			} else {
 				netconsole.flags |= CON_PRINTBUFFER;
+			}
 
 			spin_lock_irqsave(&target_list_lock, flags);
 			list_add(&nt->list, &target_list);
@@ -915,7 +915,7 @@ static int __init init_netconsole(void)
 	if (err)
 		goto undonotifier;
 
-	if (netconsole_ext.flags & CON_ENABLED)
+	if (extended)
 		register_console(&netconsole_ext);
 	register_console(&netconsole);
 	pr_info("network logging started\n");
@@ -945,6 +945,7 @@ static void __exit cleanup_netconsole(void)
 {
 	struct netconsole_target *nt, *tmp;
 
+	if (console_is_registered(&netconsole_ext))
 		unregister_console(&netconsole_ext);
 	unregister_console(&netconsole);
 	dynamic_netconsole_exit();