printk: Flush console on unregister_console()

Ensure consoles have flushed pending records before
unregistering. The console should print up to at least its
related "console disabled" record.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20240904120536.115780-4-john.ogness@linutronix.deSigned-off-by: Petr Mladek <pmladek@suse.com>

kernel/printk/printk.c

@@ -3771,11 +3771,16 @@ static int unregister_console_locked(struct console *console)
 	if (res > 0)
 		return 0;
 
+	if (!console_is_registered_locked(console))
+		res = -ENODEV;
+	else if (console_is_usable(console, console->flags))
+		__pr_flush(console, 1000, true);
+
 	/* Disable it unconditionally */
 	console_srcu_write_flags(console, console->flags & ~CON_ENABLED);
 
-	if (!console_is_registered_locked(console))
-		return -ENODEV;
+	if (res < 0)
+		return res;
 
 	/*
 	 * Use the driver synchronization to ensure that the hardware is not