printk: do not wait for consoles when suspended

The console_stop() and console_start() functions call pr_flush().
When suspending, these functions are called by the serial subsystem
while the serial port is suspended. In this scenario, if there are
any pending messages, a call to pr_flush() will always result in a
timeout because the serial port cannot make forward progress. This
causes longer suspend and resume times.

Add a check in pr_flush() so that it will immediately timeout if
the consoles are suspended.

Fixes: 3b604ca8 ("printk: add pr_flush()")
Reported-by: Todd Brandt <todd.e.brandt@linux.intel.com>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Tested-by: Todd Brandt <todd.e.brandt@linux.intel.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220715061042.373640-2-john.ogness@linutronix.de

kernel/printk/printk.c

@@ -3380,6 +3380,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
 		diff = 0;
 
 		console_lock();
+
 		for_each_console(c) {
 			if (con && con != c)
 				continue;
@@ -3389,11 +3390,19 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
 			if (printk_seq < seq)
 				diff += seq - printk_seq;
 		}
-		console_unlock();
 
-		if (diff != last_diff && reset_on_progress)
+		/*
+		 * If consoles are suspended, it cannot be expected that they
+		 * make forward progress, so timeout immediately. @diff is
+		 * still used to return a valid flush status.
+		 */
+		if (console_suspended)
+			remaining = 0;
+		else if (diff != last_diff && reset_on_progress)
 			remaining = timeout_ms;
 
+		console_unlock();
+
 		if (diff == 0 || remaining == 0)
 			break;