printk: Update the printk series.

This is an all-in-one update of the printk series. It updates from the
previous version to the current development version which is under
discussion plus the PREEMPT_RT bits for the atomic console.

This updates the atomic console plus addresses some issues raised by the kernel
robot.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

drivers/tty/serial/8250/8250_port.c

@@ -3498,10 +3498,6 @@ bool serial8250_console_write_atomic(struct uart_8250_port *up,
 	if (up->em485)
 		return false;
 
-	/* Atomic console does not support handling modem control. */
-	if (up->msr_saved_flags)
-		return false;
-
 	touch_nmi_watchdog();
 
 	if (!nbcon_enter_unsafe(wctxt))

kernel/printk/printk.c

@@ -282,6 +282,7 @@ EXPORT_SYMBOL(console_list_unlock);
  * Return: A cookie to pass to console_srcu_read_unlock().
  */
 int console_srcu_read_lock(void)
+	__acquires(&console_srcu)
 {
 	return srcu_read_lock_nmisafe(&console_srcu);
 }
@@ -295,6 +296,7 @@ EXPORT_SYMBOL(console_srcu_read_lock);
  * Counterpart to console_srcu_read_lock()
  */
 void console_srcu_read_unlock(int cookie)
+	__releases(&console_srcu)
 {
 	srcu_read_unlock_nmisafe(&console_srcu, cookie);
 }
@@ -459,7 +461,7 @@ static int __read_mostly suppress_panic_printk;
 
 DECLARE_WAIT_QUEUE_HEAD(log_wait);
 
-DECLARE_WAIT_QUEUE_HEAD(legacy_wait);
+static DECLARE_WAIT_QUEUE_HEAD(legacy_wait);
 
 /* All 3 protected by @syslog_lock. */
 /* the next printk record to read by syslog(READ) or /proc/kmsg */