From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Mon, 11 Apr 2016 16:55:02 +0200
Subject: tty: serial: 8250: don't take the trylock during oops
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: 4326f950cf809b30e4cf840333a262578281c3e8
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

An oops with irqs off (panic() from irqsafe hrtimer like the watchdog
timer) will lead to a lockdep warning on each invocation and as such
never completes.
Therefore we skip the trylock in the oops case.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 drivers/tty/serial/8250/8250_port.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -3179,10 +3179,8 @@ void serial8250_console_write(struct uar
 
 	serial8250_rpm_get(up);
 
-	if (port->sysrq)
+	if (port->sysrq || oops_in_progress)
 		locked = 0;
-	else if (oops_in_progress)
-		locked = spin_trylock_irqsave(&port->lock, flags);
 	else
 		spin_lock_irqsave(&port->lock, flags);