linux-kernel - [RFC RT] tty: serial: 8250: don't take the lock on OOPs

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Message-ID: <20160311180504.GB29850@linutronix.de>
Date:	Fri, 11 Mar 2016 19:05:04 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	tglx@...utronix.de, rostedt@...dmis.org
Cc:	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: [RFC RT] tty: serial: 8250: don't take the lock on OOPs

On panic() from IRQ (for instance from the lockup detector) we will
end up in an endless loop on -RT. Each time we invoke
spin_trylock_irqsave() we will trigger the WARN_ON() in rt_mutex_trylock().
The WARN_ON() will stuff more data into the printk buffer than we can
print on one iteration and so we never end the printing loop.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 drivers/tty/serial/8250/8250_port.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 5568d70eee0c..138b1b985063 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -2850,9 +2850,9 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s,
 
 	serial8250_rpm_get(up);
 
-	if (port->sysrq)
+	if (port->sysrq || oops_in_progress)
 		locked = 0;
-	else if (oops_in_progress || in_kdb_printk())
+	else if (in_kdb_printk())
 		locked = spin_trylock_irqsave(&port->lock, flags);
 	else
 		spin_lock_irqsave(&port->lock, flags);
-- 
2.7.0