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

From: Sebastian Andrzej Siewior
Date: Fri Mar 11 2016 - 13:05:11 EST

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@xxxxxxxxxxxxx>
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,


- 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);
spin_lock_irqsave(&port->lock, flags);