From: Ingo Molnar Date: Fri, 3 Jul 2009 08:30:01 -0500 Subject: [PATCH] serial: 8250: Clean up the locking for -rt Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/3.14/patches-3.14.0-rt1.tar.xz In -RT the spin_lock_irqsave() does not spin but sleep if the lock is taken. Before that, local_irq_save() is invoked which disables interrupts even on -RT. Therefore local_irq_save() + spin_lock() does not work. In the ->sysrq and oops_in_progress case it is save to trylock the lock i.e. this is what we do now anyway except for ->sysrq where we assume that the lock is already taken. The spin_lock_irqsave() grabs the lock and disables the interrupts on vanilla (the same behavior) and on -RT it won't disable interrupts. Signed-off-by: Ingo Molnar Signed-off-by: Thomas Gleixner [bigeasy: add a patch description] Signed-off-by: Sebastian Andrzej Siewior --- drivers/tty/serial/8250/8250_core.c | 15 +++++---------- 1 file changed, 5 insertions(+), 10 deletions(-) --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -2882,14 +2882,10 @@ serial8250_console_write(struct console touch_nmi_watchdog(); - local_irq_save(flags); - if (port->sysrq) { - /* serial8250_handle_irq() already took the lock */ - locked = 0; - } else if (oops_in_progress) { - locked = spin_trylock(&port->lock); - } else - spin_lock(&port->lock); + if (port->sysrq || oops_in_progress) + locked = spin_trylock_irqsave(&port->lock, flags); + else + spin_lock_irqsave(&port->lock, flags); /* * First save the IER then disable the interrupts @@ -2921,8 +2917,7 @@ serial8250_console_write(struct console serial8250_modem_status(up); if (locked) - spin_unlock(&port->lock); - local_irq_restore(flags); + spin_unlock_irqrestore(&port->lock, flags); } static int __init serial8250_console_setup(struct console *co, char *options)