Subject: drivers-tty-pl011-irq-disable-madness.patch From: Thomas Gleixner Date: Tue, 08 Jan 2013 21:36:51 +0100 Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/3.14/patches-3.14.0-rt1.tar.xz Signed-off-by: Thomas Gleixner --- drivers/tty/serial/amba-pl011.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) --- a/drivers/tty/serial/amba-pl011.c +++ b/drivers/tty/serial/amba-pl011.c @@ -1919,13 +1919,19 @@ pl011_console_write(struct console *co, clk_enable(uap->clk); - local_irq_save(flags); + /* + * local_irq_save(flags); + * + * This local_irq_save() is nonsense. If we come in via sysrq + * handling then interrupts are already disabled. Aside of + * that the port.sysrq check is racy on SMP regardless. + */ if (uap->port.sysrq) locked = 0; else if (oops_in_progress) - locked = spin_trylock(&uap->port.lock); + locked = spin_trylock_irqsave(&uap->port.lock, flags); else - spin_lock(&uap->port.lock); + spin_lock_irqsave(&uap->port.lock, flags); /* * First save the CR then disable the interrupts @@ -1947,8 +1953,7 @@ pl011_console_write(struct console *co, writew(old_cr, uap->port.membase + UART011_CR); if (locked) - spin_unlock(&uap->port.lock); - local_irq_restore(flags); + spin_unlock_irqrestore(&uap->port.lock, flags); clk_disable(uap->clk); }