From: Thomas Gleixner Date: Tue, 8 Jan 2013 21:36:51 +0100 Subject: [PATCH 165/353] tty/serial/pl011: Make the locking work on RT Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=0078406dbe103225ceb07433c4d141a02e66e775 The lock is a sleeping lock and local_irq_save() is not the optimsation we are looking for. Redo it to make it work on -RT and non-RT. Signed-off-by: Thomas Gleixner --- drivers/tty/serial/amba-pl011.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c index d1f4882d9f40..2773d08e1d4a 100644 --- a/drivers/tty/serial/amba-pl011.c +++ b/drivers/tty/serial/amba-pl011.c @@ -2227,13 +2227,19 @@ pl011_console_write(struct console *co, const char *s, unsigned int count) 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 @@ -2259,8 +2265,7 @@ pl011_console_write(struct console *co, const char *s, unsigned int count) pl011_write(old_cr, uap, REG_CR); if (locked) - spin_unlock(&uap->port.lock); - local_irq_restore(flags); + spin_unlock_irqrestore(&uap->port.lock, flags); clk_disable(uap->clk); }