Subject: sc16is7xx: Drop bogus use of IRQF_ONESHOT
From: Josh Cartwright <joshc@ni.com>
Date: Thu, 18 Feb 2016 11:26:12 -0600
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.6/older/patches-4.6.2-rt5.tar.xz

The use of IRQF_ONESHOT when registering an interrupt handler with
request_irq() is non-sensical.

Not only that, it also prevents the handler from being threaded when it
otherwise should be w/ IRQ_FORCED_THREADING is enabled.  This causes the
following deadlock observed by Sean Nyekjaer on -rt:

Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
[..]
   rt_spin_lock_slowlock from (queue_kthread_work+0x18/0x74)
   queue_kthread_work) from (sc16is7xx_irq+0x10/0x18 [sc16is7xx])
   sc16is7xx_irq [sc16is7xx]) from (handle_irq_event_percpu+0x70/0x158)
   handle_irq_event_percpu) from (handle_irq_event+0x68/0xa8)
   handle_irq_event) from (handle_level_irq+0x10c/0x184)
   handle_level_irq) from (generic_handle_irq+0x2c/0x3c)
   generic_handle_irq) from (mxc_gpio_irq_handler+0x3c/0x108)
   mxc_gpio_irq_handler) from (mx3_gpio_irq_handler+0x80/0xcc)
   mx3_gpio_irq_handler) from (generic_handle_irq+0x2c/0x3c)
   generic_handle_irq) from (__handle_domain_irq+0x7c/0xe8)
   __handle_domain_irq) from (gic_handle_irq+0x24/0x5c)
   gic_handle_irq) from (__irq_svc+0x40/0x88)
   (__irq_svc) from (rt_spin_unlock+0x1c/0x68)
   (rt_spin_unlock) from (kthread_worker_fn+0x104/0x17c)
   (kthread_worker_fn) from (kthread+0xd0/0xe8)
   (kthread) from (ret_from_fork+0x14/0x2c)

Fixes: 9e6f4ca3e567 ("sc16is7xx: use kthread_worker for tx_work and irq")
Reported-by: Sean Nyekjaer <sean.nyekjaer@prevas.dk>
Signed-off-by: Josh Cartwright <joshc@ni.com>
Cc: linux-rt-users@vger.kernel.org
Cc: Jakub Kicinski <moorray3@wp.pl>
Cc: stable@vger.kernel.org
Cc: linux-serial@vger.kernel.org
Link: http://lkml.kernel.org/r/1455816372-13989-1-git-send-email-joshc@ni.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 drivers/tty/serial/sc16is7xx.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -1251,7 +1251,7 @@ static int sc16is7xx_probe(struct device
 
 	/* Setup interrupt */
 	ret = devm_request_irq(dev, irq, sc16is7xx_irq,
-			       IRQF_ONESHOT | flags, dev_name(dev), s);
+			       flags, dev_name(dev), s);
 	if (!ret)
 		return 0;
 
