[PATCH] sc16is7xx: Drop bogus use of IRQF_ONESHOT

From: Julia Cartwright
Date: Mon Oct 03 2016 - 11:15:18 EST

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
queue_kthread_work from sc16is7xx_irq
sc16is7xx_irq [sc16is7xx] from handle_irq_event_percpu
handle_irq_event_percpu from handle_irq_event
handle_irq_event from handle_level_irq
handle_level_irq from generic_handle_irq
generic_handle_irq from mxc_gpio_irq_handler
mxc_gpio_irq_handler from mx3_gpio_irq_handler
mx3_gpio_irq_handler from generic_handle_irq
generic_handle_irq from __handle_domain_irq
__handle_domain_irq from gic_handle_irq
gic_handle_irq from __irq_svc
__irq_svc from rt_spin_unlock
rt_spin_unlock from kthread_worker_fn
kthread_worker_fn from kthread
kthread from ret_from_fork

Fixes: 9e6f4ca3e567 ("sc16is7xx: use kthread_worker for tx_work and irq")
Reported-by: Sean Nyekjaer <sean.nyekjaer@xxxxxxxxx>
Signed-off-by: Josh Cartwright <joshc@xxxxxx>
Cc: linux-rt-users@xxxxxxxxxxxxxxx
Cc: Jakub Kicinski <moorray3@xxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Cc: linux-serial@xxxxxxxxxxxxxxx
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Julia Cartwright <julia@xxxxxx>
This patch has been in -rt for a little while, but it isn't -rt specific.

See relevant bug report thread which starts here:


drivers/tty/serial/sc16is7xx.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index a9d94f7..96a374d 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -1260,7 +1260,7 @@ static int sc16is7xx_probe(struct device *dev,

/* 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;