genirq: Handle force threading of irqs with primary and thread handler

Force threading of interrupts does not really deal with interrupts
which are requested with a primary and a threaded handler. The current
policy is to leave them alone and let the primary handler run in
interrupt context, but we set the ONESHOT flag for those interrupts as
well.

Kohji Okuno debugged a problem with the SDHCI driver where the
interrupt thread waits for a hardware interrupt to trigger, which can't
work well because the hardware interrupt is masked due to the ONESHOT
flag being set. He proposed to set the ONESHOT flag only if the
interrupt does not provide a thread handler.

Though that does not work either because these interrupts can be
shared. So the other interrupt would rightfully get the ONESHOT flag
set and therefor the same situation would happen again.

To deal with this proper, we need to force thread the primary handler
of such interrupts as well. That means that the primary interrupt
handler is treated as any other primary interrupt handler which is not
marked IRQF_NO_THREAD. The threaded handler becomes a separate thread
so the SDHCI flow logic can be handled gracefully.

The same issue was reported against 4.1-rt.

Reported-and-tested-by: Kohji Okuno <okuno.kohji@jp.panasonic.com>
Reported-By: Michal Smucr <msmucr@gmail.com>
Reported-and-tested-by: Nathan Sullivan <nathan.sullivan@ni.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1509211058080.5606@nanos
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index be7e75c945e9..ad16809c8596 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -102,6 +102,7 @@ typedef irqreturn_t (*irq_handler_t)(int, void *);
  * @flags:	flags (see IRQF_* above)
  * @thread_fn:	interrupt handler function for threaded interrupts
  * @thread:	thread pointer for threaded interrupts
+ * @secondary:	pointer to secondary irqaction (force threading)
  * @thread_flags:	flags related to @thread
  * @thread_mask:	bitmask for keeping track of @thread activity
  * @dir:	pointer to the proc/irq/NN/name entry
@@ -113,6 +114,7 @@ struct irqaction {
 	struct irqaction	*next;
 	irq_handler_t		thread_fn;
 	struct task_struct	*thread;
+	struct irqaction	*secondary;
 	unsigned int		irq;
 	unsigned int		flags;
 	unsigned long		thread_flags;