genirq: Warn when IRQ_NOAUTOEN is used with shared interrupts

Shared interrupts do not go well with disabling auto enable:

1) The sharing interrupt might request it while it's still disabled and
   then wait for interrupts forever.

2) The interrupt might have been requested by the driver sharing the line
   before IRQ_NOAUTOEN has been set. So the driver which expects that
   disabled state after calling request_irq() will not get what it wants.
   Even worse, when it calls enable_irq() later, it will trigger the
   unbalanced enable_irq() warning.
Reported-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: dianders@chromium.org
Cc: jeffy <jeffy.chen@rock-chips.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: tfiga@chromium.org
Link: http://lkml.kernel.org/r/20170531100212.210682135@linutronix.de

kernel/irq/chip.c

@@ -935,6 +935,13 @@ void irq_modify_status(unsigned int irq, unsigned long clr, unsigned long set)
 
 	if (!desc)
 		return;
+
+	/*
+	 * Warn when a driver sets the no autoenable flag on an already
+	 * active interrupt.
+	 */
+	WARN_ON_ONCE(!desc->depth && (set & _IRQ_NOAUTOEN));
+
 	irq_settings_clr_and_set(desc, clr, set);
 
 	irqd_clear(&desc->irq_data, IRQD_NO_BALANCING | IRQD_PER_CPU |

kernel/irq/manage.c

@@ -1334,11 +1334,19 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
 		if (new->flags & IRQF_ONESHOT)
 			desc->istate |= IRQS_ONESHOT;
 
-		if (irq_settings_can_autoenable(desc))
+		if (irq_settings_can_autoenable(desc)) {
 			irq_startup(desc, true);
-		else
+		} else {
+			/*
+			 * Shared interrupts do not go well with disabling
+			 * auto enable. The sharing interrupt might request
+			 * it while it's still disabled and then wait for
+			 * interrupts forever.
+			 */
+			WARN_ON_ONCE(new->flags & IRQF_SHARED);
 			/* Undo nested disables: */
 			desc->depth = 1;
+		}
 
 		/* Exclude IRQ from balancing if requested */
 		if (new->flags & IRQF_NOBALANCING) {