genirq: Use the correct variable for note_interrupt

note_interrupt wants to be called with the combined result of all
handlers called, not with the last one. If it's a shared interrupt
then the last handler might return IRQ_NONE often enough to trigger
the spurious dectector which turns off a perfectly fine working
interrupt line. Bug was introduced in commit 1277a532(genirq: Simplify
handle_irq_event()).

Yes, I really messed up there. First the variable ret should not have
been named differently to avoid similarity with retval. Second it
should have been declared in the do {} loop.

Rename it to res and move it into the do {} loop and vanish under a
huge brown paperbag.
Reported-bisected-tested-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/irq/handle.c

@@ -54,24 +54,26 @@ static void warn_no_thread(unsigned int irq, struct irqaction *action)
 irqreturn_t
 handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action)
 {
-	irqreturn_t ret, retval = IRQ_NONE;
+	irqreturn_t retval = IRQ_NONE;
 	unsigned int random = 0, irq = desc->irq_data.irq;
 
 	do {
+		irqreturn_t res;
+
 		trace_irq_handler_entry(irq, action);
-		ret = action->handler(irq, action->dev_id);
-		trace_irq_handler_exit(irq, action, ret);
+		res = action->handler(irq, action->dev_id);
+		trace_irq_handler_exit(irq, action, res);
 
 		if (WARN_ON_ONCE(!irqs_disabled()))
 			local_irq_disable();
 
-		switch (ret) {
+		switch (res) {
 		case IRQ_WAKE_THREAD:
 			/*
 			 * Set result to handled so the spurious check
 			 * does not trigger.
 			 */
-			ret = IRQ_HANDLED;
+			res = IRQ_HANDLED;
 
 			/*
 			 * Catch drivers which return WAKE_THREAD but
@@ -105,7 +107,7 @@ handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action)
 			break;
 		}
 
-		retval |= ret;
+		retval |= res;
 		action = action->next;
 	} while (action);
 
@@ -113,7 +115,7 @@ handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action)
 		add_interrupt_randomness(irq);
 
 	if (!noirqdebug)
-		note_interrupt(irq, desc, ret);
+		note_interrupt(irq, desc, retval);
 	return retval;
 }