gpio: pca953x: Survive spurious interrupts

The pca953x driver never checks the result of irq_find_mapping(),
which returns 0 when no mapping is found. When a spurious interrupt
is delivered (which can happen under obscure circumstances), the
kernel explodes as it still tries to handle the error code as
a real interrupt.

Handle this particular case and warn on spurious interrupts.
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201005140217.1390851-1-maz@kernel.orgSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-pca953x.c

@@ -824,8 +824,21 @@ static irqreturn_t pca953x_irq_handler(int irq, void *devid)
 	ret = pca953x_irq_pending(chip, pending);
 	mutex_unlock(&chip->i2c_lock);
 
-	for_each_set_bit(level, pending, gc->ngpio)
-		handle_nested_irq(irq_find_mapping(gc->irq.domain, level));
+	if (ret) {
+		ret = 0;
+
+		for_each_set_bit(level, pending, gc->ngpio) {
+			int nested_irq = irq_find_mapping(gc->irq.domain, level);
+
+			if (unlikely(nested_irq <= 0)) {
+				dev_warn_ratelimited(gc->parent, "unmapped interrupt %d\n", level);
+				continue;
+			}
+
+			handle_nested_irq(nested_irq);
+			ret = 1;
+		}
+	}
 
 	return IRQ_RETVAL(ret);
 }