e1000: Avoid unhandled IRQ

If hardware asserted an interrupt and driver is down,
then there is nothing to do so return IRQ_HANDLED
instead of IRQ_NONE. Returning IRQ_NONE in above
situation causes screaming IRQ on virtual machines.

CC: Andy Gospodarek <gospo@redhat.com>
Signed-off-by: Tushar Dave <tushar.n.dave@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/e1000/e1000_main.c

@@ -3478,9 +3478,17 @@ static irqreturn_t e1000_intr(int irq, void *data)
 	struct e1000_hw *hw = &adapter->hw;
 	u32 icr = er32(ICR);
 
-	if (unlikely((!icr) || test_bit(__E1000_DOWN, &adapter->flags)))
+	if (unlikely((!icr)))
 		return IRQ_NONE;  /* Not our interrupt */
 
+	/*
+	 * we might have caused the interrupt, but the above
+	 * read cleared it, and just in case the driver is
+	 * down there is nothing to do so return handled
+	 */
+	if (unlikely(test_bit(__E1000_DOWN, &adapter->flags)))
+		return IRQ_HANDLED;
+
 	if (unlikely(icr & (E1000_ICR_RXSEQ | E1000_ICR_LSC))) {
 		hw->get_link_status = 1;
 		/* guard against interrupt when we're going down */