ibm emac: Fix locking for enable/disable eob irq

Calls to mal_enable_eob_irq perform a read-write-modify of a dcr to
enable device irqs which is protected by a spin lock. However calls to
mal_disable_eob_irq do not take the corresponding lock.

This patch resolves the problem by ensuring that calls to
mal_disable_eob_irq also take the lock.
Signed-off-by: Alistair Popple <alistair@popple.id.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/ibm/emac/mal.c

@@ -263,7 +263,9 @@ static inline void mal_schedule_poll(struct mal_instance *mal)
 {
 	if (likely(napi_schedule_prep(&mal->napi))) {
 		MAL_DBG2(mal, "schedule_poll" NL);
+		spin_lock(&mal->lock);
 		mal_disable_eob_irq(mal);
+		spin_unlock(&mal->lock);
 		__napi_schedule(&mal->napi);
 	} else
 		MAL_DBG2(mal, "already in poll" NL);
@@ -445,7 +447,9 @@ static int mal_poll(struct napi_struct *napi, int budget)
 			if (!napi_reschedule(napi))
 				goto more_work;
 
+			spin_lock_irqsave(&mal->lock, flags);
 			mal_disable_eob_irq(mal);
+			spin_unlock_irqrestore(&mal->lock, flags);
 			goto again;
 		}
 		mc->ops->poll_tx(mc->dev);