bna: MBOX IRQ Flag Check after Locking

Change details:
 - Check the BNAD_RF_MBOX_IRQ_DISABLED flag after acquiring the bna_lock,
   since checking the flag and executing bna_mbox_handler needs to be atomic.
   If not, it opens up window where flag is reset when it was checked, but got
   set while spinning on the lock by the other thread which is actually
   holding the lock

Signed-off-by: Gurunatha Karaje <gkaraje@brocade.com>
Signed-off-by: Rasesh Mody <rmody@brocade.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/brocade/bna/bnad.c

@@ -586,10 +586,11 @@ bnad_msix_mbox_handler(int irq, void *data)
 	unsigned long flags;
 	struct bnad *bnad = (struct bnad *)data;
 
-	if (unlikely(test_bit(BNAD_RF_MBOX_IRQ_DISABLED, &bnad->run_flags)))
-		return IRQ_HANDLED;
-
 	spin_lock_irqsave(&bnad->bna_lock, flags);
+	if (unlikely(test_bit(BNAD_RF_MBOX_IRQ_DISABLED, &bnad->run_flags))) {
+		spin_unlock_irqrestore(&bnad->bna_lock, flags);
+		return IRQ_HANDLED;
+	}
 
 	bna_intr_status_get(&bnad->bna, intr_status);
 
@@ -612,15 +613,18 @@ bnad_isr(int irq, void *data)
 	struct bnad_rx_ctrl *rx_ctrl;
 	struct bna_tcb *tcb = NULL;
 
-	if (unlikely(test_bit(BNAD_RF_MBOX_IRQ_DISABLED, &bnad->run_flags)))
+	spin_lock_irqsave(&bnad->bna_lock, flags);
+	if (unlikely(test_bit(BNAD_RF_MBOX_IRQ_DISABLED, &bnad->run_flags))) {
+		spin_unlock_irqrestore(&bnad->bna_lock, flags);
 		return IRQ_NONE;
+	}
 
 	bna_intr_status_get(&bnad->bna, intr_status);
 
-	if (unlikely(!intr_status))
+	if (unlikely(!intr_status)) {
+		spin_unlock_irqrestore(&bnad->bna_lock, flags);
 		return IRQ_NONE;
-
-	spin_lock_irqsave(&bnad->bna_lock, flags);
+	}
 
 	if (BNA_IS_MBOX_ERR_INTR(&bnad->bna, intr_status))
 		bna_mbox_handler(&bnad->bna, intr_status);