sfc: pass valid pointers from efx_enqueue_unwind

The bytes_compl and pkts_compl pointers passed to efx_dequeue_buffers
cannot be NULL. Add a paranoid warning to check this condition and fix
the one case where they were NULL.

efx_enqueue_unwind() is called very rarely, during error handling.
Without this fix it would fail with a NULL pointer dereference in
efx_dequeue_buffer, with efx_enqueue_skb in the call stack.

Fixes: e9117e5099ea ("sfc: Firmware-Assisted TSO version 2")
Reported-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Bert Kenward <bkenward@solarflare.com>
Tested-by: Jarod Wilson <jarod@redhat.com>
Acked-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/sfc/tx.c

@@ -77,6 +77,7 @@ static void efx_dequeue_buffer(struct efx_tx_queue *tx_queue,
 	}
 
 	if (buffer->flags & EFX_TX_BUF_SKB) {
+		EFX_WARN_ON_PARANOID(!pkts_compl || !bytes_compl);
 		(*pkts_compl)++;
 		(*bytes_compl) += buffer->skb->len;
 		dev_consume_skb_any((struct sk_buff *)buffer->skb);
@@ -426,12 +427,14 @@ static int efx_tx_map_data(struct efx_tx_queue *tx_queue, struct sk_buff *skb,
 static void efx_enqueue_unwind(struct efx_tx_queue *tx_queue)
 {
 	struct efx_tx_buffer *buffer;
+	unsigned int bytes_compl = 0;
+	unsigned int pkts_compl = 0;
 
 	/* Work backwards until we hit the original insert pointer value */
 	while (tx_queue->insert_count != tx_queue->write_count) {
 		--tx_queue->insert_count;
 		buffer = __efx_tx_queue_get_insert_buffer(tx_queue);
-		efx_dequeue_buffer(tx_queue, buffer, NULL, NULL);
+		efx_dequeue_buffer(tx_queue, buffer, &pkts_compl, &bytes_compl);
 	}
 }