MFC svn 267065 and 267187

make sure ifp->if_transmit returns 0 if a buffer is enqueued.
This should also be merged to stable/9.

After this fix, drivers still known to have this bug are igxbe/ixv
and i40e.

Drivers using if_transmit are correct, and so are most of the
other drivers that reassing if_transmit.

Among other things, this bug causes panics when using netmap emulation
on top of generic drivers.

4 files changed, 6 insertions, 8 deletions

diff --git a/sys/dev/e1000/if_igb.c b/sys/dev/e1000/if_igb.c
index 3b6af17..15d71ce 100644
--- a/sys/dev/e1000/if_igb.c
+++ b/sys/dev/e1000/if_igb.c
@@ -988,12 +988,12 @@ igb_mq_start(struct ifnet *ifp, struct mbuf *m)
 	if (err)
 		return (err);
 	if (IGB_TX_TRYLOCK(txr)) {
-		err = igb_mq_start_locked(ifp, txr);
+		igb_mq_start_locked(ifp, txr);
 		IGB_TX_UNLOCK(txr);
 	} else
 		taskqueue_enqueue(que->tq, &txr->txq_task);
 
-	return (err);
+	return (0);
 }
 
 static int
diff --git a/sys/dev/ixgbe/ixgbe.c b/sys/dev/ixgbe/ixgbe.c
index 5b9fa01..597256a 100644
--- a/sys/dev/ixgbe/ixgbe.c
+++ b/sys/dev/ixgbe/ixgbe.c
@@ -831,12 +831,12 @@ ixgbe_mq_start(struct ifnet *ifp, struct mbuf *m)
 	if (err)
 		return (err);
 	if (IXGBE_TX_TRYLOCK(txr)) {
-		err = ixgbe_mq_start_locked(ifp, txr);
+		ixgbe_mq_start_locked(ifp, txr);
 		IXGBE_TX_UNLOCK(txr);
 	} else
 		taskqueue_enqueue(que->tq, &txr->txq_task);
 
-	return (err);
+	return (0);
 }
 
 static int
diff --git a/sys/dev/virtio/network/if_vtnet.c b/sys/dev/virtio/network/if_vtnet.c
index 055a2e3..9e1ad26 100644
--- a/sys/dev/virtio/network/if_vtnet.c
+++ b/sys/dev/virtio/network/if_vtnet.c
@@ -2260,7 +2260,6 @@ vtnet_txq_mq_start_locked(struct vtnet_txq *txq, struct mbuf *m)
 	while ((m = drbr_peek(ifp, br)) != NULL) {
 		if (virtqueue_full(vq)) {
 			drbr_putback(ifp, br, m);
-			error = ENOBUFS;
 			break;
 		}
 
@@ -2283,7 +2282,7 @@ vtnet_txq_mq_start_locked(struct vtnet_txq *txq, struct mbuf *m)
 		txq->vtntx_watchdog = VTNET_TX_TIMEOUT;
 	}
 
-	return (error);
+	return (0);
 }
 
 static int
diff --git a/sys/dev/vmware/vmxnet3/if_vmx.c b/sys/dev/vmware/vmxnet3/if_vmx.c
index 3acc672..e8d213e 100644
--- a/sys/dev/vmware/vmxnet3/if_vmx.c
+++ b/sys/dev/vmware/vmxnet3/if_vmx.c
@@ -2933,7 +2933,6 @@ vmxnet3_txq_mq_start_locked(struct vmxnet3_txqueue *txq, struct mbuf *m)
 		/* Assume worse case if this mbuf is the head of a chain. */
 		if (m->m_next != NULL && avail < VMXNET3_TX_MAXSEGS) {
 			drbr_putback(ifp, br, m);
-			error = ENOBUFS;
 			break;
 		}
 
@@ -2956,7 +2955,7 @@ vmxnet3_txq_mq_start_locked(struct vmxnet3_txqueue *txq, struct mbuf *m)
 		txq->vxtxq_watchdog = VMXNET3_WATCHDOG_TIMEOUT;
 	}
 
-	return (error);
+	return (0);
 }
 
 static int