Prepending an mbuf after loading a DMA map results in unexpected

result. So, modify mbuf chains before loading a DMA map.

1 files changed, 28 insertions, 31 deletions

diff --git a/sys/dev/em/if_em.c b/sys/dev/em/if_em.c
index 02494b5..cd6d716 100644
--- a/sys/dev/em/if_em.c
+++ b/sys/dev/em/if_em.c
@@ -1412,31 +1412,6 @@ em_encap(struct em_softc *sc, struct mbuf **m_headp)
 		}
 	}
 
-	/*
-	 * Map the packet for DMA.
-	 */
-	tx_buffer = &sc->tx_buffer_area[sc->next_avail_tx_desc];
-	tx_buffer_last = tx_buffer;
-	map = tx_buffer->map;
-	error = bus_dmamap_load_mbuf_sg(sc->txtag, map, m_head, segs, &nsegs,
-	    BUS_DMA_NOWAIT);
-	if (error != 0) {
-		sc->no_tx_dma_setup++;
-		return (error);
-	}
-	KASSERT(nsegs != 0, ("em_encap: empty packet"));
-
-	if (nsegs > sc->num_tx_desc_avail) {
-		sc->no_tx_desc_avail2++;
-		error = ENOBUFS;
-		goto encap_fail;
-	}
-
-	if (ifp->if_hwassist > 0)
-		em_transmit_checksum_setup(sc,  m_head, &txd_upper, &txd_lower);
-	else
-		txd_upper = txd_lower = 0;
-
 	/* Find out if we are in vlan mode. */
 	mtag = VLAN_OUTPUT_TAG(ifp, m_head);
 
@@ -1453,21 +1428,18 @@ em_encap(struct em_softc *sc, struct mbuf **m_headp)
 		m_head = m_pullup(m_head, sizeof(eh));
 		if (m_head == NULL) {
 			*m_headp = NULL;
-			error = ENOBUFS;
-			goto encap_fail;
+			return (ENOBUFS);
 		}
 		eh = *mtod(m_head, struct ether_header *);
 		M_PREPEND(m_head, sizeof(*evl), M_DONTWAIT);
 		if (m_head == NULL) {
 			*m_headp = NULL;
-			error = ENOBUFS;
-			goto encap_fail;
+			return (ENOBUFS);
 		}
 		m_head = m_pullup(m_head, sizeof(*evl));
 		if (m_head == NULL) {
 			*m_headp = NULL;
-			error = ENOBUFS;
-			goto encap_fail;
+			return (ENOBUFS);
 		}
 		evl = mtod(m_head, struct ether_vlan_header *);
 		bcopy(&eh, evl, sizeof(*evl));
@@ -1479,6 +1451,31 @@ em_encap(struct em_softc *sc, struct mbuf **m_headp)
 		*m_headp = m_head;
 	}
 
+	/*
+	 * Map the packet for DMA.
+	 */
+	tx_buffer = &sc->tx_buffer_area[sc->next_avail_tx_desc];
+	tx_buffer_last = tx_buffer;
+	map = tx_buffer->map;
+	error = bus_dmamap_load_mbuf_sg(sc->txtag, map, m_head, segs, &nsegs,
+	    BUS_DMA_NOWAIT);
+	if (error != 0) {
+		sc->no_tx_dma_setup++;
+		return (error);
+	}
+	KASSERT(nsegs != 0, ("em_encap: empty packet"));
+
+	if (nsegs > sc->num_tx_desc_avail) {
+		sc->no_tx_desc_avail2++;
+		error = ENOBUFS;
+		goto encap_fail;
+	}
+
+	if (ifp->if_hwassist > 0)
+		em_transmit_checksum_setup(sc,  m_head, &txd_upper, &txd_lower);
+	else
+		txd_upper = txd_lower = 0;
+
 	i = sc->next_avail_tx_desc;
 	if (sc->pcix_82544) {
 		txd_saved = i;