Make sure that tx_buffer->next_eop is properly set before we bump the number

of available descriptors, such that the interrupt handler doesn't attempt
to complete partially initialized descriptors.  Seems to fix the watchdog
timeouts reported by various people.

Tested by Mattieu Baptiste and Gregor Best.
ok mikeb@

1 files changed, 13 insertions, 7 deletions

diff --git a/sys/dev/pci/if_em.c b/sys/dev/pci/if_em.c
index 94d906b6572..9b860d5a72f 100644
--- a/sys/dev/pci/if_em.c
+++ b/sys/dev/pci/if_em.c
@@ -31,7 +31,7 @@ POSSIBILITY OF SUCH DAMAGE.
 
 ***************************************************************************/
 
-/* $OpenBSD: if_em.c,v 1.306 2015/09/30 11:25:08 kettenis Exp $ */
+/* $OpenBSD: if_em.c,v 1.307 2015/10/06 15:21:16 kettenis Exp $ */
 /* $FreeBSD: if_em.c,v 1.46 2004/09/29 18:28:28 mlaier Exp $ */
 
 #include <dev/pci/if_em.h>
@@ -1210,12 +1210,6 @@ em_encap(struct em_softc *sc, struct mbuf *m_head)
 		}
 	}
 
-	sc->next_avail_tx_desc = i;
-	if (sc->pcix_82544)
-		atomic_sub_int(&sc->num_tx_desc_avail, txd_used);
-	else
-		atomic_sub_int(&sc->num_tx_desc_avail, map->dm_nsegs);
-
 #if NVLAN > 0
 	/* Find out if we are in VLAN mode */
 	if (m_head->m_flags & M_VLANTAG) {
@@ -1249,6 +1243,14 @@ em_encap(struct em_softc *sc, struct mbuf *m_head)
 	tx_buffer = &sc->tx_buffer_area[first];
 	tx_buffer->next_eop = last;
 
+	membar_producer();
+
+	sc->next_avail_tx_desc = i;
+	if (sc->pcix_82544)
+		atomic_sub_int(&sc->num_tx_desc_avail, txd_used);
+	else
+		atomic_sub_int(&sc->num_tx_desc_avail, map->dm_nsegs);
+
 	/* 
 	 * Advance the Transmit Descriptor Tail (Tdt),
 	 * this tells the E1000 that this frame is
@@ -2378,6 +2380,8 @@ em_transmit_checksum_setup(struct em_softc *sc, struct mbuf *mp,
 	tx_buffer->m_head = NULL;
 	tx_buffer->next_eop = -1;
 
+	membar_producer();
+
 	if (++curr_txd == sc->num_tx_desc)
 		curr_txd = 0;
 
@@ -2403,6 +2407,8 @@ em_txeof(struct em_softc *sc)
 	if (sc->num_tx_desc_avail == sc->num_tx_desc)
 		return;
 
+	membar_consumer();
+
 	first = sc->next_tx_to_clean;
 	tx_desc = &sc->tx_desc_base[first];
 	tx_buffer = &sc->tx_buffer_area[first];