MFp4 changes to fix locking issues and correct reference

count handling of station entries in hostap mode:

Input path:

o driver is now expected to find the node associated with the
  sender of a received frame; use ic_bss if none is located
o driver passes the (referenced) node into ieee80211_input for
  use within the wlan module and is responsible for cleaning up
  on return
o the antenna state is no longer passed up with each frame; this
  is now considered driver-private state and drivers are responsible
  for keeping it in the driver-private part of a node

Output path:

Revamp output path for management frames to eliminate redundant
locking that causes problems and to correct reference counting
bogosity that occurs when stations are timed out due to inactivity
(in AP mode).  On output the refcnt'd node is stashed in the pkthdr's
recvif field (yech) and retrieved by the driver.  This eliminates
an unref/ref scenario and related node table unlock/lock due to the
driver looking up the node.  This is particularly important when
stations are timed out as this causes a lock order reversal that
can result in a deadlock.  As a byproduct we also reduce the overhead
for sending management frames (minimal).  Additional fallout from
this is a change to ieee80211_encap to return a refcn't node for
tieing to the outbound frame.  Node refcnts are not reclaimed until
after a frame is completely processed (e.g. in the tx interrupt
handler).  This is especially important for timed out stations as
this deref will be the final one causing the node entry to be
reclaimed.

Additional semi-related changes:
o replace m_copym use with m_copypacket (optimization)
o add assert to verify ic_bss is never free'd during normal operation
o add comments explaining calling conventions by drivers for frames
  going in each direction
o remove extraneous code that "cannot be executed" (e.g. because
  pointers may never be null)

2 files changed, 73 insertions, 38 deletions

diff --git a/sys/dev/ath/if_ath.c b/sys/dev/ath/if_ath.c
index ba84f09..fdb0091 100644
--- a/sys/dev/ath/if_ath.c
+++ b/sys/dev/ath/if_ath.c
@@ -691,7 +691,7 @@ ath_start(struct ifnet *ifp)
 			/*
 			 * Encapsulate the packet in prep for transmission.
 			 */
-			m = ieee80211_encap(ifp, m);
+			m = ieee80211_encap(ifp, m, &ni);
 			if (m == NULL) {
 				DPRINTF(("ath_start: encapsulation failure\n"));
 				sc->sc_stats.ast_tx_encap++;
@@ -701,6 +701,18 @@ ath_start(struct ifnet *ifp)
 			if (ic->ic_flags & IEEE80211_F_WEPON)
 				wh->i_fc[1] |= IEEE80211_FC1_WEP;
 		} else {
+			/*
+			 * Hack!  The referenced node pointer is in the
+			 * rcvif field of the packet header.  This is
+			 * placed there by ieee80211_mgmt_output because
+			 * we need to hold the reference with the frame
+			 * and there's no other way (other than packet
+			 * tags which we consider too expensive to use)
+			 * to pass it along.
+			 */
+			ni = (struct ieee80211_node *) m->m_pkthdr.rcvif;
+			m->m_pkthdr.rcvif = NULL;
+
 			wh = mtod(m, struct ieee80211_frame *);
 			if ((wh->i_fc[0] & IEEE80211_FC0_SUBTYPE_MASK) ==
 			    IEEE80211_FC0_SUBTYPE_PROBE_RESP) {
@@ -720,26 +732,6 @@ ath_start(struct ifnet *ifp)
 		if (ic->ic_rawbpf)
 			bpf_mtap(ic->ic_rawbpf, m);
 
-		if (ic->ic_opmode != IEEE80211_M_STA) {
-			ni = ieee80211_find_node(ic, wh->i_addr1);
-			if (ni == NULL) {
-				/*
-				 * When not in station mode the destination
-				 * address should always be in the node table
-				 * unless this is a multicast/broadcast frame.
-				 */
-				if (!IEEE80211_IS_MULTICAST(wh->i_addr1) &&
-				    (wh->i_fc[0] & IEEE80211_FC0_TYPE_MASK) ==
-				    IEEE80211_FC0_TYPE_DATA) {
-					m_freem(m);
-					sc->sc_stats.ast_tx_nonode++;
-					goto bad;
-				}
-				ni = ic->ic_bss;
-			}
-		} else
-			ni = ic->ic_bss;
-
 		/*
 		 * TODO:
 		 * The duration field of 802.11 header should be filled.
@@ -759,6 +751,8 @@ ath_start(struct ifnet *ifp)
 			TAILQ_INSERT_TAIL(&sc->sc_txbuf, bf, bf_list);
 			mtx_unlock(&sc->sc_txbuflock);
 			ifp->if_oerrors++;
+			if (ni && ni != ic->ic_bss)
+				ieee80211_free_node(ic, ni);
 			continue;
 		}
 
@@ -1112,12 +1106,13 @@ ath_beacon_proc(void *arg, int pending)
 	struct ath_hal *ah = sc->sc_ah;
 
 	DPRINTF2(("%s: pending %u\n", __func__, pending));
-	if (ic->ic_opmode == IEEE80211_M_STA || bf == NULL || bf->bf_m == NULL) {
+	if (ic->ic_opmode == IEEE80211_M_STA ||
+	    bf == NULL || bf->bf_m == NULL) {
 		DPRINTF(("%s: ic_flags=%x bf=%p bf_m=%p\n",
 			__func__, ic->ic_flags, bf, bf ? bf->bf_m : NULL));
 		return;
 	}
-	/* update beacon to reflect PS poll state */
+	/* TODO: update beacon to reflect PS poll state */
 	if (!ath_hal_stoptxdma(ah, sc->sc_bhalq)) {
 		DPRINTF(("%s: beacon queue %u did not stop?",
 			__func__, sc->sc_bhalq));
@@ -1371,7 +1366,7 @@ ath_node_alloc(struct ieee80211com *ic)
 {
 	struct ath_node *an =
 		malloc(sizeof(struct ath_node), M_DEVBUF, M_NOWAIT | M_ZERO);
-	return an ? &an->st_node : NULL;
+	return an ? &an->an_node : NULL;
 }
 
 static void
@@ -1461,6 +1456,7 @@ ath_rx_proc(void *arg, int npending)
 	struct ath_desc *ds;
 	struct mbuf *m;
 	struct ieee80211_frame *wh, whbuf;
+	struct ieee80211_node *ni;
 	int len;
 	u_int phyerr;
 	HAL_STATUS status;
@@ -1505,6 +1501,7 @@ ath_rx_proc(void *arg, int npending)
 		len = ds->ds_rxstat.rs_datalen;
 		if (len < sizeof(struct ieee80211_frame)) {
 			DPRINTF(("ath_rx_proc: short packet %d\n", len));
+			sc->sc_stats.ast_rx_tooshort++;
 			goto rx_next;
 		}
 
@@ -1516,7 +1513,7 @@ ath_rx_proc(void *arg, int npending)
 		    IEEE80211_FC0_TYPE_CTL &&
 		    ic->ic_opmode != IEEE80211_M_MONITOR) {
 			/*
-			 * Ignore control frame received in promisc mode.
+			 * Discard control frame when not in monitor mode.
 			 */
 			DPRINTF(("ath_rx_proc: control frame\n"));
 			sc->sc_stats.ast_rx_ctl++;
@@ -1533,6 +1530,7 @@ ath_rx_proc(void *arg, int npending)
 					IEEE80211_RATE_VAL,
 				ds->ds_rxstat.rs_rssi);
 		}
+
 		m_adj(m, -IEEE80211_CRC_LEN);
 		if (wh->i_fc[1] & IEEE80211_FC1_WEP) {
 			/*
@@ -1548,10 +1546,35 @@ ath_rx_proc(void *arg, int npending)
 			 */
 			m_adj(m, -IEEE80211_WEP_CRCLEN);
 		}
-		ieee80211_input(ifp, m,
-			ds->ds_rxstat.rs_rssi,
-			ds->ds_rxstat.rs_tstamp,
-			ds->ds_rxstat.rs_antenna);
+
+		/*
+		 * Locate the node for sender, track state, and
+		 * then pass this node (referenced) up to the 802.11
+		 * layer for its use.  We are required to pass
+		 * something so we fall back to ic_bss when this frame
+		 * is from an unknown sender.
+		 */
+		if (ic->ic_opmode != IEEE80211_M_STA) {
+			ni = ieee80211_find_node(ic, wh->i_addr2);
+			if (ni == NULL)
+				ni = ieee80211_ref_node(ic->ic_bss);
+		} else
+			ni = ieee80211_ref_node(ic->ic_bss);
+		ATH_NODE(ni)->an_rx_antenna = ds->ds_rxstat.rs_antenna;
+		/*
+		 * Send frame up for processing.
+		 */
+		ieee80211_input(ifp, m, ni,
+			ds->ds_rxstat.rs_rssi, ds->ds_rxstat.rs_tstamp);
+		/*
+		 * The frame may have caused the node to be marked for
+		 * reclamation (e.g. in response to a DEAUTH message)
+		 * so use free_node here instead of unref_node.
+		 */
+		if (ni == ic->ic_bss)
+			ieee80211_unref_node(&ni);
+		else
+			ieee80211_free_node(ic, ni);
   rx_next:
 		TAILQ_INSERT_TAIL(&sc->sc_rxbuf, bf, bf_list);
 	} while (ath_rxbuf_init(sc, bf) == 0);
@@ -1681,7 +1704,7 @@ ath_tx_start(struct ath_softc *sc, struct ieee80211_node *ni, struct ath_buf *bf
 	DPRINTF2(("ath_tx_start: m %p len %u\n", m0, pktlen));
 	bus_dmamap_sync(sc->sc_dmat, bf->bf_dmamap, BUS_DMASYNC_PREWRITE);
 	bf->bf_m = m0;
-	bf->bf_node = ni;
+	bf->bf_node = ni;			/* NB: held reference */
 
 	/* setup descriptors */
 	ds = bf->bf_desc;
@@ -1792,7 +1815,7 @@ ath_tx_start(struct ath_softc *sc, struct ieee80211_node *ni, struct ath_buf *bf
 	if (an->an_tx_antenna)
 		antenna = an->an_tx_antenna;
 	else
-		antenna = ni->ni_rantenna;
+		antenna = an->an_rx_antenna;
 
 	/*
 	 * Formulate first tx descriptor with tx controls.
@@ -1865,7 +1888,8 @@ ath_tx_proc(void *arg, int npending)
 	struct ath_softc *sc = arg;
 	struct ath_hal *ah = sc->sc_ah;
 	struct ath_buf *bf;
-	struct ifnet *ifp = &sc->sc_ic.ic_if;
+	struct ieee80211com *ic = &sc->sc_ic;
+	struct ifnet *ifp = &ic->ic_if;
 	struct ath_desc *ds;
 	struct ieee80211_node *ni;
 	struct ath_node *an;
@@ -1920,6 +1944,15 @@ ath_tx_proc(void *arg, int npending)
 			sc->sc_stats.ast_tx_longretry += lr;
 			if (sr + lr)
 				an->an_tx_retr++;
+			/*
+			 * Reclaim reference to node.
+			 *
+			 * NB: the node may be reclaimed here if, for example
+			 *     this is a DEAUTH message that was sent and the
+			 *     node was timed out due to inactivity.
+			 */
+			if (ni != ic->ic_bss)
+				ieee80211_free_node(ic, ni);
 		}
 		bus_dmamap_sync(sc->sc_dmat, bf->bf_dmamap,
 		    BUS_DMASYNC_POSTWRITE);
@@ -2093,11 +2126,6 @@ ath_chan_set(struct ath_softc *sc, struct ieee80211_channel *chan)
 		}
 
 		/*
-		 * Re-enable interrupts.
-		 */
-		ath_hal_intrset(ah, sc->sc_imask);
-
-		/*
 		 * Change channels and update the h/w rate map
 		 * if we're switching; e.g. 11a to 11b/g.
 		 */
@@ -2105,6 +2133,11 @@ ath_chan_set(struct ath_softc *sc, struct ieee80211_channel *chan)
 		mode = ieee80211_chan2mode(ic, chan);
 		if (mode != sc->sc_curmode)
 			ath_setcurmode(sc, mode);
+
+		/*
+		 * Re-enable interrupts.
+		 */
+		ath_hal_intrset(ah, sc->sc_imask);
 	}
 	return 0;
 }
diff --git a/sys/dev/ath/if_athvar.h b/sys/dev/ath/if_athvar.h
index dac204a..378a0ba 100644
--- a/sys/dev/ath/if_athvar.h
+++ b/sys/dev/ath/if_athvar.h
@@ -55,13 +55,15 @@
 
 /* driver-specific node */
 struct ath_node {
-	struct ieee80211_node st_node;	/* base class */
+	struct ieee80211_node an_node;	/* base class */
 	u_int		an_tx_ok;	/* tx ok pkt */
 	u_int		an_tx_err;	/* tx !ok pkt */
 	u_int		an_tx_retr;	/* tx retry count */
 	int		an_tx_upper;	/* tx upper rate req cnt */
 	u_int		an_tx_antenna;	/* antenna for last good frame */
+	u_int		an_rx_antenna;	/* antenna for last rcvd frame */
 };
+#define	ATH_NODE(_n)	((struct ath_node *)(_n))
 
 struct ath_buf {
 	TAILQ_ENTRY(ath_buf)	bf_list;