ath9k: prevent aggregation session deadlocks

Waiting for all subframes of an existing aggregation session to drain
before allowing mac80211 to start a new one is fragile and deadlocks
caused by this behavior have been observed.

Since mac80211 has proper synchronization for aggregation session
start/stop handling, a better approach to session handling is to simply
allow mac80211 to start a new session at any time. This requires
changing the code to discard any packets outside of the BlockAck window
in the A-MPDU software retry code.

This patch implements the above and also simplifies the code.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

4 files changed, 46 insertions, 114 deletions

diff --git a/drivers/net/wireless/ath/ath9k/ath9k.h b/drivers/net/wireless/ath/ath9k/ath9k.h
index 366002f266f8..42b03dc39d14 100644
--- a/drivers/net/wireless/ath/ath9k/ath9k.h
+++ b/drivers/net/wireless/ath/ath9k/ath9k.h
@@ -251,10 +251,9 @@ struct ath_atx_tid {
         int tidno;
         int baw_head;   /* first un-acked tx buffer */
         int baw_tail;   /* next unused tx buffer slot */
-        int sched;
-        int paused;
-        u8 state;
-        bool stop_cb;
+        bool sched;
+        bool paused;
+        bool active;
 };
 
 struct ath_node {
@@ -275,10 +274,6 @@ struct ath_node {
 #endif
 };
 
-#define AGGR_CLEANUP         BIT(1)
-#define AGGR_ADDBA_COMPLETE  BIT(2)
-#define AGGR_ADDBA_PROGRESS  BIT(3)
-
 struct ath_tx_control {
         struct ath_txq *txq;
         struct ath_node *an;
@@ -352,8 +347,7 @@ void ath_tx_tasklet(struct ath_softc *sc);
 void ath_tx_edma_tasklet(struct ath_softc *sc);
 int ath_tx_aggr_start(struct ath_softc *sc, struct ieee80211_sta *sta,
                       u16 tid, u16 *ssn);
-bool ath_tx_aggr_stop(struct ath_softc *sc, struct ieee80211_sta *sta, u16 tid,
-                      bool flush);
+void ath_tx_aggr_stop(struct ath_softc *sc, struct ieee80211_sta *sta, u16 tid);
 void ath_tx_aggr_resume(struct ath_softc *sc, struct ieee80211_sta *sta, u16 tid);
 
 void ath_tx_aggr_wakeup(struct ath_softc *sc, struct ath_node *an);
diff --git a/drivers/net/wireless/ath/ath9k/main.c b/drivers/net/wireless/ath/ath9k/main.c
index 2382d1262e7f..5092ecae7706 100644
--- a/drivers/net/wireless/ath/ath9k/main.c
+++ b/drivers/net/wireless/ath/ath9k/main.c
@@ -1709,7 +1709,8 @@ static int ath9k_ampdu_action(struct ieee80211_hw *hw,
                 flush = true;
         case IEEE80211_AMPDU_TX_STOP_CONT:
                 ath9k_ps_wakeup(sc);
-                if (ath_tx_aggr_stop(sc, sta, tid, flush))
+                ath_tx_aggr_stop(sc, sta, tid);
+                if (!flush)
                         ieee80211_stop_tx_ba_cb_irqsafe(vif, sta->addr, tid);
                 ath9k_ps_restore(sc);
                 break;
diff --git a/drivers/net/wireless/ath/ath9k/rc.c b/drivers/net/wireless/ath/ath9k/rc.c
index aa4d368d8d3d..7eb1f4b458e4 100644
--- a/drivers/net/wireless/ath/ath9k/rc.c
+++ b/drivers/net/wireless/ath/ath9k/rc.c
@@ -1227,10 +1227,7 @@ static bool ath_tx_aggr_check(struct ath_softc *sc, struct ieee80211_sta *sta,
                 return false;
 
         txtid = ATH_AN_2_TID(an, tidno);
-
-        if (!(txtid->state & (AGGR_ADDBA_COMPLETE | AGGR_ADDBA_PROGRESS)))
-                        return true;
-        return false;
+        return !txtid->active;
 }
 
 
diff --git a/drivers/net/wireless/ath/ath9k/xmit.c b/drivers/net/wireless/ath/ath9k/xmit.c
index 14bb3354ea64..1c9b1bac8b0d 100644
--- a/drivers/net/wireless/ath/ath9k/xmit.c
+++ b/drivers/net/wireless/ath/ath9k/xmit.c
@@ -125,24 +125,6 @@ static void ath_tx_queue_tid(struct ath_txq *txq, struct ath_atx_tid *tid)
         list_add_tail(&ac->list, &txq->axq_acq);
 }
 
-static void ath_tx_resume_tid(struct ath_softc *sc, struct ath_atx_tid *tid)
-{
-        struct ath_txq *txq = tid->ac->txq;
-
-        WARN_ON(!tid->paused);
-
-        ath_txq_lock(sc, txq);
-        tid->paused = false;
-
-        if (skb_queue_empty(&tid->buf_q))
-                goto unlock;
-
-        ath_tx_queue_tid(txq, tid);
-        ath_txq_schedule(sc, txq);
-unlock:
-        ath_txq_unlock_complete(sc, txq);
-}
-
 static struct ath_frame_info *get_frame_info(struct sk_buff *skb)
 {
         struct ieee80211_tx_info *tx_info = IEEE80211_SKB_CB(skb);
@@ -164,20 +146,7 @@ static void ath_set_rates(struct ieee80211_vif *vif, struct ieee80211_sta *sta,
                                ARRAY_SIZE(bf->rates));
 }
 
-static void ath_tx_clear_tid(struct ath_softc *sc, struct ath_atx_tid *tid)
-{
-        tid->state &= ~AGGR_ADDBA_COMPLETE;
-        tid->state &= ~AGGR_CLEANUP;
-        if (!tid->stop_cb)
-                return;
-
-        ieee80211_start_tx_ba_cb_irqsafe(tid->an->vif, tid->an->sta->addr,
-                                         tid->tidno);
-        tid->stop_cb = false;
-}
-
-static void ath_tx_flush_tid(struct ath_softc *sc, struct ath_atx_tid *tid,
-                             bool flush_packets)
+static void ath_tx_flush_tid(struct ath_softc *sc, struct ath_atx_tid *tid)
 {
         struct ath_txq *txq = tid->ac->txq;
         struct sk_buff *skb;
@@ -194,15 +163,16 @@ static void ath_tx_flush_tid(struct ath_softc *sc, struct ath_atx_tid *tid,
         while ((skb = __skb_dequeue(&tid->buf_q))) {
                 fi = get_frame_info(skb);
                 bf = fi->bf;
-                if (!bf && !flush_packets)
-                        bf = ath_tx_setup_buffer(sc, txq, tid, skb);
 
                 if (!bf) {
-                        ieee80211_free_txskb(sc->hw, skb);
-                        continue;
+                        bf = ath_tx_setup_buffer(sc, txq, tid, skb);
+                        if (!bf) {
+                                ieee80211_free_txskb(sc->hw, skb);
+                                continue;
+                        }
                 }
 
-                if (fi->retries || flush_packets) {
+                if (fi->retries) {
                         list_add_tail(&bf->list, &bf_head);
                         ath_tx_update_baw(sc, tid, bf->bf_state.seqno);
                         ath_tx_complete_buf(sc, bf, txq, &bf_head, &ts, 0);
@@ -213,10 +183,7 @@ static void ath_tx_flush_tid(struct ath_softc *sc, struct ath_atx_tid *tid,
                 }
         }
 
-        if (tid->baw_head == tid->baw_tail)
-                ath_tx_clear_tid(sc, tid);
-
-        if (sendbar && !flush_packets) {
+        if (sendbar) {
                 ath_txq_unlock(sc, txq);
                 ath_send_bar(tid, tid->seq_start);
                 ath_txq_lock(sc, txq);
@@ -499,19 +466,19 @@ static void ath_tx_complete_aggr(struct ath_softc *sc, struct ath_txq *txq,
                 tx_info = IEEE80211_SKB_CB(skb);
                 fi = get_frame_info(skb);
 
-                if (ATH_BA_ISSET(ba, ATH_BA_INDEX(seq_st, seqno))) {
+                if (!BAW_WITHIN(tid->seq_start, tid->baw_size, seqno)) {
+                        /*
+                         * Outside of the current BlockAck window,
+                         * maybe part of a previous session
+                         */
+                        txfail = 1;
+                } else if (ATH_BA_ISSET(ba, ATH_BA_INDEX(seq_st, seqno))) {
                         /* transmit completion, subframe is
                          * acked by block ack */
                         acked_cnt++;
                 } else if (!isaggr && txok) {
                         /* transmit completion */
                         acked_cnt++;
-                } else if (tid->state & AGGR_CLEANUP) {
-                        /*
-                         * cleanup in progress, just fail
-                         * the un-acked sub-frames
-                         */
-                        txfail = 1;
                 } else if (flush) {
                         txpending = 1;
                 } else if (fi->retries < ATH_MAX_SW_RETRIES) {
@@ -535,7 +502,7 @@ static void ath_tx_complete_aggr(struct ath_softc *sc, struct ath_txq *txq,
                 if (bf_next != NULL || !bf_last->bf_stale)
                         list_move_tail(&bf->list, &bf_head);
 
-                if (!txpending || (tid->state & AGGR_CLEANUP)) {
+                if (!txpending) {
                         /*
                          * complete the acked-ones/xretried ones; update
                          * block-ack window
@@ -609,9 +576,6 @@ static void ath_tx_complete_aggr(struct ath_softc *sc, struct ath_txq *txq,
                 ath_txq_lock(sc, txq);
         }
 
-        if (tid->state & AGGR_CLEANUP)
-                ath_tx_flush_tid(sc, tid, false);
-
         rcu_read_unlock();
 
         if (needreset)
@@ -1244,9 +1208,6 @@ int ath_tx_aggr_start(struct ath_softc *sc, struct ieee80211_sta *sta,
         an = (struct ath_node *)sta->drv_priv;
         txtid = ATH_AN_2_TID(an, tid);
 
-        if (txtid->state & (AGGR_CLEANUP | AGGR_ADDBA_COMPLETE))
-                return -EAGAIN;
-
         /* update ampdu factor/density, they may have changed. This may happen
          * in HT IBSS when a beacon with HT-info is received after the station
          * has already been added.
@@ -1258,7 +1219,7 @@ int ath_tx_aggr_start(struct ath_softc *sc, struct ieee80211_sta *sta,
                 an->mpdudensity = density;
         }
 
-        txtid->state |= AGGR_ADDBA_PROGRESS;
+        txtid->active = true;
         txtid->paused = true;
         *ssn = txtid->seq_start = txtid->seq_next;
         txtid->bar_index = -1;
@@ -1269,45 +1230,17 @@ int ath_tx_aggr_start(struct ath_softc *sc, struct ieee80211_sta *sta,
         return 0;
 }
 
-bool ath_tx_aggr_stop(struct ath_softc *sc, struct ieee80211_sta *sta, u16 tid,
-                      bool flush)
+void ath_tx_aggr_stop(struct ath_softc *sc, struct ieee80211_sta *sta, u16 tid)
 {
         struct ath_node *an = (struct ath_node *)sta->drv_priv;
         struct ath_atx_tid *txtid = ATH_AN_2_TID(an, tid);
         struct ath_txq *txq = txtid->ac->txq;
-        bool ret = !flush;
-
-        if (flush)
-                txtid->stop_cb = false;
-
-        if (txtid->state & AGGR_CLEANUP)
-                return false;
-
-        if (!(txtid->state & AGGR_ADDBA_COMPLETE)) {
-                txtid->state &= ~AGGR_ADDBA_PROGRESS;
-                return ret;
-        }
 
         ath_txq_lock(sc, txq);
+        txtid->active = false;
         txtid->paused = true;
-
-        /*
-         * If frames are still being transmitted for this TID, they will be
-         * cleaned up during tx completion. To prevent race conditions, this
-         * TID can only be reused after all in-progress subframes have been
-         * completed.
-         */
-        if (txtid->baw_head != txtid->baw_tail) {
-                txtid->state |= AGGR_CLEANUP;
-                ret = false;
-                txtid->stop_cb = !flush;
-        } else {
-                txtid->state &= ~AGGR_ADDBA_COMPLETE;
-        }
-
-        ath_tx_flush_tid(sc, txtid, flush);
+        ath_tx_flush_tid(sc, txtid);
         ath_txq_unlock_complete(sc, txq);
-        return ret;
 }
 
 void ath_tx_aggr_sleep(struct ieee80211_sta *sta, struct ath_softc *sc,
@@ -1371,18 +1304,28 @@ void ath_tx_aggr_wakeup(struct ath_softc *sc, struct ath_node *an)
         }
 }
 
-void ath_tx_aggr_resume(struct ath_softc *sc, struct ieee80211_sta *sta, u16 tid)
+void ath_tx_aggr_resume(struct ath_softc *sc, struct ieee80211_sta *sta,
+                        u16 tidno)
 {
-        struct ath_atx_tid *txtid;
+        struct ath_atx_tid *tid;
         struct ath_node *an;
+        struct ath_txq *txq;
 
         an = (struct ath_node *)sta->drv_priv;
+        tid = ATH_AN_2_TID(an, tidno);
+        txq = tid->ac->txq;
 
-        txtid = ATH_AN_2_TID(an, tid);
-        txtid->baw_size = IEEE80211_MIN_AMPDU_BUF << sta->ht_cap.ampdu_factor;
-        txtid->state |= AGGR_ADDBA_COMPLETE;
-        txtid->state &= ~AGGR_ADDBA_PROGRESS;
-        ath_tx_resume_tid(sc, txtid);
+        ath_txq_lock(sc, txq);
+
+        tid->baw_size = IEEE80211_MIN_AMPDU_BUF << sta->ht_cap.ampdu_factor;
+        tid->paused = false;
+
+        if (!skb_queue_empty(&tid->buf_q)) {
+                ath_tx_queue_tid(txq, tid);
+                ath_txq_schedule(sc, txq);
+        }
+
+        ath_txq_unlock_complete(sc, txq);
 }
 
 /********************/
@@ -2431,13 +2374,10 @@ void ath_tx_node_init(struct ath_softc *sc, struct ath_node *an)
                 tid->baw_head  = tid->baw_tail = 0;
                 tid->sched     = false;
                 tid->paused    = false;
-                tid->state &= ~AGGR_CLEANUP;
+                tid->active        = false;
                 __skb_queue_head_init(&tid->buf_q);
                 acno = TID_TO_WME_AC(tidno);
                 tid->ac = &an->ac[acno];
-                tid->state &= ~AGGR_ADDBA_COMPLETE;
-                tid->state &= ~AGGR_ADDBA_PROGRESS;
-                tid->stop_cb = false;
         }
 
         for (acno = 0, ac = &an->ac[acno];
@@ -2474,7 +2414,7 @@ void ath_tx_node_cleanup(struct ath_softc *sc, struct ath_node *an)
                 }
 
                 ath_tid_drain(sc, txq, tid);
-                ath_tx_clear_tid(sc, tid);
+                tid->active = false;
 
                 ath_txq_unlock(sc, txq);
         }