Bluetooth: L2CAP: Queue packets when a segment could not be allocated

When a segment could not be allocated it should be possible to resume
sending it later once previous segments complete, the only exception is
when there is no previous activity and we are unable to alocate even the
very first segment which should indicate to the caller that it would
block since that only happens on syswq the caller might need to defer to
another thread or resubmit the work.

Fixes zephyrproject-rtos#20640

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

subsys/bluetooth/host/l2cap.c

@@ -61,6 +61,12 @@
 #define l2cap_lookup_ident(conn, ident) __l2cap_lookup_ident(conn, ident, false)
 #define l2cap_remove_ident(conn, ident) __l2cap_lookup_ident(conn, ident, true)
 
+struct data_sent {
+	u16_t len;
+};
+
+#define data_sent(buf) ((struct data_sent *)net_buf_user_data(buf))
+
 static sys_slist_t servers;
 
 #endif /* CONFIG_BT_L2CAP_DYNAMIC_CHANNEL */
@@ -1163,7 +1169,9 @@ static struct net_buf *l2cap_chan_create_seg(struct bt_l2cap_le_chan *ch,
 	return seg;
 }
 
-void l2cap_chan_sdu_sent(struct bt_conn *conn, void *user_data)
+static void l2cap_chan_le_send_resume(struct bt_l2cap_le_chan *ch);
+
+static void l2cap_chan_sdu_sent(struct bt_conn *conn, void *user_data)
 {
 	struct bt_l2cap_chan *chan = user_data;
 
@@ -1172,6 +1180,17 @@ void l2cap_chan_sdu_sent(struct bt_conn *conn, void *user_data)
 	if (chan->ops->sent) {
 		chan->ops->sent(chan);
 	}
+
+	l2cap_chan_le_send_resume(BT_L2CAP_LE_CHAN(chan));
+}
+
+static void l2cap_chan_seg_sent(struct bt_conn *conn, void *user_data)
+{
+	struct bt_l2cap_chan *chan = user_data;
+
+	BT_DBG("conn %p chan %p", conn, chan);
+
+	l2cap_chan_le_send_resume(BT_L2CAP_LE_CHAN(chan));
 }
 
 static int l2cap_chan_le_send(struct bt_l2cap_le_chan *ch, struct net_buf *buf,
@@ -1182,13 +1201,14 @@ static int l2cap_chan_le_send(struct bt_l2cap_le_chan *ch, struct net_buf *buf,
 
 	/* Wait for credits */
 	if (k_sem_take(&ch->tx.credits, K_NO_WAIT)) {
-		BT_DBG("No credits to transmit packet");
+		BT_WARN("No credits to transmit packet");
 		return -EAGAIN;
 	}
 
 	seg = l2cap_chan_create_seg(ch, buf, sdu_hdr_len);
 	if (!seg) {
-		return -ENOMEM;
+		k_sem_give(&ch->tx.credits);
+		return -EAGAIN;
 	}
 
 	/* Channel may have been disconnected while waiting for a buffer */
@@ -1209,7 +1229,8 @@ static int l2cap_chan_le_send(struct bt_l2cap_le_chan *ch, struct net_buf *buf,
 		bt_l2cap_send_cb(ch->chan.conn, ch->tx.cid, seg,
 				 l2cap_chan_sdu_sent, &ch->chan);
 	} else {
-		bt_l2cap_send(ch->chan.conn, ch->tx.cid, seg);
+		bt_l2cap_send_cb(ch->chan.conn, ch->tx.cid, seg,
+				 l2cap_chan_seg_sent, &ch->chan);
 	}
 
 	/* Check if there is no credits left clear output status and notify its
@@ -1248,8 +1269,7 @@ static int l2cap_chan_le_send_sdu(struct bt_l2cap_le_chan *ch,
 		if (ret < 0) {
 			if (ret == -EAGAIN) {
 				/* Store sent data into user_data */
-				memcpy(net_buf_user_data(frag), &sent,
-				       sizeof(sent));
+				data_sent(frag)->len = sent;
 			}
 			*buf = frag;
 			return ret;
@@ -1268,8 +1288,7 @@ static int l2cap_chan_le_send_sdu(struct bt_l2cap_le_chan *ch,
 		if (ret < 0) {
 			if (ret == -EAGAIN) {
 				/* Store sent data into user_data */
-				memcpy(net_buf_user_data(frag), &sent,
-				       sizeof(sent));
+				data_sent(frag)->len = sent;
 			}
 			*buf = frag;
 			return ret;
@@ -1302,9 +1321,13 @@ static void l2cap_chan_le_send_resume(struct bt_l2cap_le_chan *ch)
 {
 	struct net_buf *buf;
 
+	if (!k_sem_count_get(&ch->tx.credits)) {
+		return;
+	}
+
 	/* Resume tx in case there are buffers in the queue */
 	while ((buf = l2cap_chan_le_get_tx_buf(ch))) {
-		u16_t sent = *((u16_t *)net_buf_user_data(buf));
+		u16_t sent = data_sent(buf)->len;
 
 		BT_DBG("buf %p sent %u", buf, sent);
 
@@ -1890,12 +1913,25 @@ int bt_l2cap_chan_send(struct bt_l2cap_chan *chan, struct net_buf *buf)
 		return bt_l2cap_br_chan_send(chan, buf);
 	}
 
+	/* Attempt to resume first since there could be data from previous
+	 * packets pending.
+	 */
+	l2cap_chan_le_send_resume(BT_L2CAP_LE_CHAN(chan));
+
+	/* Check if there are still pending segments */
+	if (BT_L2CAP_LE_CHAN(chan)->tx_buf) {
+		/* Queue buffer to be sent later */
+		data_sent(buf)->len = 0;
+		net_buf_put(&(BT_L2CAP_LE_CHAN(chan))->tx_queue, buf);
+		return 0;
+	}
+
 	err = l2cap_chan_le_send_sdu(BT_L2CAP_LE_CHAN(chan), &buf, 0);
 	if (err < 0) {
-		if (err == -EAGAIN) {
-			/* Queue buffer to be sent later */
+		if (err == -EAGAIN && data_sent(buf)->len) {
+			/* Queue buffer if at least one segment could be sent */
 			net_buf_put(&(BT_L2CAP_LE_CHAN(chan))->tx_queue, buf);
-			return *((u16_t *)net_buf_user_data(buf));
+			return data_sent(buf)->len;
 		}
 		BT_ERR("failed to send message %d", err);
 	}

subsys/bluetooth/host/l2cap_internal.h

@@ -222,8 +222,6 @@ struct bt_l2cap_br_fixed_chan {
 				.accept = _accept,		\
 			}
 
-void l2cap_chan_sdu_sent(struct bt_conn *conn, void *user_data);
-
 /* Notify L2CAP channels of a new connection */
 void bt_l2cap_connected(struct bt_conn *conn);