Bluetooth: Change l2cap chan_list to use RCU

This list has much more reads than writes, so RCU makes senses here, also
it avoid deadlock against the socket lock.
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>

net/bluetooth/l2cap_core.c

@@ -89,24 +89,36 @@ static inline void chan_put(struct l2cap_chan *c)
 
 static struct l2cap_chan *__l2cap_get_chan_by_dcid(struct l2cap_conn *conn, u16 cid)
 {
-	struct l2cap_chan *c;
+	struct l2cap_chan *c, *r = NULL;
 
-	list_for_each_entry(c, &conn->chan_l, list) {
-		if (c->dcid == cid)
-			return c;
+	rcu_read_lock();
+
+	list_for_each_entry_rcu(c, &conn->chan_l, list) {
+		if (c->dcid == cid) {
+			r = c;
+			break;
+		}
 	}
-	return NULL;
+
+	rcu_read_unlock();
+	return r;
 }
 
 static struct l2cap_chan *__l2cap_get_chan_by_scid(struct l2cap_conn *conn, u16 cid)
 {
-	struct l2cap_chan *c;
+	struct l2cap_chan *c, *r = NULL;
 
-	list_for_each_entry(c, &conn->chan_l, list) {
-		if (c->scid == cid)
-			return c;
+	rcu_read_lock();
+
+	list_for_each_entry_rcu(c, &conn->chan_l, list) {
+		if (c->scid == cid) {
+			r = c;
+			break;
+		}
 	}
-	return NULL;
+
+	rcu_read_unlock();
+	return r;
 }
 
 /* Find channel with given SCID.
@@ -115,34 +127,36 @@ static struct l2cap_chan *l2cap_get_chan_by_scid(struct l2cap_conn *conn, u16 ci
 {
 	struct l2cap_chan *c;
 
-	mutex_lock(&conn->chan_lock);
 	c = __l2cap_get_chan_by_scid(conn, cid);
 	if (c)
 		lock_sock(c->sk);
-	mutex_unlock(&conn->chan_lock);
 	return c;
 }
 
 static struct l2cap_chan *__l2cap_get_chan_by_ident(struct l2cap_conn *conn, u8 ident)
 {
-	struct l2cap_chan *c;
+	struct l2cap_chan *c, *r = NULL;
 
-	list_for_each_entry(c, &conn->chan_l, list) {
-		if (c->ident == ident)
-			return c;
+	rcu_read_lock();
+
+	list_for_each_entry_rcu(c, &conn->chan_l, list) {
+		if (c->ident == ident) {
+			r = c;
+			break;
+		}
 	}
-	return NULL;
+
+	rcu_read_unlock();
+	return r;
 }
 
 static inline struct l2cap_chan *l2cap_get_chan_by_ident(struct l2cap_conn *conn, u8 ident)
 {
 	struct l2cap_chan *c;
 
-	mutex_lock(&conn->chan_lock);
 	c = __l2cap_get_chan_by_ident(conn, ident);
 	if (c)
 		lock_sock(c->sk);
-	mutex_unlock(&conn->chan_lock);
 	return c;
 }
 
@@ -323,7 +337,7 @@ void l2cap_chan_destroy(struct l2cap_chan *chan)
 	chan_put(chan);
 }
 
-static void __l2cap_chan_add(struct l2cap_conn *conn, struct l2cap_chan *chan)
+static void l2cap_chan_add(struct l2cap_conn *conn, struct l2cap_chan *chan)
 {
 	BT_DBG("conn %p, psm 0x%2.2x, dcid 0x%4.4x", conn,
 			chan->psm, chan->dcid);
@@ -364,7 +378,7 @@ static void __l2cap_chan_add(struct l2cap_conn *conn, struct l2cap_chan *chan)
 
 	chan_hold(chan);
 
-	list_add(&chan->list, &conn->chan_l);
+	list_add_rcu(&chan->list, &conn->chan_l);
 }
 
 /* Delete channel.
@@ -381,9 +395,9 @@ static void l2cap_chan_del(struct l2cap_chan *chan, int err)
 
 	if (conn) {
 		/* Delete from channel list */
-		mutex_lock(&conn->chan_lock);
-		list_del(&chan->list);
-		mutex_unlock(&conn->chan_lock);
+		list_del_rcu(&chan->list);
+		synchronize_rcu();
+
 		chan_put(chan);
 
 		chan->conn = NULL;
@@ -750,13 +764,13 @@ static void l2cap_send_disconn_req(struct l2cap_conn *conn, struct l2cap_chan *c
 /* ---- L2CAP connections ---- */
 static void l2cap_conn_start(struct l2cap_conn *conn)
 {
-	struct l2cap_chan *chan, *tmp;
+	struct l2cap_chan *chan;
 
 	BT_DBG("conn %p", conn);
 
-	mutex_lock(&conn->chan_lock);
+	rcu_read_lock();
 
-	list_for_each_entry_safe(chan, tmp, &conn->chan_l, list) {
+	list_for_each_entry_rcu(chan, &conn->chan_l, list) {
 		struct sock *sk = chan->sk;
 
 		bh_lock_sock(sk);
@@ -780,9 +794,7 @@ static void l2cap_conn_start(struct l2cap_conn *conn)
 					&chan->conf_state)) {
 				/* l2cap_chan_close() calls list_del(chan)
 				 * so release the lock */
-				mutex_unlock(&conn->chan_lock);
 				l2cap_chan_close(chan, ECONNRESET);
-				utex_lock(&conn->chan_lock);
 				bh_unlock_sock(sk);
 				continue;
 			}
@@ -838,7 +850,7 @@ static void l2cap_conn_start(struct l2cap_conn *conn)
 		bh_unlock_sock(sk);
 	}
 
-	mutex_unlock(&conn->chan_lock);
+	rcu_read_unlock();
 }
 
 /* Find socket with cid and source bdaddr.
@@ -903,8 +915,6 @@ static void l2cap_le_conn_ready(struct l2cap_conn *conn)
 
 	sk = chan->sk;
 
-	mutex_lock(&conn->chan_lock);
-
 	hci_conn_hold(conn->hcon);
 
 	bacpy(&bt_sk(sk)->src, conn->src);
@@ -912,15 +922,13 @@ static void l2cap_le_conn_ready(struct l2cap_conn *conn)
 
 	bt_accept_enqueue(parent, sk);
 
-	__l2cap_chan_add(conn, chan);
+	l2cap_chan_add(conn, chan);
 
 	__set_chan_timer(chan, sk->sk_sndtimeo);
 
 	l2cap_state_change(chan, BT_CONNECTED);
 	parent->sk_data_ready(parent, 0);
 
-	mutex_unlock(&conn->chan_lock);
-
 clean:
 	release_sock(parent);
 }
@@ -954,9 +962,9 @@ static void l2cap_conn_ready(struct l2cap_conn *conn)
 	if (conn->hcon->out && conn->hcon->type == LE_LINK)
 		smp_conn_security(conn, conn->hcon->pending_sec_level);
 
-	mutex_lock(&conn->chan_lock);
+	rcu_read_lock();
 
-	list_for_each_entry(chan, &conn->chan_l, list) {
+	list_for_each_entry_rcu(chan, &conn->chan_l, list) {
 		struct sock *sk = chan->sk;
 
 		bh_lock_sock(sk);
@@ -976,7 +984,7 @@ static void l2cap_conn_ready(struct l2cap_conn *conn)
 		bh_unlock_sock(sk);
 	}
 
-	mutex_unlock(&conn->chan_lock);
+	rcu_read_unlock();
 }
 
 /* Notify sockets that we cannot guaranty reliability anymore */
@@ -986,16 +994,16 @@ static void l2cap_conn_unreliable(struct l2cap_conn *conn, int err)
 
 	BT_DBG("conn %p", conn);
 
-	mutex_lock(&conn->chan_lock);
+	rcu_read_lock();
 
-	list_for_each_entry(chan, &conn->chan_l, list) {
+	list_for_each_entry_rcu(chan, &conn->chan_l, list) {
 		struct sock *sk = chan->sk;
 
 		if (test_bit(FLAG_FORCE_RELIABLE, &chan->flags))
 			sk->sk_err = err;
 	}
 
-	mutex_unlock(&conn->chan_lock);
+	rcu_read_unlock();
 }
 
 static void l2cap_info_timeout(struct work_struct *work)
@@ -1087,7 +1095,6 @@ static struct l2cap_conn *l2cap_conn_add(struct hci_conn *hcon, u8 status)
 	conn->feat_mask = 0;
 
 	spin_lock_init(&conn->lock);
-	mutex_init(&conn->chan_lock);
 
 	INIT_LIST_HEAD(&conn->chan_l);
 
@@ -1102,13 +1109,6 @@ static struct l2cap_conn *l2cap_conn_add(struct hci_conn *hcon, u8 status)
 	return conn;
 }
 
-static inline void l2cap_chan_add(struct l2cap_conn *conn, struct l2cap_chan *chan)
-{
-	mutex_lock(&conn->chan_lock);
-	__l2cap_chan_add(conn, chan);
-	mutex_unlock(&conn->chan_lock);
-}
-
 /* ---- Socket interface ---- */
 
 /* Find socket with psm and source bdaddr.
@@ -1825,8 +1825,9 @@ static void l2cap_raw_recv(struct l2cap_conn *conn, struct sk_buff *skb)
 
 	BT_DBG("conn %p", conn);
 
-	mutex_lock(&conn->chan_lock);
-	list_for_each_entry(chan, &conn->chan_l, list) {
+	rcu_read_lock();
+
+	list_for_each_entry_rcu(chan, &conn->chan_l, list) {
 		struct sock *sk = chan->sk;
 		if (chan->chan_type != L2CAP_CHAN_RAW)
 			continue;
@@ -1841,7 +1842,8 @@ static void l2cap_raw_recv(struct l2cap_conn *conn, struct sk_buff *skb)
 		if (chan->ops->recv(chan->data, nskb))
 			kfree_skb(nskb);
 	}
-	mutex_unlock(&conn->chan_lock);
+
+	rcu_read_unlock();
 }
 
 /* ---- L2CAP signalling commands ---- */
@@ -2641,11 +2643,8 @@ static inline int l2cap_connect_req(struct l2cap_conn *conn, struct l2cap_cmd_hd
 
 	sk = chan->sk;
 
-	mutex_lock(&conn->chan_lock);
-
 	/* Check if we already have channel with that dcid */
 	if (__l2cap_get_chan_by_dcid(conn, scid)) {
-		mutex_unlock(&conn->chan_lock);
 		sock_set_flag(sk, SOCK_ZAPPED);
 		chan->ops->close(chan->data);
 		goto response;
@@ -2660,7 +2659,7 @@ static inline int l2cap_connect_req(struct l2cap_conn *conn, struct l2cap_cmd_hd
 
 	bt_accept_enqueue(parent, sk);
 
-	__l2cap_chan_add(conn, chan);
+	l2cap_chan_add(conn, chan);
 
 	dcid = chan->scid;
 
@@ -2691,8 +2690,6 @@ static inline int l2cap_connect_req(struct l2cap_conn *conn, struct l2cap_cmd_hd
 		status = L2CAP_CS_NO_INFO;
 	}
 
-	mutex_unlock(&conn->chan_lock);
-
 response:
 	release_sock(parent);
 
@@ -4528,9 +4525,9 @@ static int l2cap_security_cfm(struct hci_conn *hcon, u8 status, u8 encrypt)
 		del_timer(&conn->security_timer);
 	}
 
-	mutex_lock(&conn->chan_lock);
+	rcu_read_lock();
 
-	list_for_each_entry(chan, &conn->chan_l, list) {
+	list_for_each_entry_rcu(chan, &conn->chan_l, list) {
 		struct sock *sk = chan->sk;
 
 		bh_lock_sock(sk);
@@ -4608,7 +4605,7 @@ static int l2cap_security_cfm(struct hci_conn *hcon, u8 status, u8 encrypt)
 		bh_unlock_sock(sk);
 	}
 
-	mutex_unlock(&conn->chan_lock);
+	rcu_read_unlock();
 
 	return 0;
 }