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>

1 files changed, 58 insertions, 61 deletions

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index d6165199fc8b..a1766adee397 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/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;
 }