Hi Gustavo,
On Sat, Dec 17, 2011 at 07:29:39PM -0200, Gustavo F. Padovan wrote:
> From: "Gustavo F. Padovan" <padovan@xxxxxxxxxxxxxx>
>
> This list has much more reads than writes, so RCU makes senses here, also
> it avoid deadlock against the socket lock.
>
> Signed-off-by: Gustavo F. Padovan <padovan@xxxxxxxxxxxxxx>
> ---
> net/bluetooth/l2cap_core.c | 117 +++++++++++++++++++++----------------------
> 1 files changed, 57 insertions(+), 60 deletions(-)
>
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index d616519..a212295 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;
> + }
> }
> +
> + rcu_read_unlock();
> return NULL;
> }
>
> 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);
OK, I see why this works. BTW: IMO the mutex and rcu patches shall be
amended, otherwise we do unneeded work of implementing mutexes and then
changing them to RCU.
Best regards
Andrei Emeltchenko
> 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;
> }
> --
> 1.7.6.4
>
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