Re: [RFCv2 6/8] Bluetooth: Lock the L2CAP channel when sending

[Gustavo Padovan <gustavo@padovan.org>]

Hi Mat,

* Mat Martineau <mathewm@codeaurora.org> [2012-04-27 16:50:53 -0700]:

> The ERTM and streaming mode transmit queue must only be accessed while
> the L2CAP channel lock is held.  Locking the channel before calling
> l2cap_chan_send ensures that multiple threads cannot simultaneously
> manipulate the queue when sending and receiving concurrently.
> 
> L2CAP channel locking had previously moved to the l2cap_chan struct
> instead of the associated socket, so some of the old socket locking
> can also be removed in this patch.
> 
> Signed-off-by: Mat Martineau <mathewm@codeaurora.org>
> ---
>  include/net/bluetooth/bluetooth.h |    2 --
>  net/bluetooth/l2cap_sock.c        |   15 ++++++++-------
>  2 files changed, 8 insertions(+), 9 deletions(-)
> 
> diff --git a/include/net/bluetooth/bluetooth.h b/include/net/bluetooth/bluetooth.h
> index 2fb268f..90678a9 100644
> --- a/include/net/bluetooth/bluetooth.h
> +++ b/include/net/bluetooth/bluetooth.h
> @@ -256,12 +256,10 @@ static inline struct sk_buff *bt_skb_send_alloc(struct sock *sk,
>  {
>  	struct sk_buff *skb;
>  
> -	release_sock(sk);
>  	if ((skb = sock_alloc_send_skb(sk, len + BT_SKB_RESERVE, nb, err))) {
>  		skb_reserve(skb, BT_SKB_RESERVE);
>  		bt_cb(skb)->incoming  = 0;
>  	}
> -	lock_sock(sk);
>  
>  	if (!skb && *err)
>  		return NULL;
> diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
> index 82b6368..ac8ce10 100644
> --- a/net/bluetooth/l2cap_sock.c
> +++ b/net/bluetooth/l2cap_sock.c
> @@ -716,16 +716,13 @@ static int l2cap_sock_sendmsg(struct kiocb *iocb, struct socket *sock, struct ms
>  	if (msg->msg_flags & MSG_OOB)
>  		return -EOPNOTSUPP;
>  
> -	lock_sock(sk);
> -
> -	if (sk->sk_state != BT_CONNECTED) {
> -		release_sock(sk);
> +	if (sk->sk_state != BT_CONNECTED)
>  		return -ENOTCONN;
> -	}
>  
> +	l2cap_chan_lock(chan);
>  	err = l2cap_chan_send(chan, msg, len, sk->sk_priority);
> +	l2cap_chan_unlock(chan);

I would move these l2cap_chan_{,un}lock calls to inside
l2cap_chan_send(). The less we use l2cap_chan_* functions here the
better.
>  
> -	release_sock(sk);
>  	return err;
>  }
>  
> @@ -936,9 +933,13 @@ static struct sk_buff *l2cap_sock_alloc_skb_cb(struct l2cap_chan *chan,
>  	struct sk_buff *skb;
>  	int err;
>  
> +	l2cap_chan_unlock(chan);
> +
>  	skb = bt_skb_send_alloc(chan->sk, len, nb, &err);
>  	if (!skb)
> -		return (ERR_PTR(err));
> +		skb = ERR_PTR(err);
> +
> +	l2cap_chan_lock(chan);

I would suggest the same here, but it might not be worth, since we would
need to create wrapper to call alloc_skb().

	Gustavo