Re: [PATCHv1] Bluetooth: Add refcnt to l2cap_conn

[Mat Martineau <mathewm@codeaurora.org>]

Andrei -

On Thu, 7 Jun 2012, Andrei Emeltchenko wrote:

> From: Andrei Emeltchenko <andrei.emeltchenko@intel.com>
>
> Adding kref to l2cap_conn helps to better handle racing when deleting
> l2cap_conn. Races are created when deleting conn from timeout and from
> the other execution path.
>
> Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>
> ---
> 	PATCHv1: fixes issues with LE
>
> include/net/bluetooth/l2cap.h |    6 +++
> net/bluetooth/l2cap_core.c    |   94 +++++++++++++++++++++++++++++++++++------
> net/bluetooth/smp.c           |    7 ++-
> 3 files changed, 91 insertions(+), 16 deletions(-)
>
> diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
> index 3d31ecd..5abfe8a 100644
> --- a/include/net/bluetooth/l2cap.h
> +++ b/include/net/bluetooth/l2cap.h
> @@ -572,6 +572,8 @@ struct l2cap_conn {
>
> 	struct list_head	chan_l;
> 	struct mutex		chan_lock;
> +
> +	struct kref		kref;
> };
>
> #define L2CAP_INFO_CL_MTU_REQ_SENT	0x01
> @@ -779,5 +781,9 @@ void l2cap_chan_set_defaults(struct l2cap_chan *chan);
> int l2cap_ertm_init(struct l2cap_chan *chan);
> void l2cap_chan_add(struct l2cap_conn *conn, struct l2cap_chan *chan);
> void l2cap_chan_del(struct l2cap_chan *chan, int err);
> +void l2cap_conn_set_timer(struct l2cap_conn *conn, struct delayed_work *work,
> +			  long timeout);
> +bool l2cap_conn_clear_timer(struct l2cap_conn *conn,
> +			    struct delayed_work *work);
>
> #endif /* __L2CAP_H */
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index eb7094c..d8c320b 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -57,6 +57,64 @@ static void l2cap_send_disconn_req(struct l2cap_conn *conn,
>
> static void l2cap_tx(struct l2cap_chan *chan, struct l2cap_ctrl *control,
> 		    struct sk_buff_head *skbs, u8 event);
> +static void l2cap_conn_del(struct hci_conn *hcon, int err);
> +
> +/* ---- L2CAP connections ---- */
> +
> +static void l2cap_conn_get(struct l2cap_conn *conn)
> +{
> +	BT_DBG("conn %p", conn);
> +
> +	kref_get(&conn->kref);
> +}
> +
> +static void l2cap_conn_destroy(struct kref *kref)
> +{
> +	struct l2cap_conn *conn = container_of(kref, struct l2cap_conn, kref);
> +
> +	BT_DBG("conn %p", conn);
> +
> +	l2cap_conn_del(conn->hcon, 0);
> +}
> +
> +static int l2cap_conn_put(struct l2cap_conn *conn)
> +{
> +	BT_DBG("conn %p", conn);
> +
> +	/* conn might be NULL, was checked before in l2cap_conn_del */
> +	if (!conn)
> +		return 1;
> +
> +	return kref_put(&conn->kref, &l2cap_conn_destroy);
> +}
> +
> +void l2cap_conn_set_timer(struct l2cap_conn *conn, struct delayed_work *work,
> +			  long timeout)
> +{
> +	BT_DBG("conn %p timeout %ld", conn, timeout);
> +
> +	/* If delayed work cancelled do not hold(conn)
> +	   since it is already done with previous set_timer */
> +	if (!cancel_delayed_work(work))
> +		l2cap_conn_get(conn);
> +
> +	schedule_delayed_work(work, timeout);
> +}
> +
> +bool l2cap_conn_clear_timer(struct l2cap_conn *conn, struct delayed_work *work)
> +{
> +	bool ret;
> +
> +	BT_DBG("conn %p", conn);
> +
> +	/* put(conn) if delayed work cancelled otherwise it
> +	   is done in delayed work function */
> +	ret = cancel_delayed_work(work);
> +	if (ret)
> +		l2cap_conn_put(conn);
> +
> +	return ret;
> +}
>
> /* ---- L2CAP channels ---- */
>
> @@ -1321,10 +1379,8 @@ static void l2cap_conn_del(struct hci_conn *hcon, int err)
> 	if (conn->info_state & L2CAP_INFO_FEAT_MASK_REQ_SENT)
> 		cancel_delayed_work_sync(&conn->info_timer);
>
> -	if (test_and_clear_bit(HCI_CONN_LE_SMP_PEND, &hcon->flags)) {
> -		cancel_delayed_work_sync(&conn->security_timer);
> +	if (test_and_clear_bit(HCI_CONN_LE_SMP_PEND, &hcon->flags))
> 		smp_chan_destroy(conn);
> -	}
>
> 	hcon->l2cap_data = NULL;
> 	kfree(conn);
> @@ -1333,9 +1389,9 @@ static void l2cap_conn_del(struct hci_conn *hcon, int err)
> static void security_timeout(struct work_struct *work)
> {
> 	struct l2cap_conn *conn = container_of(work, struct l2cap_conn,
> -						security_timer.work);
> +					       security_timer.work);
>
> -	l2cap_conn_del(conn->hcon, ETIMEDOUT);
> +	l2cap_conn_put(conn);
> }
>
> static struct l2cap_conn *l2cap_conn_add(struct hci_conn *hcon, u8 status)
> @@ -1377,6 +1433,8 @@ static struct l2cap_conn *l2cap_conn_add(struct hci_conn *hcon, u8 status)
>
> 	INIT_LIST_HEAD(&conn->chan_l);
>
> +	kref_init(&conn->kref);
> +
> 	if (hcon->type == LE_LINK)
> 		INIT_DELAYED_WORK(&conn->security_timer, security_timeout);
> 	else
> @@ -5286,8 +5344,10 @@ static void l2cap_recv_frame(struct l2cap_conn *conn, struct sk_buff *skb)
> 		break;
>
> 	case L2CAP_CID_SMP:
> -		if (smp_sig_channel(conn, skb))
> -			l2cap_conn_del(conn->hcon, EACCES);
> +		if (smp_sig_channel(conn, skb)) {
> +			l2cap_conn_clear_timer(conn, &conn->security_timer);
> +			l2cap_conn_put(conn);
> +		}
> 		break;
>
> 	default:
> @@ -5331,7 +5391,7 @@ int l2cap_connect_ind(struct hci_dev *hdev, bdaddr_t *bdaddr)
>
> int l2cap_connect_cfm(struct hci_conn *hcon, u8 status)
> {
> -	struct l2cap_conn *conn;
> +	struct l2cap_conn *conn = hcon->l2cap_data;
>
> 	BT_DBG("hcon %p bdaddr %s status %d", hcon, batostr(&hcon->dst), status);
>
> @@ -5339,8 +5399,12 @@ int l2cap_connect_cfm(struct hci_conn *hcon, u8 status)
> 		conn = l2cap_conn_add(hcon, status);
> 		if (conn)
> 			l2cap_conn_ready(conn);
> -	} else
> -		l2cap_conn_del(hcon, bt_to_errno(status));
> +	} else {
> +		if (hcon->type == LE_LINK)
> +			l2cap_conn_clear_timer(conn, &conn->security_timer);
> +
> +		l2cap_conn_put(conn);
> +	}
>
> 	return 0;
> }
> @@ -5358,9 +5422,14 @@ int l2cap_disconn_ind(struct hci_conn *hcon)
>
> int l2cap_disconn_cfm(struct hci_conn *hcon, u8 reason)
> {
> +	struct l2cap_conn *conn = hcon->l2cap_data;
> 	BT_DBG("hcon %p reason %d", hcon, reason);
>
> -	l2cap_conn_del(hcon, bt_to_errno(reason));
> +	if (hcon->type == LE_LINK)
> +		l2cap_conn_clear_timer(conn, &conn->security_timer);
> +
> +	l2cap_conn_put(conn);
> +
> 	return 0;
> }
>
> @@ -5393,7 +5462,8 @@ int l2cap_security_cfm(struct hci_conn *hcon, u8 status, u8 encrypt)
> 	if (hcon->type == LE_LINK) {
> 		if (!status && encrypt)
> 			smp_distribute_keys(conn, 0);
> -		cancel_delayed_work(&conn->security_timer);
> +
> +		l2cap_conn_clear_timer(conn, &conn->security_timer);
> 	}
>
> 	mutex_lock(&conn->chan_lock);
> diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
> index ff4835b..7aaf849 100644
> --- a/net/bluetooth/smp.c
> +++ b/net/bluetooth/smp.c
> @@ -186,8 +186,7 @@ static void smp_send_cmd(struct l2cap_conn *conn, u8 code, u16 len, void *data)
> 	skb->priority = HCI_PRIO_MAX;
> 	hci_send_acl(conn->hchan, skb, 0);
>
> -	cancel_delayed_work_sync(&conn->security_timer);
> -	schedule_delayed_work(&conn->security_timer, SMP_TIMEOUT);
> +	l2cap_conn_set_timer(conn, &conn->security_timer, SMP_TIMEOUT);
> }
>
> static __u8 authreq_to_seclevel(__u8 authreq)
> @@ -268,7 +267,7 @@ static void smp_failure(struct l2cap_conn *conn, u8 reason, u8 send)
> 			 hcon->dst_type, reason);
>
> 	if (test_and_clear_bit(HCI_CONN_LE_SMP_PEND, &conn->hcon->flags)) {
> -		cancel_delayed_work_sync(&conn->security_timer);
> +		l2cap_conn_clear_timer(conn, &conn->security_timer);
> 		smp_chan_destroy(conn);
> 	}
> }
> @@ -996,7 +995,7 @@ int smp_distribute_keys(struct l2cap_conn *conn, __u8 force)
>
> 	if (conn->hcon->out || force) {
> 		clear_bit(HCI_CONN_LE_SMP_PEND, &conn->hcon->flags);
> -		cancel_delayed_work_sync(&conn->security_timer);
> +		l2cap_conn_clear_timer(conn, &conn->security_timer);
> 		smp_chan_destroy(conn);
> 	}
>
> -- 
> 1.7.9.5

I think it's a very good thing to add reference counting, thanks for 
doing this work.

I'd like to see the code be more strict about matching the gets & puts 
up with actual assignments to l2cap_conn pointers:

  * Make sure one reference count is held for hcon->l2cap_data (your 
patch already does this)
  * l2cap_conn_put when setting hcon->l2cap_data to NULL
  * l2cap_conn_get when assigning l2cap_chan->conn
  * l2cap_conn_put when setting l2cap_chan->conn to NULL or freeing 
l2cap_chan
  * Use l2cap_conn_get/put whenever there's a reference to an 
l2cap_conn struct in an active timer.  You set this up for the 
security_timer, but info_timer could use it too.

Right now, l2cap_conn_del is only called when the reference count goes 
to 0.  If l2cap_conn reference counts are added to l2cap_chan, then 
the reference count wouldn't be 0 if the ACL was forced to close, and 
the l2cap_chans would not get cleaned up.  I think it would help to 
make l2cap_conn_del clean up the channels and connection state, and 
then have l2cap_conn_destroy free the structure.  l2cap_conn_destroy 
would only have to call l2cap_conn_del if it hadn't been done yet.


Regards,

--
Mat Martineau
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum