Re: [PATCH] Bluetooth: Use non locking get_chan and explicit lock

Hi Marcel,

On Sat, Jan 21, 2012 at 05:41:34PM +0100, Marcel Holtmann wrote:

Hi Andrei,

quoted

For receiving ACL packets use __l2cap_get_chan_by_scid which is not
locking sk and explicitly lock sk after checking that it is exist.
Code looks nicer since now it is surrounded by lock/release.

Signed-off-by: Andrei Emeltchenko <redacted>
---
 net/bluetooth/l2cap_core.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index d16ad49..53dbfd3 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c

@@ -4243,7 +4243,7 @@ static inline int l2cap_data_channel(struct l2cap_conn *conn, u16 cid, struct sk
 	u16 tx_seq;
 	int len;
 
-	chan = l2cap_get_chan_by_scid(conn, cid);
+	chan = __l2cap_get_chan_by_scid(conn, cid);
 	if (!chan) {
 		if (cid == L2CAP_CID_A2MP) {
 			chan = a2mp_channel_create(conn, skb);

@@ -4255,6 +4255,8 @@ static inline int l2cap_data_channel(struct l2cap_conn *conn, u16 cid, struct sk
 	}
 
 	sk = chan->sk;
+	if (sk)
+		lock_sock(sk);

this is the part I clearly do not like. This is pretty nasty conditional
locking. We need to figure out something better.

Actually l2cap_data_channel function ends with:

        <------8<--------------------
        |  if (sk)
        |          release_sock(sk);
        |
        <------8<--------------------

So in _this_ case it looks consistent. But I agree that generally it does
not looks nice. The reason for that is l2cap_chan is locked with socket
lock. Maybe we could create mutex l2cap_lock and functions like
lock_chan(chan) / unlock_chan(chan) and change socket locks in l2cap_core
with these new locks?

Best regards 
Andrei Emeltchenko