[PATCH v2 2/3] Bluetooth: L2CAP: add locking annotations for l2cap_chan_lock/unlock

[Pauli Virtanen]

Add minimal context analysis annotations to l2cap_chan_lock/unlock() and
callers required for no warnings.

Signed-off-by: Pauli Virtanen <pav@xxxxxx>
---

Notes:
    v2:
    - split code changes and adding annotations to separate patches
    
    Possibly the l2cap_ops::alloc_skb callback should have generally
    __must_hold(&chan->lock) and not just in l2cap_sock.c
    
    This would imply l2cap_chan_send() should hold the lock, but trying to
    add the annotations reveals l2cap_chan_send is called without chan->lock
    from some places:
    
    net/bluetooth/smp.c:589:2: warning: calling function 'l2cap_chan_send' requires holding mutex 'conn->smp->lock' exclusively [-Wthread-safety-analysis]
      589 |         l2cap_chan_send(chan, &msg, 1 + len, NULL);
          |         ^
    1 warning generated.
    net/bluetooth/6lowpan.c:455:8: warning: calling function 'l2cap_chan_send' requires holding mutex 'chan->lock' exclusively [-Wthread-safety-analysis]
      455 |         err = l2cap_chan_send(chan, &msg, skb->len, NULL);
          |               ^
    
    Don't know now if the context in these places allows l2cap_chan_lock()

 include/net/bluetooth/l2cap.h | 2 ++
 net/bluetooth/l2cap_core.c    | 1 +
 net/bluetooth/l2cap_sock.c    | 1 +
 3 files changed, 4 insertions(+)

diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
index ef6ce1c20a4f..53a68fc32f10 100644
--- a/include/net/bluetooth/l2cap.h
+++ b/include/net/bluetooth/l2cap.h
@@ -825,11 +825,13 @@ struct l2cap_chan *l2cap_chan_hold_unless_zero(struct l2cap_chan *c);
 void l2cap_chan_put(struct l2cap_chan *c);
 
 static inline void l2cap_chan_lock(struct l2cap_chan *chan)
+	__acquires(&chan->lock)
 {
 	mutex_lock_nested(&chan->lock, atomic_read(&chan->nesting));
 }
 
 static inline void l2cap_chan_unlock(struct l2cap_chan *chan)
+	__releases(&chan->lock)
 {
 	mutex_unlock(&chan->lock);
 }
diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 322a1895c1bd..5a76c348712d 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -4078,6 +4078,7 @@ static struct l2cap_chan *l2cap_new_connection(struct l2cap_conn *conn,
 
 static void l2cap_connect(struct l2cap_conn *conn, struct l2cap_cmd_hdr *cmd,
 			  u8 *data, u8 rsp_code)
+	__context_unsafe(/* conditional locking */)
 {
 	struct l2cap_conn_req *req = (struct l2cap_conn_req *) data;
 	struct l2cap_conn_rsp rsp;
diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index 735167f73f31..4afc5b370b97 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -1740,6 +1740,7 @@ static void l2cap_sock_state_change_cb(struct l2cap_chan *chan, int state,
 static struct sk_buff *l2cap_sock_alloc_skb_cb(struct l2cap_chan *chan,
 					       unsigned long hdr_len,
 					       unsigned long len, int nb)
+	__must_hold(&chan->lock)
 {
 	struct sock *sk = chan->data;
 	struct sk_buff *skb;
-- 
2.55.0