[Bluez-devel] Re: L2CAP non-blocking socket nasty race conditions

[Marcel Holtmann <marcel@holtmann.org>]

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Hi Jean,

> 	So, in other words I've just moved a tight loop from my code
> to the kernel code (or glibc). Which means it seems that we only have
> half of the solution (or maybe it's normal poll behavior ?).

I had the attached patch in mind. Please check if this also works for
you, because it should produce less code execution. I think we can also
remove the list_empty() check from bt_sock_listen_poll(), because the
list_for_each_safe() gives us the same result.

> 	I think at that point we will need to get advice from the
> network gurus on how socket notification works.

I already checked the IPV4 code and they also work with an accept queue,
but at the moment I don't understand when they put the new socket on it
and how they keep track of it.

Regards

Marcel


[-- Attachment #2: patch --]
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===== net/bluetooth/af_bluetooth.c 1.27 vs edited =====
--- 1.27/net/bluetooth/af_bluetooth.c	Wed Jan 14 21:56:53 2004
+++ edited/net/bluetooth/af_bluetooth.c	Thu Feb  5 13:44:56 2004
@@ -236,15 +236,34 @@
 	return err ? : copied;
 }
 
+static __inline__ unsigned int bt_sock_listen_poll(struct sock *parent, poll_table *wait)
+{
+	struct list_head *p, *n;
+	struct sock *sk;
+
+	if (list_empty(&bt_sk(parent)->accept_q))
+		return 0;
+
+	list_for_each_safe(p, n, &bt_sk(parent)->accept_q) {
+		sk = (struct sock *) list_entry(p, struct bt_sock, accept_q);
+		if (sk->sk_state == BT_CONNECTED)
+			return POLLIN | POLLRDNORM;
+	}
+
+	return 0;
+}
+
 unsigned int bt_sock_poll(struct file * file, struct socket *sock, poll_table *wait)
 {
 	struct sock *sk = sock->sk;
-	unsigned int mask;
+	unsigned int mask = 0;
 
 	BT_DBG("sock %p, sk %p", sock, sk);
 
 	poll_wait(file, sk->sk_sleep, wait);
-	mask = 0;
+
+	if (sk->sk_state == BT_LISTEN)
+		return bt_sock_listen_poll(sk, wait);
 
 	if (sk->sk_err || !skb_queue_empty(&sk->sk_error_queue))
 		mask |= POLLERR;
@@ -253,16 +272,17 @@
 		mask |= POLLHUP;
 
 	if (!skb_queue_empty(&sk->sk_receive_queue) || 
-			!list_empty(&bt_sk(sk)->accept_q) ||
 			(sk->sk_shutdown & RCV_SHUTDOWN))
 		mask |= POLLIN | POLLRDNORM;
 
 	if (sk->sk_state == BT_CLOSED)
 		mask |= POLLHUP;
 
-	if (sk->sk_state == BT_CONNECT || sk->sk_state == BT_CONNECT2)
+	if (sk->sk_state == BT_CONNECT ||
+			sk->sk_state == BT_CONNECT2 ||
+			sk->sk_state == BT_CONFIG)
 		return mask;
-	
+
 	if (sock_writeable(sk))
 		mask |= POLLOUT | POLLWRNORM | POLLWRBAND;
 	else