netlink: rx mmap: notify only when NL_MMAP_STATUS_VALID frame exists

index 7e1610e..8901acd 100644
@@ -576,16 +576,6 @@ netlink_current_frame(const struct netlink_ring *ring,
 	return netlink_lookup_frame(ring, ring->head, status);
 }
 
-static struct nl_mmap_hdr *
-netlink_previous_frame(const struct netlink_ring *ring,
-		       enum nl_mmap_status status)
-{
-	unsigned int prev;
-
-	prev = ring->head ? ring->head - 1 : ring->frame_max;
-	return netlink_lookup_frame(ring, prev, status);
-}
-
 static void netlink_increment_head(struct netlink_ring *ring)
 {
 	ring->head = ring->head != ring->frame_max ? ring->head + 1 : 0;

@@ -606,6 +596,21 @@ static void netlink_forward_ring(struct netlink_ring *ring)
 	} while (ring->head != head);
 }
 
+static bool netlink_has_valid_frame(struct netlink_ring *ring)
+{
+	unsigned int head = ring->head, pos = head;
+	const struct nl_mmap_hdr *hdr;
+
+	do {
+		hdr = __netlink_lookup_frame(ring, pos);
+		if (hdr->nm_status == NL_MMAP_STATUS_VALID)
+			return true;
+		pos = pos != ring->frame_max ? pos + 1 : 0;
+	} while (pos != head);
+
+	return false;
+}
+
 static bool netlink_dump_space(struct netlink_sock *nlk)
 {
 	struct netlink_ring *ring = &nlk->rx_ring;

@@ -653,8 +658,7 @@ static unsigned int netlink_poll(struct file *file, struct socket *sock,
 
 	spin_lock_bh(&sk->sk_receive_queue.lock);
 	if (nlk->rx_ring.pg_vec) {
-		netlink_forward_ring(&nlk->rx_ring);
-		if (!netlink_previous_frame(&nlk->rx_ring, NL_MMAP_STATUS_UNUSED))
+		if (netlink_has_valid_frame(&nlk->rx_ring))
 			mask |= POLLIN | POLLRDNORM;
 	}
 	spin_unlock_bh(&sk->sk_receive_queue.lock);