vhost: rcu annotation fixup

When built with rcu checks enabled, vhost triggers
bogus warnings as vhost features are read without
dev->mutex sometimes, and private pointer is read
with our kind of rcu where work serves as a
read side critical section.

Fixing it properly is not trivial.
Disable the warnings by stubbing out the checks for now.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vhost/net.c

@@ -128,8 +128,7 @@ static void handle_tx(struct vhost_net *net)
 	size_t hdr_size;
 	struct socket *sock;
 
-	/* TODO: check that we are running from vhost_worker?
-	 * Not sure it's worth it, it's straight-forward enough. */
+	/* TODO: check that we are running from vhost_worker? */
 	sock = rcu_dereference_check(vq->private_data, 1);
 	if (!sock)
 		return;
@@ -306,7 +305,8 @@ static void handle_rx_big(struct vhost_net *net)
 	size_t len, total_len = 0;
 	int err;
 	size_t hdr_size;
-	struct socket *sock = rcu_dereference(vq->private_data);
+	/* TODO: check that we are running from vhost_worker? */
+	struct socket *sock = rcu_dereference_check(vq->private_data, 1);
 	if (!sock || skb_queue_empty(&sock->sk->sk_receive_queue))
 		return;
 
@@ -415,7 +415,8 @@ static void handle_rx_mergeable(struct vhost_net *net)
 	int err, headcount;
 	size_t vhost_hlen, sock_hlen;
 	size_t vhost_len, sock_len;
-	struct socket *sock = rcu_dereference(vq->private_data);
+	/* TODO: check that we are running from vhost_worker? */
+	struct socket *sock = rcu_dereference_check(vq->private_data, 1);
 	if (!sock || skb_queue_empty(&sock->sk->sk_receive_queue))
 		return;
 

drivers/vhost/vhost.h

@@ -173,9 +173,9 @@ static inline int vhost_has_feature(struct vhost_dev *dev, int bit)
 {
 	unsigned acked_features;
 
-	acked_features =
-		rcu_dereference_index_check(dev->acked_features,
-					    lockdep_is_held(&dev->mutex));
+	/* TODO: check that we are running from vhost_worker or dev mutex is
+	 * held? */
+	acked_features = rcu_dereference_index_check(dev->acked_features, 1);
 	return acked_features & (1 << bit);
 }