vsock: lookup and setup guest_cid inside vhost_vsock_lock

Multi vsocks may setup the same cid at the same time.
Signed-off-by: Gao feng <omarapazanadi@gmail.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

drivers/vhost/vsock.c

@@ -50,11 +50,10 @@ static u32 vhost_transport_get_local_cid(void)
 	return VHOST_VSOCK_DEFAULT_HOST_CID;
 }
 
-static struct vhost_vsock *vhost_vsock_get(u32 guest_cid)
+static struct vhost_vsock *__vhost_vsock_get(u32 guest_cid)
 {
 	struct vhost_vsock *vsock;
 
-	spin_lock_bh(&vhost_vsock_lock);
 	list_for_each_entry(vsock, &vhost_vsock_list, list) {
 		u32 other_cid = vsock->guest_cid;
 
@@ -63,15 +62,24 @@ static struct vhost_vsock *vhost_vsock_get(u32 guest_cid)
 			continue;
 
 		if (other_cid == guest_cid) {
-			spin_unlock_bh(&vhost_vsock_lock);
 			return vsock;
 		}
 	}
-	spin_unlock_bh(&vhost_vsock_lock);
 
 	return NULL;
 }
 
+static struct vhost_vsock *vhost_vsock_get(u32 guest_cid)
+{
+	struct vhost_vsock *vsock;
+
+	spin_lock_bh(&vhost_vsock_lock);
+	vsock = __vhost_vsock_get(guest_cid);
+	spin_unlock_bh(&vhost_vsock_lock);
+
+	return vsock;
+}
+
 static void
 vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
 			    struct vhost_virtqueue *vq)
@@ -559,11 +567,12 @@ static int vhost_vsock_set_cid(struct vhost_vsock *vsock, u64 guest_cid)
 		return -EINVAL;
 
 	/* Refuse if CID is already in use */
-	other = vhost_vsock_get(guest_cid);
-	if (other && other != vsock)
-		return -EADDRINUSE;
-
 	spin_lock_bh(&vhost_vsock_lock);
+	other = __vhost_vsock_get(guest_cid);
+	if (other && other != vsock) {
+		spin_unlock_bh(&vhost_vsock_lock);
+		return -EADDRINUSE;
+	}
 	vsock->guest_cid = guest_cid;
 	spin_unlock_bh(&vhost_vsock_lock);