vhost-net: is there a race for sock in handle_tx/rx?

[Liu ping fan]

Hi,

During reading the vhost-net code, I find the following,

static void handle_tx(struct vhost_net *net)
{
        struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_TX];
        unsigned out, in, s;
        int head;
        struct msghdr msg = {
                .msg_name = NULL,
                .msg_namelen = 0,
                .msg_control = NULL,
                .msg_controllen = 0,
                .msg_iov = vq->iov,
                .msg_flags = MSG_DONTWAIT,
        };
        size_t len, total_len = 0;
        int err, wmem;
        size_t hdr_size;
        struct socket *sock;
        struct vhost_ubuf_ref *uninitialized_var(ubufs);
        bool zcopy;

        /* TODO: check that we are running from vhost_worker? */
        sock = rcu_dereference_check(vq->private_data, 1);
        if (!sock)
                return;

           --------------------------------> Qemu calls
vhost_net_set_backend() to set a new backend fd, and close
@oldsock->file. And  sock->file refcnt==0.

                                              Can vhost_worker prevent
itself from such situation? And how?

        wmem = atomic_read(&sock->sk->sk_wmem_alloc);
       .........................................................................

Is it a race?

Thanks and regards,
pingfan
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