On Thu, May 03, 2012 at 04:33:55PM +0800, Liu ping fan wrote:
> 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
See comment before void __rcu *private_data in vhost.h
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