Re: [PATCHv7 3/3] vhost_net: a kernel-level virtio server

Eric Dumazet
2009-11-03T18:05:44Z

Michael S. Tsirkin a écrit :
> +static void handle_tx(struct vhost_net *net)
> +{
> + struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_TX];
> + unsigned head, out, in, s;
> + 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 = rcu_dereference(vq->private_data);
> + if (!sock)
> + return;
> +
> + wmem = atomic_read(&sock->sk->sk_wmem_alloc);
> + if (wmem >= sock->sk->sk_sndbuf)
> + return;
> +
> + use_mm(net->dev.mm);
> + mutex_lock(&vq->mutex);
> + vhost_no_notify(vq);
> +

using rcu_dereference() and mutex_lock() at the same time seems wrong, I suspect
that your use of RCU is not correct.

1) rcu_dereference() should be done inside a read_rcu_lock() section, and
we are not allowed to sleep in such a section.
(Quoting Documentation/RCU/whatisRCU.txt :
It is illegal to block while in an RCU read-side critical section, )

2) mutex_lock() can sleep (ie block)