Oh, got it. It is a very interesting implement.
Thanks and regards,
pingfan
On Thu, May 3, 2012 at 4:41 PM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
> 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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