Re: [RFC PATCH v5 02/19] af_vsock: separate wait data loop

Jorgen Hansen
2021-02-25T14:25:21Z

> On 18 Feb 2021, at 06:36, Arseny Krasnov <arseny.krasnov@kaspersky.com> wrote:
>
> This moves wait loop for data to dedicated function, because later
> it will be used by SEQPACKET data receive loop.
>
> Signed-off-by: Arseny Krasnov <arseny.krasnov@kaspersky.com>
> ---
> net/vmw_vsock/af_vsock.c | 155 +++++++++++++++++++++------------------
> 1 file changed, 83 insertions(+), 72 deletions(-)
>
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index 656370e11707..6cf7bb977aa1 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -1832,6 +1832,68 @@ static int vsock_connectible_sendmsg(struct socket *sock, struct msghdr *msg,
> return err;
> }
>
> +static int vsock_wait_data(struct sock *sk, struct wait_queue_entry *wait,
> + long timeout,
> + struct vsock_transport_recv_notify_data *recv_data,
> + size_t target)
> +{
> + const struct vsock_transport *transport;
> + struct vsock_sock *vsk;
> + s64 data;
> + int err;
> +
> + vsk = vsock_sk(sk);
> + err = 0;
> + transport = vsk->transport;
> + prepare_to_wait(sk_sleep(sk), wait, TASK_INTERRUPTIBLE);
> +
> + while ((data = vsock_stream_has_data(vsk)) == 0) {

In the original code, the prepare_to_wait() is called for each iteration of the while loop. In this
version, it is only called once. So if we do multiple iterations, the thread would be in the
TASK_RUNNING state, and subsequent schedule_timeout() will return immediately. So
looks like the prepare_to_wait() should be move here, in case we have a spurious wake_up.

> + if (sk->sk_err != 0 ||
> + (sk->sk_shutdown & RCV_SHUTDOWN) ||
> + (vsk->peer_shutdown & SEND_SHUTDOWN)) {
> + break;
> + }
> +
> + /* Don't wait for non-blocking sockets. */
> + if (timeout == 0) {
> + err = -EAGAIN;
> + break;
> + }
> +
> + if (recv_data) {
> + err = transport->notify_recv_pre_block(vsk, target, recv_data);
> + if (err < 0)
> + break;
> + }
> +
> + release_sock(sk);
> + timeout = schedule_timeout(timeout);
> + lock_sock(sk);
> +
> + if (signal_pending(current)) {
> + err = sock_intr_errno(timeout);
> + break;
> + } else if (timeout == 0) {
> + err = -EAGAIN;
> + break;
> + }
> + }
> +
> + finish_wait(sk_sleep(sk), wait);
> +
> + if (err)
> + return err;
> +
> + /* Internal transport error when checking for available
> + * data. XXX This should be changed to a connection
> + * reset in a later change.
> + */
> + if (data < 0)
> + return -ENOMEM;
> +
> + return data;
> +}
> +
> static int
> vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
> int flags)
> @@ -1911,85 +1973,34 @@ vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>
>
> while (1) {
> - s64 ready;
> -
> - prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
> - ready = vsock_stream_has_data(vsk);
> -
> - if (ready == 0) {
> - if (sk->sk_err != 0 ||
> - (sk->sk_shutdown & RCV_SHUTDOWN) ||
> - (vsk->peer_shutdown & SEND_SHUTDOWN)) {
> - finish_wait(sk_sleep(sk), &wait);
> - break;
> - }
> - /* Don't wait for non-blocking sockets. */
> - if (timeout == 0) {
> - err = -EAGAIN;
> - finish_wait(sk_sleep(sk), &wait);
> - break;
> - }
> + ssize_t read;
>
> - err = transport->notify_recv_pre_block(
> - vsk, target, &recv_data);
> - if (err < 0) {
> - finish_wait(sk_sleep(sk), &wait);
> - break;
> - }
> - release_sock(sk);
> - timeout = schedule_timeout(timeout);
> - lock_sock(sk);
> + err = vsock_wait_data(sk, &wait, timeout, &recv_data, target);
> + if (err <= 0)
> + break;
>
> - if (signal_pending(current)) {
> - err = sock_intr_errno(timeout);
> - finish_wait(sk_sleep(sk), &wait);
> - break;
> - } else if (timeout == 0) {
> - err = -EAGAIN;
> - finish_wait(sk_sleep(sk), &wait);
> - break;
> - }
> - } else {
> - ssize_t read;
> -
> - finish_wait(sk_sleep(sk), &wait);
> -
> - if (ready < 0) {
> - /* Invalid queue pair content. XXX This should
> - * be changed to a connection reset in a later
> - * change.
> - */
> -
> - err = -ENOMEM;
> - goto out;
> - }
> -
> - err = transport->notify_recv_pre_dequeue(
> - vsk, target, &recv_data);
> - if (err < 0)
> - break;
> + err = transport->notify_recv_pre_dequeue(vsk, target,
> + &recv_data);
> + if (err < 0)
> + break;
>
> - read = transport->stream_dequeue(
> - vsk, msg,
> - len - copied, flags);
> - if (read < 0) {
> - err = -ENOMEM;
> - break;
> - }
> + read = transport->stream_dequeue(vsk, msg, len - copied, flags);
> + if (read < 0) {
> + err = -ENOMEM;
> + break;
> + }
>
> - copied += read;
> + copied += read;
>
> - err = transport->notify_recv_post_dequeue(
> - vsk, target, read,
> - !(flags & MSG_PEEK), &recv_data);
> - if (err < 0)
> - goto out;
> + err = transport->notify_recv_post_dequeue(vsk, target, read,
> + !(flags & MSG_PEEK), &recv_data);
> + if (err < 0)
> + goto out;
>
> - if (read >= target || flags & MSG_PEEK)
> - break;
> + if (read >= target || flags & MSG_PEEK)
> + break;
>
> - target -= read;
> - }
> + target -= read;
> }
>
> if (sk->sk_err)
> --
> 2.25.1
>