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

[Jorgen Hansen <jhansen@vmware.com>]

> 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
>