Re: [RFC PATCH v4 02/17] af_vsock: separate wait data loop

From: Jorgen Hansen <jhansen@vmware.com>
To: Arseny Krasnov <arseny.krasnov@kaspersky.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>,
	Stefano Garzarella <sgarzare@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Jason Wang <jasowang@redhat.com>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Colin Ian King <colin.king@canonical.com>,
	Andra Paraschiv <andraprs@amazon.com>,
	Alexander Popov <alex.popov@linux.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"virtualization@lists.linux-foundation.org" 
	<virtualization@lists.linux-foundation.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"stsp2@yandex.ru" <stsp2@yandex.ru>,
	"oxffffaa@gmail.com" <oxffffaa@gmail.com>
Subject: Re: [RFC PATCH v4 02/17] af_vsock: separate wait data loop
Date: Thu, 11 Feb 2021 15:11:07 +0000	[thread overview]
Message-ID: <4094442C-C2A1-49D6-9901-7F3C73FABFC9@vmware.com> (raw)
In-Reply-To: <20210207151451.804498-1-arseny.krasnov@kaspersky.com>

> On 7 Feb 2021, at 16:14, 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 | 158 +++++++++++++++++++++------------------
> 1 file changed, 86 insertions(+), 72 deletions(-)
> 
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index f4fabec50650..38927695786f 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -1833,6 +1833,71 @@ 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) {
> +		if (sk->sk_err != 0 ||
> +		    (sk->sk_shutdown & RCV_SHUTDOWN) ||
> +		    (vsk->peer_shutdown & SEND_SHUTDOWN)) {
> +			goto out;
> +		}
> +
> +		/* Don't wait for non-blocking sockets. */
> +		if (timeout == 0) {
> +			err = -EAGAIN;
> +			goto out;
> +		}
> +
> +		if (recv_data) {
> +			err = transport->notify_recv_pre_block(vsk, target, recv_data);
> +			if (err < 0)
> +				goto out;
> +		}
> +
> +		release_sock(sk);
> +		timeout = schedule_timeout(timeout);
> +		lock_sock(sk);
> +
> +		if (signal_pending(current)) {
> +			err = sock_intr_errno(timeout);
> +			goto out;
> +		} else if (timeout == 0) {
> +			err = -EAGAIN;
> +			goto out;
> +		}
> +	}
> +
> +	finish_wait(sk_sleep(sk), wait);
> +
> +	/* Invalid queue pair content. XXX This should
> +	 * be changed to a connection reset in a later
> +	 * change.
> +	 */

Since you are here, could you update this comment to something like:

/* 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;
> +
> +	/* Have some data, return. */
> +	if (data)
> +		return data;
> +
> +out:
> +	finish_wait(sk_sleep(sk), wait);
> +	return err;
> +}

I agree with Stefanos suggestion to get rid of the out: part  and just have the single finish_wait().

> +
> static int
> vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
> 			  int flags)
> @@ -1912,85 +1977,34 @@ vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
> 
> 
> 	while (1) {
> -		s64 ready;
> +		ssize_t read;
> 
> -		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;
> -			}
> -
> -			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);
> -
> -			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;
> +		err = vsock_wait_data(sk, &wait, timeout, &recv_data, target);
> +		if (err <= 0)
> +			break;

There is a small change in the behaviour here if vsock_stream_has_data(vsk)
returned something < 0. Since you just do a break, the err value can be updated
if there is an sk->sk_err, a receive shutdown has been performed or data has
already been copied. That should be ok, though.

> -			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
> 