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Subject: Re: [RFC PATCH v4 02/17] af_vsock: separate wait data loop
To:     Jorgen Hansen <jhansen@vmware.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>,
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        <virtualization@lists.linux-foundation.org>,
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        "oxffffaa@gmail.com" <oxffffaa@gmail.com>
References: <20210207151259.803917-1-arseny.krasnov@kaspersky.com>
 <20210207151451.804498-1-arseny.krasnov@kaspersky.com>
 <4094442C-C2A1-49D6-9901-7F3C73FABFC9@vmware.com>
From:   Arseny Krasnov <arseny.krasnov@kaspersky.com>
Message-ID: <baa11cfd-2f12-fea0-3f5c-015f5d682334@kaspersky.com>
Date:   Tue, 16 Feb 2021 09:58:32 +0300
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On 11.02.2021 18:11, Jorgen Hansen wrote:
>> 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.

May be i can add the following 'if' after while (1) loop:

There was:

if (sk->sk_err)
??? err = -sk->sk->sk_err;
else if (sk->sk_shutdown & RCV_SHUTDOWN)
??? err = 0;
if (copied > 0)
??? err = copied;

Will be:

if (err == 0) {
??? if (sk->sk_err)
??? ??? err = -sk->sk->sk_err;
???? else if (sk->sk_shutdown & RCV_SHUTDOWN)
?? ??? err = 0;

??? if (copied > 0)
??? ??? err = copied;

}

E.g. update 'err' only if it is clear. Don't touch otherwise


>
>> -			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
>>
>