Re: [RFC PATCH v9 19/19] af_vsock: serialize writes to shared socket

[Arseny Krasnov <arseny.krasnov@kaspersky.com>]

On 13.05.2021 17:01, Stefano Garzarella wrote:
> On Sat, May 08, 2021 at 07:37:35PM +0300, Arseny Krasnov wrote:
>> This add logic, that serializes write access to single socket
>> by multiple threads. It is implemented be adding field with TID
>> of current writer. When writer tries to send something, it checks
>> that field is -1(free), else it sleep in the same way as waiting
>> for free space at peers' side.
>>
>> Signed-off-by: Arseny Krasnov <arseny.krasnov@kaspersky.com>
>> ---
>> include/net/af_vsock.h   |  1 +
>> net/vmw_vsock/af_vsock.c | 10 +++++++++-
>> 2 files changed, 10 insertions(+), 1 deletion(-)
> I think you forgot to move this patch at the beginning of the series.
> It's important because in this way we can backport to stable branches 
> easily.
>
> About the implementation, can't we just add a mutex that we hold until 
> we have sent all the payload?
>
> I need to check other implementations like TCP.
>
>> diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
>> index 1747c0b564ef..413343f18e99 100644
>> --- a/include/net/af_vsock.h
>> +++ b/include/net/af_vsock.h
>> @@ -69,6 +69,7 @@ struct vsock_sock {
>> 	u64 buffer_size;
>> 	u64 buffer_min_size;
>> 	u64 buffer_max_size;
>> +	pid_t tid_owner;
>>
>> 	/* Private to transport. */
>> 	void *trans;
>> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
>> index 7790728465f4..1fb4a1860f6d 100644
>> --- a/net/vmw_vsock/af_vsock.c
>> +++ b/net/vmw_vsock/af_vsock.c
>> @@ -757,6 +757,7 @@ static struct sock *__vsock_create(struct net *net,
>> 	vsk->peer_shutdown = 0;
>> 	INIT_DELAYED_WORK(&vsk->connect_work, vsock_connect_timeout);
>> 	INIT_DELAYED_WORK(&vsk->pending_work, vsock_pending_work);
>> +	vsk->tid_owner = -1;
>>
>> 	psk = parent ? vsock_sk(parent) : NULL;
>> 	if (parent) {
>> @@ -1765,7 +1766,9 @@ static int vsock_connectible_sendmsg(struct socket *sock, struct msghdr *msg,
>> 		ssize_t written;
>>
>> 		add_wait_queue(sk_sleep(sk), &wait);
>> -		while (vsock_stream_has_space(vsk) == 0 &&
>> +		while ((vsock_stream_has_space(vsk) == 0 ||
>> +			(vsk->tid_owner != current->pid &&
>> +			 vsk->tid_owner != -1)) &&
>> 		       sk->sk_err == 0 &&
>> 		       !(sk->sk_shutdown & SEND_SHUTDOWN) &&
>> 		       !(vsk->peer_shutdown & RCV_SHUTDOWN)) {
>> @@ -1796,6 +1799,8 @@ static int vsock_connectible_sendmsg(struct socket *sock, struct msghdr *msg,
>> 				goto out_err;
>> 			}
>> 		}
>> +
>> +		vsk->tid_owner = current->pid;
>> 		remove_wait_queue(sk_sleep(sk), &wait);
>>
>> 		/* These checks occur both as part of and after the loop
>> @@ -1852,7 +1857,10 @@ static int vsock_connectible_sendmsg(struct socket *sock, struct msghdr *msg,
>> 			err = total_written;
>> 	}
>> out:
>> +	vsk->tid_owner = -1;
>> 	release_sock(sk);
>> +	sk->sk_write_space(sk);
>> +
> Is this change related? Can you explain in the commit message why it is 
> needed?
This is "unlocking" of socket
>
>> 	return err;
>> }
>>
>> -- 
>> 2.25.1
>>
>