Re: [RFC PATCH v8 19/19] af_vsock: serialize writes to shared socket

Arseny Krasnov
2021-04-21T15:02:40Z

On 21.04.2021 12:38, Stefano Garzarella wrote:
> On Wed, Apr 14, 2021 at 01:51:17PM +0300, Arseny Krasnov wrote:
>> On 13.04.2021 15:47, 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.
>>>
>>> This implementation is PoC and not related to SEQPACKET close, so
>>> i've placed it after whole patchset.
>>>
>>> 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(-)
>>>
>>> diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
>>> index 53d3f33dbdbf..786df80b9fc3 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 54bee7e643f4..d00f8c07a9d3 100644
>>> --- a/net/vmw_vsock/af_vsock.c
>>> +++ b/net/vmw_vsock/af_vsock.c
>>> @@ -1765,7 +1765,9 @@ 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 +1798,8 @@ 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 +1856,10 @@ 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);
>>> +
>>> return err;
>>> }
>>>
>>> @@ -2199,6 +2206,7 @@ static int vsock_create(struct net *net, struct socket *sock,
>>> return -ENOMEM;
>>>
>>> vsk = vsock_sk(sk);
>>> + vsk->tid_owner = -1;
>> This must be moved to '__vsock_create()'
> Okay, I'll review the next version.
>
> In order to backport this fix to stable branches I think is better to
> move at the beginning of this series or even out as a separate patch.

Ok, i'll put it as first patch of patchset. I don't like to prepare it as

separate patch, because SEQPACKET will use this fix.

>
> Thanks,
> Stefano
>
>>> if (sock->type == SOCK_DGRAM) {
>>> ret = vsock_assign_transport(vsk, NULL);
>