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

Stefano Garzarella
2021-04-21T09:39:01Z

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.

Thanks,
Stefano

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