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

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Date:   Wed, 21 Apr 2021 11:38:51 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Arseny Krasnov <arseny.krasnov@...persky.com>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jorgen Hansen <jhansen@...are.com>,
        Colin Ian King <colin.king@...onical.com>,
        Norbert Slusarek <nslusarek@....net>,
        Andra Paraschiv <andraprs@...zon.com>,
        Jeff Vander Stoep <jeffv@...gle.com>,
        Alexander Popov <alex.popov@...ux.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stsp2@...dex.ru" <stsp2@...dex.ru>,
        "oxffffaa@...il.com" <oxffffaa@...il.com>
Subject: Re: [RFC PATCH v8 19/19] af_vsock: serialize writes to shared socket

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@...persky.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);
>