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

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Date:   Thu, 13 May 2021 17:41:21 +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>,
        Norbert Slusarek <nslusarek@....net>,
        Andra Paraschiv <andraprs@...zon.com>,
        Colin Ian King <colin.king@...onical.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 v9 19/19] af_vsock: serialize writes to shared socket

On Thu, May 13, 2021 at 05:48:19PM +0300, Arseny Krasnov wrote:
>
>On 13.05.2021 17:46, Stefano Garzarella wrote:
>> On Thu, May 13, 2021 at 04:01:50PM +0200, 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@...persky.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?
>> Re-thinking, I guess we can't because we have the timeout to deal
>> with...
>Yes, i forgot about why i've implemented it using 'tid_owner' :)

It is not clear to me if we need to do this also for stream.

I think will be better to follow af_inet/af_unix, but I need to check 
their implementation.

Thanks,
Stefano