linux-kernel - Re: [PATCH net-next v8 0/4] send credit update during setting SO

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Date:   Tue, 12 Dec 2023 20:43:07 +0300
From:   Arseniy Krasnov <avkrasnov@...utedevices.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Bobby Eshleman <bobby.eshleman@...edance.com>,
        <kvm@...r.kernel.org>, <virtualization@...ts.linux-foundation.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kernel@...rdevices.ru>, <oxffffaa@...il.com>
Subject: Re: [PATCH net-next v8 0/4] send credit update during setting
 SO_RCVLOWAT



On 12.12.2023 19:12, Michael S. Tsirkin wrote:
> On Tue, Dec 12, 2023 at 06:59:03PM +0300, Arseniy Krasnov wrote:
>>
>>
>> On 12.12.2023 18:54, Michael S. Tsirkin wrote:
>>> On Tue, Dec 12, 2023 at 12:16:54AM +0300, Arseniy Krasnov wrote:
>>>> Hello,
>>>>
>>>>                                DESCRIPTION
>>>>
>>>> This patchset fixes old problem with hungup of both rx/tx sides and adds
>>>> test for it. This happens due to non-default SO_RCVLOWAT value and
>>>> deferred credit update in virtio/vsock. Link to previous old patchset:
>>>> https://lore.kernel.org/netdev/39b2e9fd-601b-189d-39a9-914e5574524c@sberdevices.ru/
>>>
>>>
>>> Patchset:
>>>
>>> Acked-by: Michael S. Tsirkin <mst@...hat.com>
>>
>> Thanks!
>>
>>>
>>>
>>> But I worry whether we actually need 3/8 in net not in net-next.
>>
>> Because of "Fixes" tag ? I think this problem is not critical and reproducible
>> only in special cases, but i'm not familiar with netdev process so good, so I don't
>> have strong opinion. I guess @Stefano knows better.
>>
>> Thanks, Arseniy
> 
> Fixes means "if you have that other commit then you need this commit
> too". I think as a minimum you need to rearrange patches to make the
> fix go in first. We don't want a regression followed by a fix.

I see, ok, @Stefano WDYT? I think rearrange doesn't break anything, because this
patch fixes problem that is not related with the new patches from this patchset.

Thanks, Arseniy

> 
>>>
>>> Thanks!
>>>
>>>> Here is what happens step by step:
>>>>
>>>>                                   TEST
>>>>
>>>>                             INITIAL CONDITIONS
>>>>
>>>> 1) Vsock buffer size is 128KB.
>>>> 2) Maximum packet size is also 64KB as defined in header (yes it is
>>>>    hardcoded, just to remind about that value).
>>>> 3) SO_RCVLOWAT is default, e.g. 1 byte.
>>>>
>>>>
>>>>                                  STEPS
>>>>
>>>>             SENDER                              RECEIVER
>>>> 1) sends 128KB + 1 byte in a
>>>>    single buffer. 128KB will
>>>>    be sent, but for 1 byte
>>>>    sender will wait for free
>>>>    space at peer. Sender goes
>>>>    to sleep.
>>>>
>>>>
>>>> 2)                                     reads 64KB, credit update not sent
>>>> 3)                                     sets SO_RCVLOWAT to 64KB + 1
>>>> 4)                                     poll() -> wait forever, there is
>>>>                                        only 64KB available to read.
>>>>
>>>> So in step 4) receiver also goes to sleep, waiting for enough data or
>>>> connection shutdown message from the sender. Idea to fix it is that rx
>>>> kicks tx side to continue transmission (and may be close connection)
>>>> when rx changes number of bytes to be woken up (e.g. SO_RCVLOWAT) and
>>>> this value is bigger than number of available bytes to read.
>>>>
>>>> I've added small test for this, but not sure as it uses hardcoded value
>>>> for maximum packet length, this value is defined in kernel header and
>>>> used to control deferred credit update. And as this is not available to
>>>> userspace, I can't control test parameters correctly (if one day this
>>>> define will be changed - test may become useless). 
>>>>
>>>> Head for this patchset is:
>>>> https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=021b0c952f226236f2edf89c737efb9a28d1422d
>>>>
>>>> Link to v1:
>>>> https://lore.kernel.org/netdev/20231108072004.1045669-1-avkrasnov@salutedevices.com/
>>>> Link to v2:
>>>> https://lore.kernel.org/netdev/20231119204922.2251912-1-avkrasnov@salutedevices.com/
>>>> Link to v3:
>>>> https://lore.kernel.org/netdev/20231122180510.2297075-1-avkrasnov@salutedevices.com/
>>>> Link to v4:
>>>> https://lore.kernel.org/netdev/20231129212519.2938875-1-avkrasnov@salutedevices.com/
>>>> Link to v5:
>>>> https://lore.kernel.org/netdev/20231130130840.253733-1-avkrasnov@salutedevices.com/
>>>> Link to v6:
>>>> https://lore.kernel.org/netdev/20231205064806.2851305-1-avkrasnov@salutedevices.com/
>>>> Link to v7:
>>>> https://lore.kernel.org/netdev/20231206211849.2707151-1-avkrasnov@salutedevices.com/
>>>>
>>>> Changelog:
>>>> v1 -> v2:
>>>>  * Patchset rebased and tested on new HEAD of net-next (see hash above).
>>>>  * New patch is added as 0001 - it removes return from SO_RCVLOWAT set
>>>>    callback in 'af_vsock.c' when transport callback is set - with that
>>>>    we can set 'sk_rcvlowat' only once in 'af_vsock.c' and in future do
>>>>    not copy-paste it to every transport. It was discussed in v1.
>>>>  * See per-patch changelog after ---.
>>>> v2 -> v3:
>>>>  * See changelog after --- in 0003 only (0001 and 0002 still same).
>>>> v3 -> v4:
>>>>  * Patchset rebased and tested on new HEAD of net-next (see hash above).
>>>>  * See per-patch changelog after ---.
>>>> v4 -> v5:
>>>>  * Change patchset tag 'RFC' -> 'net-next'.
>>>>  * See per-patch changelog after ---.
>>>> v5 -> v6:
>>>>  * New patch 0003 which sends credit update during reading bytes from
>>>>    socket.
>>>>  * See per-patch changelog after ---.
>>>> v6 -> v7:
>>>>  * Patchset rebased and tested on new HEAD of net-next (see hash above).
>>>>  * See per-patch changelog after ---.
>>>> v7 -> v8:
>>>>  * See per-patch changelog after ---.
>>>>
>>>> Arseniy Krasnov (4):
>>>>   vsock: update SO_RCVLOWAT setting callback
>>>>   virtio/vsock: send credit update during setting SO_RCVLOWAT
>>>>   virtio/vsock: fix logic which reduces credit update messages
>>>>   vsock/test: two tests to check credit update logic
>>>>
>>>>  drivers/vhost/vsock.c                   |   1 +
>>>>  include/linux/virtio_vsock.h            |   1 +
>>>>  include/net/af_vsock.h                  |   2 +-
>>>>  net/vmw_vsock/af_vsock.c                |   9 +-
>>>>  net/vmw_vsock/hyperv_transport.c        |   4 +-
>>>>  net/vmw_vsock/virtio_transport.c        |   1 +
>>>>  net/vmw_vsock/virtio_transport_common.c |  43 +++++-
>>>>  net/vmw_vsock/vsock_loopback.c          |   1 +
>>>>  tools/testing/vsock/vsock_test.c        | 175 ++++++++++++++++++++++++
>>>>  9 files changed, 229 insertions(+), 8 deletions(-)
>>>>
>>>> -- 
>>>> 2.25.1
>>>
>