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

[Arseniy Krasnov]

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@xxxxxxxxxxxxxx/
> 
> 
> Patchset:
> 
> Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>

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

> 
> 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@xxxxxxxxxxxxxxxxx/
>> Link to v2:
>> https://lore.kernel.org/netdev/20231119204922.2251912-1-avkrasnov@xxxxxxxxxxxxxxxxx/
>> Link to v3:
>> https://lore.kernel.org/netdev/20231122180510.2297075-1-avkrasnov@xxxxxxxxxxxxxxxxx/
>> Link to v4:
>> https://lore.kernel.org/netdev/20231129212519.2938875-1-avkrasnov@xxxxxxxxxxxxxxxxx/
>> Link to v5:
>> https://lore.kernel.org/netdev/20231130130840.253733-1-avkrasnov@xxxxxxxxxxxxxxxxx/
>> Link to v6:
>> https://lore.kernel.org/netdev/20231205064806.2851305-1-avkrasnov@xxxxxxxxxxxxxxxxx/
>> Link to v7:
>> https://lore.kernel.org/netdev/20231206211849.2707151-1-avkrasnov@xxxxxxxxxxxxxxxxx/
>>
>> 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
>