netdev - [RFC PATCH v3 net-next 0/4] txhash: Make hash rethink configurable

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Message-Id: <20211206191111.14376-1-hmukos@yandex-team.ru>
Date:   Mon,  6 Dec 2021 22:11:07 +0300
From:   Akhmat Karakotov <hmukos@...dex-team.ru>
To:     netdev@...r.kernel.org
Cc:     hmukos@...dex-team.ru, edumazet@...gle.com, eric.dumazet@...il.com,
        mitradir@...dex-team.ru, tom@...bertland.com, zeil@...dex-team.ru
Subject: [RFC PATCH v3 net-next 0/4] txhash: Make hash rethink configurable

As it was shown in the report by Alexander Azimov, hash rethink at the
client-side may lead to connection timeout toward stateful anycast
services. Tom Herbert created a patchset to address this issue by applying
hash rethink only after a negative routing event (3RTOs) [1]. This change
also affects server-side behavior, which we found undesirable. This
patchset changes defaults in a way to make them safe: hash rethink at the
client-side is disabled and enabled at the server-side upon each RTO
event or in case of duplicate acknowledgments.

This patchset provides two options to change default behaviour. The hash
rethink may be disabled at the server-side by the new sysctl option.
Changes in the sysctl option don't affect default behavior at the
client-side.

Hash rethink can also be enabled/disabled with socket option or bpf
syscalls which ovewrite both default and sysctl settings. This socket
option is available on both client and server-side. This should provide
mechanics to enable hash rethink inside administrative domain, such as DC,
where hash rethink at the client-side can be desirable.

[1] https://lore.kernel.org/netdev/20210809185314.38187-1-tom@herbertland.com/

v2:
	- Changed sysctl default to ENABLED in all patches. Reduced sysctl
	  and socket option size to u8. Fixed netns bug reported by kernel
	  test robot.

v3:
	- Fixed bug with bad u8 comparison. Moved sk->txrehash to use less
	  bytes in struct. Added WRITE_ONCE() in setsockopt in and
	  READ_ONCE() in tcp_rtx_synack.

Akhmat Karakotov (4):
  txhash: Make rethinking txhash behavior configurable via sysctl
  txhash: Add socket option to control TX hash rethink behavior
  bpf: Add SO_TXREHASH setsockopt
  tcp: change SYN ACK retransmit behaviour to account for rehash

 arch/alpha/include/uapi/asm/socket.h  |  2 ++
 arch/mips/include/uapi/asm/socket.h   |  2 ++
 arch/parisc/include/uapi/asm/socket.h |  2 ++
 arch/sparc/include/uapi/asm/socket.h  |  2 ++
 include/net/netns/core.h              |  1 +
 include/net/sock.h                    | 28 ++++++++++++++-------------
 include/uapi/asm-generic/socket.h     |  2 ++
 include/uapi/linux/socket.h           |  4 ++++
 net/core/filter.c                     | 10 ++++++++++
 net/core/net_namespace.c              |  2 ++
 net/core/sock.c                       | 14 ++++++++++++++
 net/core/sysctl_net_core.c            | 14 ++++++++++++--
 net/ipv4/inet_connection_sock.c       |  3 +++
 net/ipv4/tcp_output.c                 |  4 +++-
 14 files changed, 74 insertions(+), 16 deletions(-)

-- 
2.17.1