[PATCH bpf-next v3 0/5] tcp: increase flexibility of EBPF congestion control initialization

[Neal Cardwell <ncardwell.kernel@gmail.com>]

From: Neal Cardwell <ncardwell@google.com>

This patch series reorganizes TCP congestion control initialization so that if
EBPF code called by tcp_init_transfer() sets the congestion control algorithm
by calling setsockopt(TCP_CONGESTION) then the TCP stack initializes the
congestion control module immediately, instead of having tcp_init_transfer()
later initialize the congestion control module.

This increases flexibility for the EBPF code that runs at connection
establishment time, and simplifies the code.

This has the following benefits:

(1) This allows CC module customizations made by the EBPF called in
    tcp_init_transfer() to persist, and not be wiped out by a later
    call to tcp_init_congestion_control() in tcp_init_transfer().

(2) Does not flip the order of EBPF and CC init, to avoid causing bugs
    for existing code upstream that depends on the current order.

(3) Does not cause 2 initializations for for CC in the case where the
    EBPF called in tcp_init_transfer() wants to set the CC to a new CC
    algorithm.

(4) Allows follow-on simplifications to the code in net/core/filter.c
    and net/ipv4/tcp_cong.c, which currently both have some complexity
    to special-case CC initialization to avoid double CC
    initialization if EBPF sets the CC.

changes in v2:

o rebase onto bpf-next

o add another follow-on simplification suggested by Martin KaFai Lau:
   "tcp: simplify tcp_set_congestion_control() load=false case"

changes in v3:

o no change in commits

o resent patch series from @gmail.com, since mail from ncardwell@google.com
  stopped being accepted at netdev@vger.kernel.org mid-way through processing
  the v2 patch series (between patches 2 and 3), confusing patchwork about
  which patches belonged to the v2 patch series

Neal Cardwell (5):
  tcp: only init congestion control if not initialized already
  tcp: simplify EBPF TCP_CONGESTION to always init CC
  tcp: simplify tcp_set_congestion_control(): always reinitialize
  tcp: simplify _bpf_setsockopt(): remove flags argument
  tcp: simplify tcp_set_congestion_control() load=false case

 include/net/inet_connection_sock.h |  3 ++-
 include/net/tcp.h                  |  2 +-
 net/core/filter.c                  | 18 ++++--------------
 net/ipv4/tcp.c                     |  3 ++-
 net/ipv4/tcp_cong.c                | 27 +++++++--------------------
 net/ipv4/tcp_input.c               |  4 +++-
 6 files changed, 19 insertions(+), 38 deletions(-)

-- 
2.28.0.618.gf4bc123cb7-goog