[PATCH mptcp-next v3 0/3] send() fails with EAGAIN in blocking IO mode #487

[Geliang Tang <geliang@kernel.org>]

From: Geliang Tang <tanggeliang@kylinos.cn>

Good news! I finally solved the unstable issue of MPTCP BPF sched selftests
I reported a year ago, #487 "send() fails with EAGAIN in blocking IO mode".

The fix is simple, it can be solved by explicitly setting SO_SNDBUF
sockopt, but be sure not to set SO_RCVBUF at the same time
(see sk->sk_userlocks & SOCK_RCVBUF_LOCK in mptcp_rcv_space_adjust()).

With this fix, BPF sched selftests are now very stable, I run loop testing
using mptcp-upstream-virtme-docker (run_loop run_bpftest_all), and can run
it normally for hundreds of times without error:


	=== Attempt: 465 (Thu, 29 May 2025 04:04:09 +0000) ===

BPF Test: test_progs -t mptcp
TAP version 13
1..1
# #198/1   mptcp/base:OK
# #198/2   mptcp/mptcpify:OK
# #198/3   mptcp/subflow:OK
# #198/4   mptcp/iters_subflow:OK
# #198/5   mptcp/default:OK
# #198/6   mptcp/first:OK
# #198/7   mptcp/bkup:OK
# #198/8   mptcp/rr:OK
# #198/9   mptcp/red:OK
# #198/10  mptcp/burst:OK
# #198     mptcp:OK
# Summary: 1/10 PASSED, 0 SKIPPED, 0 FAILED
ok 1 test: bpftest_test_progs_mptcp
# time=3
BPF Test: test_progs-cpuv4 -t mptcp
TAP version 13
1..1
# #198/1   mptcp/base:OK
# #198/2   mptcp/mptcpify:OK
# #198/3   mptcp/subflow:OK
# #198/4   mptcp/iters_subflow:OK
# #198/5   mptcp/default:OK
# #198/6   mptcp/first:OK
# #198/7   mptcp/bkup:OK
# #198/8   mptcp/rr:OK
# #198/9   mptcp/red:OK
# #198/10  mptcp/burst:OK
# #198     mptcp:OK
# Summary: 1/10 PASSED, 0 SKIPPED, 0 FAILED
ok 1 test: bpftest_test_progs-cpuv4_mptcp
# time=4
BPF Test: test_progs-no_alu32 -t mptcp
TAP version 13
1..1
# #198/1   mptcp/base:OK
# #198/2   mptcp/mptcpify:OK
# #198/3   mptcp/subflow:OK
# #198/4   mptcp/iters_subflow:OK
# #198/5   mptcp/default:OK
# #198/6   mptcp/first:OK
# #198/7   mptcp/bkup:OK
# #198/8   mptcp/rr:OK
# #198/9   mptcp/red:OK
# #198/10  mptcp/burst:OK
# #198     mptcp:OK
# Summary: 1/10 PASSED, 0 SKIPPED, 0 FAILED
ok 1 test: bpftest_test_progs-no_alu32_mptcp
# time=3

	=== Attempt: 466 (Thu, 29 May 2025 04:04:19 +0000) ===


This set also invalidates the following set named "add io thread mode
tests":
https://patchwork.kernel.org/project/mptcp/cover/cover.1722502941.git.tanggeliang@kylinos.cn/

v2:
 - mptcp: fix the default value of scaling_ratio
 https://patchwork.kernel.org/project/mptcp/patch/0ccc1c26d27d6ee7be22806a97983d37c6ca548c.1715053270.git.tanggeliang@kylinos.cn/

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/487

Geliang Tang (3):
  selftests/bpf: Add sndbuf for send_recv_data
  Squash to "selftests/bpf: Add bpf scheduler test"
  DO-NOT-MERGE: selftests/bpf: Increase total_bytes of bpf sched tests

 tools/testing/selftests/bpf/network_helpers.c | 20 ++++++++++++++++++-
 tools/testing/selftests/bpf/network_helpers.h |  2 +-
 .../selftests/bpf/prog_tests/bpf_qdisc.c      |  2 +-
 .../selftests/bpf/prog_tests/bpf_tcp_ca.c     |  4 ++--
 .../testing/selftests/bpf/prog_tests/mptcp.c  | 13 ++++++++++--
 5 files changed, 34 insertions(+), 7 deletions(-)

-- 
2.43.0