[PATCH mptcp-next v4 0/3] add distinct lockdep class for MPTCP sockets

[Geliang Tang <geliang@kernel.org>]

From: Geliang Tang <tanggeliang@kylinos.cn>

The mptcp_nvme.sh selftest reports lockdep "possible recursive locking"
warnings when running NVMe over MPTCP. The issue occurs because MPTCP
sockets and their subflows share the same k-sk_lock-AF_INET lockdep class,
causing lockdep to flag false warnings in paths that hold the MPTCP socket
lock and then lock a subflow (setsockopt, connect, bind, worker send-ack).

This series fixes the issue by giving MPTCP sockets their own distinct
lockdep class (sk_lock-AF_INET-MPTCP for IPv4, sk_lock-AF_INET6-MPTCP for
IPv6), similar to how nvme-tcp handles it. This approach is more efficient
than reclassifying each subflow individually, properly supports IPv6, and
follows existing kernel patterns.

A KUnit test is included to verify the fix works correctly.

v4:
 - Include existing patch to propagate sk_reuse and sk_reuseport settings
   from MPTCP socket to subflows, and fix unconditional sk_bound_dev_if
   override in __mptcp_subflow_connect()
 - Enhanced KUnit test to cover SO_BINDTODEVICE and SO_BINDTOIFINDEX
   socket options in addition to SO_REUSEADDR
 - Refactored sockopt test into helper functions (mptcp_test_reuseaddr,
   mptcp_test_bindtodevice, mptcp_test_bindtoifindex) for better
   maintainability
 - Added proper socket cleanup using kunit_add_action_or_reset() to
   prevent resource leaks on test failures
 - Added READ_ONCE annotation for lockless access to msk->first
 - Added period to Kconfig help text

v3:
 - Assign separate lock classes for kernel and user MPTCP sockets to
   prevent lockdep from conflating their usage patterns (kernel sockets
   may nest with fs/storage locks, user sockets record mmap_lock
   dependencies through page faults)
 - Call mptcp_reclassify_socket() from mptcp_init_sock() for active sockets
   and from mptcp_sk_clone_init() before bh_lock_sock() for passive sockets
 - Remove duplicate lock reclassification from pm_kernel.c (PM listener
   sockets are now reclassified through mptcp_init_sock() path)
 - Enhanced KUnit test to cover both IPv4/IPv6 and active/passive sockets,
   with direct lockdep key comparison when CONFIG_PROVE_LOCKING is enabled
 - Update Kconfig help text to mention sockopt tests
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1792378794.git.tanggeliang@kylinos.cn/

v2:
 - Move reclassification to __mptcp_init_sock() to cover cloned sockets,
   as Matt suggested
 - Extract mptcp_reclassify_socket() helper for reuse in PM listener socket
   creation
 - Remove #ifdef CONFIG_DEBUG_LOCK_ALLOC wrapper as suggested by Matt
 - Update lock class names to msk_lock-AF_INET/msk_lock-AF_INET6
 - Note: checkpatch.pl warns about line length > 80 columns in pm_kernel.c,
   but kept for consistency with existing code style
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1792114102.git.tanggeliang@kylinos.cn/

v1:
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1792060837.git.tanggeliang@kylinos.cn/

Geliang Tang (3):
  mptcp: give MPTCP sockets a distinct lockdep class
  mptcp: inherit sk_reuse and fix dev bind override
  mptcp: kunit: add sockopt test

 net/mptcp/Kconfig        |   2 +-
 net/mptcp/Makefile       |   4 +-
 net/mptcp/pm_kernel.c    |  16 ----
 net/mptcp/protocol.c     |  37 +++++++-
 net/mptcp/sockopt.c      |   5 ++
 net/mptcp/sockopt_test.c | 184 +++++++++++++++++++++++++++++++++++++++
 net/mptcp/subflow.c      |   4 +-
 7 files changed, 232 insertions(+), 20 deletions(-)
 create mode 100644 net/mptcp/sockopt_test.c

-- 
2.55.0