Merge branch 'af_unix-remove-spin_lock_nested-and-convert-to-lock_cmp_fn'

Kuniyuki Iwashima says:

====================
af_unix: Remove spin_lock_nested() and convert to lock_cmp_fn.

This series removes spin_lock_nested() in AF_UNIX and instead
defines the locking orders as functions tied to each lock by
lockdep_set_lock_cmp_fn().

When the defined function returns a negative value, lockdep
considers it will not cause deadlock.  (See ->cmp_fn() in
check_deadlock() and check_prev_add().)

When we cannot define the total ordering, we return -1 for
the allowed ordering and otherwise 0 as undefined. [0]

[0]: https://lore.kernel.org/netdev/thzkgbuwuo3knevpipu4rzsh5qgmwhklihypdgziiruabvh46f@uwdkpcfxgloo/

Changes:
  v4:
    * Patch 4
      * Make unix_state_lock_cmp_fn() symmetric.

  v3: https://lore.kernel.org/netdev/20240614200715.93150-1-kuniyu@amazon.com/
    * Patch 3
      * Cache sk->sk_state
      * s/unix_state_lock()/unix_state_unlock()/
    * Patch 8
      * Add embryo -> listener locking order

  v2: https://lore.kernel.org/netdev/20240611222905.34695-1-kuniyu@amazon.com/
   * Patch 1 & 2
      * Use (((l) > (r)) - ((l) < (r))) for comparison

  v1: https://lore.kernel.org/netdev/20240610223501.73191-1-kuniyu@amazon.com/
====================

Link: https://lore.kernel.org/r/20240620205623.60139-1-kuniyu@amazon.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>