Merge branch 'neighbour-namespacify-arp_tbl-and-nd_tbl'

Kuniyuki Iwashima says:

====================
neighbour: Namespacify arp_tbl and nd_tbl.

The neighbour subsystem is almost ready to drop RTNL.

However, the control paths are serialised by the global
per-table lock.

This series converts arp_tbl and nd_tbl to per-netns table.

With the series, /proc/sys/net/ipv{4,6}/neigh/default/ can
be configured per netns, which was only configurable in
init_net.

To avoid potential regression, all the settings are inherited
from init_net by default, and this behaviour is controlled by
a new sysctl knob, net.core.neigh_inherit_init_net:

  # sysctl net.core.neigh_inherit_init_net
  net.core.neigh_inherit_init_net = 1
  # sysctl net.ipv4.neigh.default.gc_thresh1
  net.ipv4.neigh.default.gc_thresh1 = 128
  # sysctl net.ipv4.neigh.default.gc_thresh1=129
  net.ipv4.neigh.default.gc_thresh1 = 129
  # unshare -n sysctl net.ipv4.neigh.default.gc_thresh1
  net.ipv4.neigh.default.gc_thresh1 = 129

If it is turned off, all settings are reset in the new netns:

  # sysctl net.core.neigh_inherit_init_net=0
  net.core.neigh_inherit_init_net = 0
  # unshare -n sysctl net.ipv4.neigh.default.gc_thresh1
  net.ipv4.neigh.default.gc_thresh1 = 128

Series overview:

  Patch 1 deflakes test_neigh.sh.

  Patch 2 ~ 3 are misc cleanup.

  Patch 4 ~ 7 store arp_tbl/nd_tbl to net->neigh_tables[] and
  remove the global neigh_tables[].

  Patch 8 ~ 9 replace the direct access to arp_tbl/nd_tbl to
  net->neigh_tables[] using new helpers.

  Patch 10 ~ 12 finally replace the global table with per-netns
  table.

  Patch 13 ~ 14 clean up unnecessary net_eq().

  Patch 15 updates test_neigh.sh.

Note that some buggy drivers access nd_tbl without checking
disable_ipv6_mod, so nd_tbl's extern definition is still left.
====================

Link: https://patch.msgid.link/20260902203722.926528-1-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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