Re: [PATCH v4 net-next 00/15] neighbour: Namespacify arp_tbl and nd_tbl.

[Nikolay Aleksandrov <razor@blackwall.org>]

On 13/08/2026 11:02, Kuniyuki Iwashima wrote:
> 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.
> 
> 
> Changes:
>    v4:
>      * Patch 12
>        * Add sysctl knob, net.core.neigh_inherit_init_net
>        * Inherit all neigh parms by default
> 
>    v3: https://lore.kernel.org/netdev/20260811022448.116235-1-kuniyu@google.com/
>      * Add Patch 1 & 11
>      * Patch 12
>        * Remove timer_shutdown_sync() in neigh_flush_one() and
>          rely on tbl->entries (Patch 11) to free it in neigh_table_free().
>      * Patch 15
>        * Remove stale comments
> 
>    v2: https://lore.kernel.org/netdev/20260807232932.3986667-1-kuniyu@google.com/
>      * Add Patch 11 & 13
>      * Patch 7
>        * Add note about mlx5e_tc_update_neigh_used_value()
>      * Patch 9
>        * Add __maybe_unused to net in neigh_table_clear()
>      * Patch 10
>        * panic() when register_pernet_subsys(&arp_net_ops) fails
>        * Add timer_shutdown_sync() in neigh_flush_one()
>      * Patch 11
>        * Split from the next patch
>        * Remove net comparison in pneigh_dump_table()
>        * Remove net arg of pneigh_create(), pneigh_delete(), and
>          pneigh_lookup()
> 
>    v1: https://lore.kernel.org/netdev/20260806011152.1170012-1-kuniyu@google.com/
> 
> 
> Kuniyuki Iwashima (15):
>    selftest: net: Deflake Periodic GC test in test_neigh.sh.
>    neighbour: Remove __neigh_for_each_release().
>    neighbour: Remove lock dance for neigh_update_{gc,managed}_list().
>    neighbour: Remove unnecessary EXPORT_SYMBOL().
>    neighbour: Remove __rcu from neigh_tables[].
>    neighbour: Store arp_tbl and nd_tbl in net->neigh_tables[].
>    neighbour: Remove neigh_tables[].
>    ipv4: Replace &arp_tbl with arp_table(net).
>    ipv6: Replace &nd_tbl with nd_table(net).
>    neighbour: Clean up neigh_table_init() and neigh_table_clear().
>    neighbour: Convert neigh_table.entries to refcount_t.
>    neighbour: Namespacify neigh_tables.
>    neighbour: Don't store net in struct pneigh_entry.
>    neighbour: Remove unnecessary net_eq().
>    selftest: net: Specify netns for ip ntable in test_neigh.sh.
> 
>   Documentation/admin-guide/sysctl/net.rst      |  14 +
>   drivers/infiniband/ulp/ipoib/ipoib_main.c     |  27 +-
>   .../marvell/prestera/prestera_router.c        |  10 +-
>   .../mellanox/mlx5/core/en/rep/neigh.c         |  29 +-
>   .../mellanox/mlx5/core/en/tc_tun_encap.c      |  23 +-
>   .../mellanox/mlx5/core/en_accel/ipsec.c       |   6 +-
>   .../ethernet/mellanox/mlxsw/spectrum_router.c |  31 +-
>   .../ethernet/mellanox/mlxsw/spectrum_span.c   |  10 +-
>   .../netronome/nfp/flower/tunnel_conf.c        |  14 +-
>   drivers/net/ethernet/rocker/rocker_main.c     |   2 +-
>   drivers/net/ethernet/rocker/rocker_ofdpa.c    |   2 +-
>   drivers/net/ethernet/sfc/tc_counters.c        |   8 +-
>   drivers/net/ethernet/sfc/tc_encap_actions.c   |   4 +-
>   drivers/net/vrf.c                             |   2 +-
>   drivers/net/vxlan/vxlan_core.c                |  16 +-
>   include/net/arp.h                             |  10 +-
>   include/net/ndisc.h                           |  20 +-
>   include/net/neighbour.h                       |  22 +-
>   include/net/net_namespace.h                   |   4 +
>   include/net/route.h                           |   7 +-
>   net/bridge/br_arp_nd_proxy.c                  |   4 +-
>   net/core/neighbour.c                          | 400 +++++++++---------
>   net/core/sysctl_net_core.c                    |  12 +
>   net/ieee802154/6lowpan/tx.c                   |   3 +-
>   net/ipv4/arp.c                                | 131 ++++--
>   net/ipv4/devinet.c                            |  18 +-
>   net/ipv4/fib_semantics.c                      |   7 +-
>   net/ipv4/route.c                              |   2 +-
>   net/ipv6/addrconf.c                           |  17 +-
>   net/ipv6/ip6_output.c                         |   4 +-
>   net/ipv6/ndisc.c                              | 146 ++++---
>   net/ipv6/route.c                              |  18 +-
>   tools/testing/selftests/net/test_neigh.sh     |  66 +--
>   33 files changed, 620 insertions(+), 469 deletions(-)
> 

Nice work! With init_net inherit as default, for the set:
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>

Cheers,
  Nik