Re: [PATCH v6 net-next 00/15] neighbour: Namespacify arp_tbl and nd_tbl.

[Ido Schimmel <idosch@nvidia.com>]

On Wed, Sep 02, 2026 at 08:36:41PM +0000, 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.
> 
> After this series, I will follow up on two suggestions by Ido:
> https://lore.kernel.org/netdev/20260902143023.GA3966681@shredder/

Reviewed-by: Ido Schimmel <idosch@nvidia.com>

Thanks!