Re: [PATCH v2 net-next 1/7] rtnetlink: Introduce struct rtnl_nets and helpers.

[Nikolay Aleksandrov <razor@blackwall.org>]

On Tue, Nov 05, 2024 at 06:24:26PM -0800, Kuniyuki Iwashima wrote:
> rtnl_newlink() needs to hold 3 per-netns RTNL: 2 for a new device
> and 1 for its peer.
> 
> We will add rtnl_nets_lock() later, which performs the nested locking
> based on struct rtnl_nets, which has an array of struct net pointers.
> 
> rtnl_nets_add() adds a net pointer to the array and sorts it so that
> rtnl_nets_lock() can simply acquire per-netns RTNL from array[0] to [2].
> 
> Before calling rtnl_nets_add(), get_net() must be called for the net,
> and rtnl_nets_destroy() will call put_net() for each.
> 
> Let's apply the helpers to rtnl_newlink().
> 
> When CONFIG_DEBUG_NET_SMALL_RTNL is disabled, we do not call
> rtnl_net_lock() thus do not care about the array order, so
> rtnl_net_cmp_locks() returns -1 so that the loop in rtnl_nets_add()
> can be optimised to NOP.
> 
> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> Reviewed-by: Eric Dumazet <edumazet@google.com>
> ---
> v2:
>   * Move struct rtnl_nets to net/core/rtnetlink.c
>   * Unexport rtnl_nets_add()
> ---
>  net/core/rtnetlink.c | 70 ++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 67 insertions(+), 3 deletions(-)
> 

Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>