netdev - Re: [PATCH v1 net-next 1/8] rtnetlink: Introduce struct rtnl

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Message-ID: <CANn89iJX+Z81vsx5=mbWN_gGDuzQ2e8W51NQic1Gg-kgjcO_tQ@mail.gmail.com>
Date: Tue, 5 Nov 2024 11:16:27 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Andrew Lunn <andrew+netdev@...n.ch>, Marc Kleine-Budde <mkl@...gutronix.de>, 
	Vincent Mailhol <mailhol.vincent@...adoo.fr>, Daniel Borkmann <daniel@...earbox.net>, 
	Nikolay Aleksandrov <razor@...ckwall.org>, Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v1 net-next 1/8] rtnetlink: Introduce struct rtnl_nets and helpers.

On Tue, Nov 5, 2024 at 3:05 AM Kuniyuki Iwashima <kuniyu@...zon.com> 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@...zon.com>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>