netdev - Re: [PATCH v2 net-next] checkpatch: Discourage a new use of rtnl

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Message-ID: <CANn89iKY8V7jj=JkZpC2YuKtiUMr9-mDoJ7g7+0G9ppdOXo8ZQ@mail.gmail.com>
Date: Fri, 14 Feb 2025 15:15:48 +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>, Andy Whitcroft <apw@...onical.com>, 
	Joe Perches <joe@...ches.com>, Dwaipayan Ray <dwaipayanray1@...il.com>, 
	Lukas Bulwahn <lukas.bulwahn@...il.com>, Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v2 net-next] checkpatch: Discourage a new use of
 rtnl_lock() variants.

On Fri, Feb 14, 2025 at 5:54 AM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>
> rtnl_lock() is a "Big Kernel Lock" in the networking slow path
> and still serialises most of RTM_(NEW|DEL|SET)* rtnetlink requests.
>
> Commit 76aed95319da ("rtnetlink: Add per-netns RTNL.") started a
> very large, in-progress, effort to make the RTNL lock scope per
> network namespace.
>
> However, there are still some patches that newly use rtnl_lock(),
> which is now discouraged, and we need to revisit it later.
>
> Let's warn about the case by checkpatch.
>
> The target functions are as follows:
>
>   * rtnl_lock()
>   * rtnl_trylock()
>   * rtnl_lock_interruptible()
>   * rtnl_lock_killable()
>
> and the warning will be like:
>
>   WARNING: A new use of rtnl_lock() variants is discouraged, try to use rtnl_net_lock(net) variants
>   #18: FILE: net/core/rtnetlink.c:79:
>   +     rtnl_lock();

I do wonder if this is not premature.

After all, we have nothing in Documentation/ yet about this.