netdev - Re: [PATCH v1 net-next 1/3] rtnetlink: Add per-net RTNL.

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Message-ID: <CANn89i+KoYzUH+VPLdGmLABYf5y4TW0hrM4UAeQQJ9AREty0iw@mail.gmail.com>
Date: Tue, 1 Oct 2024 14:18:39 +0200
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>, Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v1 net-next 1/3] rtnetlink: Add per-net RTNL.

On Mon, Sep 30, 2024 at 10:27 PM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>
> The goal is to break RTNL down into per-net mutex.
>
> This patch adds per-net mutex and its helper functions, rtnl_net_lock()
> and rtnl_net_unlock().
>
> rtnl_net_lock() acquires the global RTNL and per-net RTNL mutex, and
> rtnl_net_unlock() releases them.
>
> We will replace 800+ rtnl_lock() instances with rtnl_net_lock() and
> finally removes rtnl_lock() in rtnl_net_lock().
>
> When we need to nest per-net RTNL mutex, we will use __rtnl_net_lock(),
> and its locking order is defined by rtnl_net_lock_cmp_fn() as follows:
>
>   1. init_net is first
>   2. netns address ascending order
>
> Note that the conversion will be done under CONFIG_DEBUG_NET_SMALL_RTNL
> with LOCKDEP so that we can carefully add the extra mutex without slowing
> down RTNL operations during conversion.
>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> ---
>  include/linux/rtnetlink.h   | 13 +++++++++
>  include/net/net_namespace.h |  4 +++
>  net/Kconfig.debug           | 14 +++++++++
>  net/core/net_namespace.c    |  6 ++++
>  net/core/rtnetlink.c        | 58 +++++++++++++++++++++++++++++++++++++
>  5 files changed, 95 insertions(+)
>
> diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
> index a7da7dfc06a2..c4afe6c49651 100644
> --- a/include/linux/rtnetlink.h
> +++ b/include/linux/rtnetlink.h
> @@ -49,6 +49,19 @@ extern bool refcount_dec_and_rtnl_lock(refcount_t *r);
>
>  DEFINE_LOCK_GUARD_0(rtnl, rtnl_lock(), rtnl_unlock())

We probably should revert 464eb03c4a7c ("rtnetlink: add guard for
RTNL") because I doubt
this will ever be used once we have a per-netns rtnl.