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

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Message-ID: <20241001204849.11878-1-kuniyu@amazon.com>
Date: Tue, 1 Oct 2024 13:48:49 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <edumazet@...gle.com>
CC: <davem@...emloft.net>, <kuba@...nel.org>, <kuni1840@...il.com>,
	<kuniyu@...zon.com>, <netdev@...r.kernel.org>, <pabeni@...hat.com>
Subject: Re: [PATCH v1 net-next 1/3] rtnetlink: Add per-net RTNL.

From: Eric Dumazet <edumazet@...gle.com>
Date: Tue, 1 Oct 2024 14:18:39 +0200
> 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.

Agreed, and there's no user for now.
I'll include the revert in v2.

Thanks!