netdev - Re: [RFC PATCH net-next 1/4] net-sysfs: remove rtnl

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Message-ID: <CANn89iJ0BMu3jDOmQCkiiOe_1Fc7bZuj-p7CZcL5RC53=-MDFQ@mail.gmail.com>
Date: Fri, 3 Jan 2025 09:41:20 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Antoine Tenart <atenart@...nel.org>, davem@...emloft.net, pabeni@...hat.com, 
	netdev@...r.kernel.org, gregkh@...uxfoundation.org, mhocko@...e.com, 
	stephen@...workplumber.org
Subject: Re: [RFC PATCH net-next 1/4] net-sysfs: remove rtnl_trylock from
 device attributes

On Thu, Jan 2, 2025 at 11:36 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Wed, 18 Oct 2023 17:47:43 +0200 Antoine Tenart wrote:
> > We have an ABBA deadlock between net device unregistration and sysfs
> > files being accessed[1][2]. To prevent this from happening all paths
> > taking the rtnl lock after the sysfs one (actually kn->active refcount)
> > use rtnl_trylock and return early (using restart_syscall)[3] which can
> > make syscalls to spin for a long time when there is contention on the
> > rtnl lock[4].
>
> Hi Antoine!
>
> I was looking at the sysfs locking, and ended up going down a very
> similar path. Luckily lore search for sysfs_break_active_protection()
> surfaced this thread so I can save myself some duplicated work :)
>
> Is there any particular reason why you haven't pursued this solution
> further? I think it should work.
>
> My version, FWIW:
> https://github.com/kuba-moo/linux/commit/2724bb7275496a254b001fe06fe20ccc5addc9d2

Indeed, this would probably remove a lot of syzbot reports.