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

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Message-ID: <20250102143647.7963cbfd@kernel.org>
Date: Thu, 2 Jan 2025 14:36:47 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Antoine Tenart <atenart@...nel.org>
Cc: davem@...emloft.net, pabeni@...hat.com, edumazet@...gle.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 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