netdev - Re: [PATCH net-next v1] dev: remove netdev_lock() and netdev_lock_ops() in register

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Message-ID: <20250308144142.4f68c0be@kernel.org>
Date: Sat, 8 Mar 2025 14:41:42 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Kohei Enju <enjuk@...zon.com>
Cc: <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <bpf@...r.kernel.org>, "David S . Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Simon
 Horman <horms@...nel.org>, Kuniyuki Iwashima <kuniyu@...zon.com>, Sebastian
 Andrzej Siewior <bigeasy@...utronix.de>, "Ahmed Zaki"
 <ahmed.zaki@...el.com>, Stanislav Fomichev <sdf@...ichev.me>, "Alexander
 Lobakin" <aleksander.lobakin@...el.com>, Kohei Enju <kohei.enju@...il.com>
Subject: Re: [PATCH net-next v1] dev: remove netdev_lock() and
 netdev_lock_ops() in register_netdevice().

On Sat, 8 Mar 2025 13:18:13 -0800 Jakub Kicinski wrote:
> On Sun, 9 Mar 2025 05:37:18 +0900 Kohei Enju wrote:
> > Both netdev_lock() and netdev_lock_ops() are called before
> > list_netdevice() in register_netdevice().
> > No other context can access the struct net_device, so we don't need these
> > locks in this context.  
> 
> Doesn't sysfs get registered earlier?
> I'm afraid not being able to take the lock from the registration
> path ties our hands too much. Maybe we need to make a more serious
> attempt at letting the caller take the lock?

Looking closer at the report - we are violating the contract that only
drivers which opted in get their ops called under the instance lock.
iavf had a similar problem but it had to opt in. WiFi doesn't.

Maybe we can bring the address semaphore back?
We just need to take it before the ops lock in do_setlink.
A bit ugly but would work?