linux-kernel - Re: [PATCH net-next] net: revert to lockless TC_SETUP_BLOCK and TC_SETUP

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Message-ID: <CANn89iLV6mLh8mWhYket7gBWTX+3TcCrJDA4EU5YU4ebV2nPYw@mail.gmail.com>
Date: Sat, 8 Mar 2025 07:41:28 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Stanislav Fomichev <sdf@...ichev.me>
Cc: netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org, 
	pabeni@...hat.com, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	netfilter-devel@...r.kernel.org, coreteam@...filter.org, horms@...nel.org, 
	corbet@....net, andrew+netdev@...n.ch, pablo@...filter.org, 
	kadlec@...filter.org
Subject: Re: [PATCH net-next] net: revert to lockless TC_SETUP_BLOCK and TC_SETUP_FT

On Sat, Mar 8, 2025 at 5:47 AM Stanislav Fomichev <sdf@...ichev.me> wrote:
>
> There is a couple of places from which we can arrive to ndo_setup_tc
> with TC_SETUP_BLOCK/TC_SETUP_FT:
> - netlink
> - netlink notifier
> - netdev notifier
>
> Locking netdev too deep in this call chain seems to be problematic
> (especially assuming some/all of the call_netdevice_notifiers
> NETDEV_UNREGISTER) might soon be running with the instance lock).
> Revert to lockless ndo_setup_tc for TC_SETUP_BLOCK/TC_SETUP_FT. NFT
> framework already takes care of most of the locking. Document
> the assumptions.
>


>
> Fixes: c4f0f30b424e ("net: hold netdev instance lock during nft ndo_setup_tc")
> Signed-off-by: Stanislav Fomichev <sdf@...ichev.me>

I think you forgot to mention syzbot.

Reported-by: syzbot+0afb4bcf91e5a1afdcad@...kaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/67cb88d1.050a0220.d8275.022d.GAE@google.com/T/#u

Thanks.