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

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Message-ID: <Z8x5pI0suqOiZPId@mini-arch>
Date: Sat, 8 Mar 2025 09:08:52 -0800
From: Stanislav Fomichev <stfomichev@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Stanislav Fomichev <sdf@...ichev.me>, 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 03/08, Eric Dumazet wrote:
> 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

Ah, yes, I was waiting for a repro, but should have attached the proper
tags, thanks!