linux-kernel - Re: [PATCH net-next v3 1/4] udp_tunnel: remove rtnl

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Message-ID: <aEo_2hOn5kh6kBpk@mini-arch>
Date: Wed, 11 Jun 2025 19:47:54 -0700
From: Stanislav Fomichev <stfomichev@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
	pabeni@...hat.com, skalluru@...vell.com, manishc@...vell.com,
	andrew+netdev@...n.ch, michael.chan@...adcom.com,
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	linux-net-drivers@....com, linux-kselftest@...r.kernel.org,
	leon@...nel.org, Cosmin Ratiu <cratiu@...dia.com>
Subject: Re: [PATCH net-next v3 1/4] udp_tunnel: remove rtnl_lock dependency

On 06/11, Jakub Kicinski wrote:
> On Tue, 10 Jun 2025 10:15:19 -0700 Stanislav Fomichev wrote:
> > Drivers that are using ops lock and don't depend on RTNL lock
> > still need to manage it because udp_tunnel's RTNL dependency.
> > Introduce new udp_tunnel_nic_lock and use it instead of
> > rtnl_lock. Drop non-UDP_TUNNEL_NIC_INFO_MAY_SLEEP mode from
> > udp_tunnel infra (udp_tunnel_nic_device_sync_work needs to
> > grab udp_tunnel_nic_lock mutex and might sleep).
> 
> There are multiple entry points to this code, basically each member of
> struct udp_tunnel_nic_ops and the netdev notifiers. In this patch only
> reset and work are locked. I'm a bit confused as to what is the new
> lock protecting :S

I though that most of the callers are from do_setlink and there we have
rtnl and we grab rtnl+lock during the sync. But that doesn't
address the suspend/resume vs do_setlink race, that's true :-(

Did not look deep into the notifiers, assuming they are a way to push
the info down to the devices (under rtnl) plus trigger the sync work,
will take a closer look.