netdev - Re: [PATCH net] xfrm: always flush state and policy upon NETDEV_DOWN/NETDEV

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Message-ID: <fcbbbf70-f28c-4da8-be10-1863d4a6c0d8@I-love.SAKURA.ne.jp>
Date: Sun, 1 Feb 2026 23:17:24 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Leon Romanovsky <leon@...nel.org>, Sabrina Dubroca <sd@...asysnail.net>
Cc: Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
        Ilan Tayari <ilant@...lanox.com>, Guy Shapiro <guysh@...lanox.com>,
        Yossi Kuperman <yossiku@...lanox.com>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH net] xfrm: always flush state and policy upon
 NETDEV_DOWN/NETDEV_UNREGISTER events

On 2026/02/01 22:12, Leon Romanovsky wrote:
> I don't think that it is correct thing to adapt core code to something
> specific to netdevsim which was introduced to emulate missing HW device.
> Like in real HW device, the expectation is to have NETIF_F_HW_ESP bit,
> we should have that bit in netdevsim too.

I posted https://lkml.kernel.org/r/cea4b855-fe94-4b4e-9c2d-3cef7aac1be3@I-love.SAKURA.ne.jp
as what I think we should do regardless of netdevsim module.

syzbot is reporting "struct net_device" cannot be released because xfrm_dev_down()
cannot release reference to "struct net_device" unless NETIF_F_HW_ESP bit is set.

But I wonder when "struct xfrm_state" (without reference to "struct net_device") can be
released if xfrm_dev_down() becomes no-op due to checking for NETIF_F_HW_ESP bit;
I suspect there remains a resource leak bug unless xfrm_dev_unregister() is added.

Currently 50%+ reports of "unregister_netdevice: waiting for DEV to become free"
problem is hitting this xfrm path. Since there are other paths remaining, I want to
exclude xfrm path as quick as possible.

My question is, apart from how to fix netdevsim module, can my xfrm_dev_unregister()
patch be accepted?