netdev - Re: [PATCH net] net: core: Fix the loop in default_device_exit

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Message-ID: <CAAVpQUC_sH2UDdf0e5c=iPFU5EcaB7YeN=__2j6w_h6_pe8m_g@mail.gmail.com>
Date: Sat, 19 Jul 2025 13:47:37 -0700
From: Kuniyuki Iwashima <kuniyu@...gle.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Haiyang Zhang <haiyangz@...ux.microsoft.com>, linux-hyperv@...r.kernel.org, 
	netdev@...r.kernel.org, haiyangz@...rosoft.com, kys@...rosoft.com, 
	wei.liu@...nel.org, edumazet@...gle.com, pabeni@...hat.com, horms@...nel.org, 
	davem@...emloft.net, sdf@...ichev.me, ahmed.zaki@...el.com, 
	aleksander.lobakin@...el.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: core: Fix the loop in default_device_exit_net()

On Fri, Jul 18, 2025 at 4:37 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Fri, 18 Jul 2025 13:20:14 -0700 Haiyang Zhang wrote:
> > The loop in default_device_exit_net() won't be able to properly detect the
> > head then stop, and will hit NULL pointer, when a driver, like hv_netvsc,
> > automatically moves the slave device together with the master device.
> >
> > To fix this, add a helper function to return the first migratable netdev
> > correctly, no matter one or two devices were removed from this net's list
> > in the last iteration.
>
> FTR I think that what the driver is trying to do is way too hacky, and
> it should be fixed instead. But I defer to Kuniyuki for the final word,
> maybe this change is useful for other reasons..

I agree that it should be fixed on the driver side.  I don't
think of a good reason for the change.