netdev - Re: [PATCH net] vrf: fix vrf driver unloading

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Message-ID: <df95ef08-4b8f-1b23-9a8e-ae9ad0538a9d@kernel.org>
Date:   Wed, 25 May 2022 15:12:55 -0600
From:   David Ahern <dsahern@...nel.org>
To:     Eyal Birger <eyal.birger@...il.com>, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net] vrf: fix vrf driver unloading

On 5/25/22 2:46 PM, Eyal Birger wrote:
> The commit referenced in the "Fixes" tag has removed the vrf driver
> cleanup function leading to a "Device or resource busy" error when
> trying to rmmod vrf.
> 
> Fix by re-introducing the cleanup function with the relevant changes.
> 
> Fixes: 9ab179d83b4e ("net: vrf: Fix dst reference counting")
> Signed-off-by: Eyal Birger <eyal.birger@...il.com>
> 
> ----
> 
> Note: the commit message in 9ab179d83b4e did not document it
> and it is not apparent to me why the ability to rmmod the driver is
> linked to that change, but maybe there's some hidden reason.

dst output handler references VRF functions. You can not remove the
module until all dst references have been dropped. Since there is no way
to know and the rmmod command can not just hang waiting for dst entries
to be dropped the module can not be unloaded. The same is true for IPv6
as module; it can not be removed and I believe for the same reason.