netdev - Re: [AX25] patch did not fix -- was: ax25: fix incorrect dev

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Date:   Mon, 24 Oct 2022 13:56:40 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Thomas Osterried <thomas@...erried.de>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        Bernard Pidoux <f6bvp@...e.fr>,
        Duoming Zhou <duoming@....edu.cn>, netdev@...r.kernel.org,
        linux-hams@...r.kernel.org
Subject: Re: [AX25] patch did not fix --  was: ax25: fix incorrect
 dev_tracker usage

On Mon, 24 Oct 2022 20:00:00 +0200 Thomas Osterried wrote:
>  II) What consequences has the tracker counter?
> 
>      As far as I can see by kernel messages, the netdev tracker forces the
>      kernel to wait
>        (on ifdown (i.e. ifconfig ax0 down) 
>         or rmmod (i.e. rmmod bpqether or rmmod ax25) )
>      until all references to the network device are freed.
>      If there's a bug (refcount > 0 or < 0), kernel obviously waits for ever.

Small correction here - the wait is when netdev is unregistered,
which often happens on rmmod, but also when user asks for a sw
netdev to be deleted, or HW device is removed, etc.

> III) Is it only to track sessions initiated from userspace?
> 
>      I think no.

Correct, the trackers track the references taken on the device.
Doesn't really matter if the reference is somehow tracable to
a user request or not.

Sorry for lack of input on the actual ax25 problem, I had looked
briefly in September and it wasn't obvious how things work :S