netdev - QMI QMAP interface stuck after power-cycling module

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Date:   Fri, 4 Dec 2020 08:53:09 +0100
From:   Kristian Evensen <kristian.evensen@...il.com>
To:     Network Development <netdev@...r.kernel.org>
Subject: QMI QMAP interface stuck after power-cycling module

Hi all,

I am using QMI together with QMAP when configuring and connecting my
LTE/5G modules. This all works well, but I have noticed something
strange when modules are disconnected from the host. Most disconnects
goes fine and everything related to module is removed, but sometimes
it happens that the network interface is stuck.

Even though the "disconnected" messages appear in dmesg, etc., I can
still see the network interfaces in the output from "ifconfig" or "ip
link". When I look in /sys/class/net, I can see that there either are
broken symlinks or regular files belonging to the interface that is
stuck. Running "ip link del" just gives an error, the same goes when I
try to clean up /sys/class/net manually.

There are no error messages printed in for example dmesg when the
problem occurs, and the modem works fine after it connects to my host
again (albeit with different network interface names). I have not been
able to reliably reproduce the issue, but I have so far only seen it
on "fast" (x86-based) devices. On the "slow" devices that I have
tested (like mt7621), I have not been able to trigger the problem. I
do not see the issue at all when using QMI without QMAP.

I tried to look at the code in qmi_wwan, but couldn't find anything
wrong. with the QMAP clean-up code. Does anyone know what might be
wrong or where to start or keep looking?

Thanks in advance for any help,
Kristian