Infinite connection loop

[Aleksander Morgado]

Hey,

> I am running an embedded system with a u-blox SARA-U270 modem and NetworkManager 1.12.2 / ModemManager 1.8.0. For some reason, the modem connection seems to break over time. I am not quite sure why that’s the case, but when I look into the journal, I see NetworkManager and ModemManager spewing out log messages at a very high rate. This actually causes significant system load (mostly by dbus-daemon). Here’s an excerpt of the messages:
>
> Oct 17 12:54:29 cf352c1 ModemManager[1385]: Simple connect started...
> Oct 17 12:54:29 cf352c1 ModemManager[1385]: Simple connect state (4/8): Wait to get fully enabled
> Oct 17 12:54:29 cf352c1 ModemManager[1385]: Simple connect state (5/8): Register
> Oct 17 12:54:29 cf352c1 ModemManager[1385]: Simple connect state (6/8): Bearer
> Oct 17 12:54:29 cf352c1 ModemManager[1385]: Simple connect started...
> Oct 17 12:54:29 cf352c1 ModemManager[1385]: Simple connect state (4/8): Wait to get fully enabled
> Oct 17 12:54:29 cf352c1 ModemManager[1385]: Simple connect state (5/8): Register
> Oct 17 12:54:29 cf352c1 ModemManager[1385]: Simple connect state (6/8): Bearer
> Oct 17 12:54:29 cf352c1 NetworkManager[677]: <warn>  [1539780869.7776] modem-broadband[ttyACM0]: failed to connect modem: Could not open serial device ttyACM0: it has been forced close
> Oct 17 12:54:29 cf352c1 NetworkManager[677]: <info>  [1539780869.7778] device (ttyACM0): state change: prepare -> failed (reason 'unknown', sys-iface-state: 'managed')
> Oct 17 12:54:29 cf352c1 NetworkManager[677]: <info>  [1539780869.7807] manager: NetworkManager state is now CONNECTED_LOCAL
> Oct 17 12:54:29 cf352c1 NetworkManager[677]: <warn>  [1539780869.7840] device (ttyACM0): Activation: failed for connection 'gprsconnection'
> Oct 17 12:54:29 cf352c1 NetworkManager[677]: <info>  [1539780869.7860] device (ttyACM0): state change: failed -> disconnected (reason 'none', sys-iface-state: 'managed')
> Oct 17 12:54:29 cf352c1 NetworkManager[677]: <info>  [1539780869.7923] policy: auto-activating connection 'gprsconnection' (14e02637-0ffb-3a28-806f-ad60904afe7f)
> Oct 17 12:54:29 cf352c1 NetworkManager[677]: <info>  [1539780869.8005] device (ttyACM0): Activation: starting connection 'gprsconnection' (14e02637-0ffb-3a28-806f-ad60904afe7f)
> Oct 17 12:54:29 cf352c1 NetworkManager[677]: <info>  [1539780869.8015] device (ttyACM0): state change: disconnected -> prepare (reason 'none', sys-iface-state: 'managed')
> Oct 17 12:54:29 cf352c1 NetworkManager[677]: <info>  [1539780869.8043] manager: NetworkManager state is now CONNECTING
> Oct 17 12:54:29 cf352c1 ModemManager[1385]: Simple connect started...
> Oct 17 12:54:29 cf352c1 ModemManager[1385]: Simple connect state (4/8): Wait to get fully enabled
> Oct 17 12:54:29 cf352c1 ModemManager[1385]: Simple connect state (5/8): Register
> Oct 17 12:54:29 cf352c1 ModemManager[1385]: Simple connect state (6/8): Bearer
> Oct 17 12:54:29 cf352c1 ModemManager[1385]: Simple connect started...
> Oct 17 12:54:29 cf352c1 ModemManager[1385]: Simple connect state (4/8): Wait to get fully enabled
> Oct 17 12:54:29 cf352c1 ModemManager[1385]: Simple connect state (5/8): Register
> Oct 17 12:54:29 cf352c1 ModemManager[1385]: Simple connect state (6/8): Bearer
> Oct 17 12:54:29 cf352c1 NetworkManager[677]: <warn>  [1539780869.9321] modem-broadband[ttyACM0]: failed to connect modem: Could not open serial device ttyACM0: it has been forced close
> Oct 17 12:54:29 cf352c1 NetworkManager[677]: <info>  [1539780869.9323] device (ttyACM0): state change: prepare -> failed (reason 'unknown', sys-iface-state: 'managed')
> Oct 17 12:54:29 cf352c1 NetworkManager[677]: <info>  [1539780869.9350] manager: NetworkManager state is now CONNECTED_LOCAL
> Oct 17 12:54:29 cf352c1 NetworkManager[677]: <warn>  [1539780869.9399] device (ttyACM0): Activation: failed for connection 'gprsconnection'
> Oct 17 12:54:29 cf352c1 NetworkManager[677]: <info>  [1539780869.9430] device (ttyACM0): state change: failed -> disconnected (reason 'none', sys-iface-state: 'managed')
> Oct 17 12:54:29 cf352c1 NetworkManager[677]: <info>  [1539780869.9490] policy: auto-activating connection 'gprsconnection' (14e02637-0ffb-3a28-806f-ad60904afe7f)
> Oct 17 12:54:29 cf352c1 NetworkManager[677]: <info>  [1539780869.9569] device (ttyACM0): Activation: starting connection 'gprsconnection' (14e02637-0ffb-3a28-806f-ad60904afe7f)
> Oct 17 12:54:29 cf352c1 NetworkManager[677]: <info>  [1539780869.9585] device (ttyACM0): state change: disconnected -> prepare (reason 'none', sys-iface-state: 'managed')
> Oct 17 12:54:29 cf352c1 NetworkManager[677]: <info>  [1539780869.9653] manager: NetworkManager state is now CONNECTING
>
> It continues like that forever. My modem network connection config is as follows:
>
> [connection]
> id=gprsconnection
> type=gsm
> autoconnect=true
> autoconnect-retries=0
> [gsm]
> number=*99#
> [ipv4]
> dns-search=
> method=auto
> may-fail=false
>
> I have been looking through the code and what I don’t understand is why the ttyACM0 would ever be forcefully closed. What could be an explanation for this?
>
> Any insight is appreciated.
>

Do you have a full log of when this issue happens? If you can
reproduce this more or less frequently, could you setup both
ModemManager and NetworkManager to dump debug logs and try to get it
reproduced? This issue could be to a wrong synchronization between MM
and NM/pppd, in particular related to the CLOCAL settings in each case
(i.e. MM shouldn't get HUPs in the serial port unless for the cases
where the port is going away).

-- 
Aleksander
https://aleksander.es