Closing unused descriptors

[Jean-Christian de Rivaz]

Hi Aleksander,

Le 24. 09. 15 13:10, Aleksander Morgado a écrit :
> On Thu, Sep 24, 2015 at 9:49 AM, Jean-Christian de Rivaz <jc at eclis.ch> wrote:
>> While trying to reproduce a bug by power cycling a USB modem 4 time per
>> hour, I faced this message from the kernel:
>>
>> cdc_acm 1-2:1.0: no more free acm devices
>>
>> I found the the problem is caused by ModemManager that still have file
>> descriptors open on old ports that was deleted, preventing the kernel to
>> recycle the port numbers:
>>
>> ls -al /proc/$(pgrep ModemManager)/fd
>> total 0
>> dr-x------ 2 root root  0 Sep 24 01:44 .
>> dr-xr-xr-x 7 root root  0 Sep 24 01:44 ..
>> lr-x------ 1 root root 64 Sep 24 01:44 0 -> /dev/null
>> lrwx------ 1 root root 64 Sep 24 01:44 1 -> socket:[218296]
>> lrwx------ 1 root root 64 Sep 24 01:44 10 -> /dev/ttyACM4 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 11 -> /dev/ttyACM5 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 12 -> /dev/ttyACM6 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 13 -> /dev/ttyACM7 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 14 -> /dev/ttyACM8 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 15 -> /dev/ttyACM11 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 16 -> /dev/ttyACM10 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 17 -> /dev/ttyACM12 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 18 -> /dev/ttyACM13 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 19 -> /dev/ttyACM14 (deleted)
>> l-wx------ 1 root root 64 Sep 24 01:44 2 -> /dev/null
>> lrwx------ 1 root root 64 Sep 24 01:44 20 -> /dev/ttyACM15 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 21 -> /dev/ttyACM16 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 22 -> /dev/ttyACM17 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 23 -> /dev/ttyACM18 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 24 -> /dev/ttyACM19 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 25 -> /dev/ttyACM20 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 26 -> /dev/ttyACM21 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 27 -> /dev/ttyACM23 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 28 -> /dev/ttyACM9 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 29 -> /dev/ttyACM24 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 3 -> anon_inode:[eventfd]
>> lrwx------ 1 root root 64 Sep 24 01:44 30 -> /dev/ttyACM25 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 31 -> /dev/ttyACM26 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 32 -> /dev/ttyACM27 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 33 -> /dev/ttyACM28 (deleted)
>> lrwx------ 1 root root 64 Sep 24 04:35 34 -> /dev/ttyACM22 (deleted)
>> lrwx------ 1 root root 64 Sep 24 04:36 37 -> /dev/ttyACM30 (deleted)
>> lrwx------ 1 root root 64 Sep 24 04:49 38 -> /dev/ttyACM31 (deleted)
>> lrwx------ 1 root root 64 Sep 24 04:36 39 -> /dev/ttyACM29 (deleted)
>> lrwx------ 1 root root 64 Sep 24 01:44 4 -> anon_inode:[eventfd]
>> lrwx------ 1 root root 64 Sep 24 01:44 5 -> socket:[218298]
>> lrwx------ 1 root root 64 Sep 24 01:44 6 -> socket:[218304]
>> lrwx------ 1 root root 64 Sep 24 01:44 7 -> anon_inode:[eventfd]
>> lrwx------ 1 root root 64 Sep 24 01:44 8 -> socket:[218306]
>> lrwx------ 1 root root 64 Sep 24 01:44 9 -> /dev/ttyACM3 (deleted)
>>
>> To me it look like a ModemManager bug: it must close descriptors that it no
>> longer use at all.
>>
>> This was tester with MM 1.4.0 from Debian Jessie with the generic driver.
> Any chance you can retest with latest git master or latest 1.4.x?

I will try to compile it. This will take a long time on a ~0.5GHz 
Cortex-A5 ...

> When you power cycle the modem 4 times per hour, do you just cut the
> power to the modem externally?
>

Yes, for 10 minutes before power it up again. The lsusb and dmesg 
clearly show that all the CDC of the modem disconnected at the power 
off. Probably the udev noticed the event too, I have not verified.

Regards,
Jean-Christian