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Re: Odd hang in python waiting for child; strace wakes hung process?

On 2018-03-25 04:24, Corinna Vinschen wrote:
> On Mar 23 19:21, Brian Inglis wrote:
>> On 2018-03-22 10:59, Corinna Vinschen wrote:
>>> On Mar 21 23:41, Brian Inglis wrote:
>>>> On 2018-03-21 16:07, Dan Kegel wrote:
>>>>> On Wed, Mar 21, 2018 at 11:54 AM, Achim Gratz <Stromeko@xxxxxxxx> wrote:
>>>>>> Well, with the sporadic hanging/defunct processes at work my routine is
>>>>>> to send CONT to all Cygwin processes, then HUP/KILL to anything that's
>>>>>> still not live or gone and then another round of CONT.  This works
>>>>>> _most_ of the time, anything more stubborn I /bin/kill -f usually.
>>>>> Since I wrote, both bots hung again.  This time I verified:
>>>>> 0) both had the defunct git process as expected
>>>>> 1) kill -CONT the-pid doesn't do anything, nor does kill -9.  It's truly wedged.
>>>>> 2) the process stays in its spin hang until you ^C strace -p the-pid
>>>>> 3) ^C-ing the strace causes the process to terminate (strace alone doesn't)
>>>>> 4) taskkill /pid the-task /f also kills the process successfully.
>>>>> So I could write a script that watched for defunct git processes
>>>>> and taskkilled their parent.  Build jobs would fail, but at least
>>>>> the bot would stay up.  Of course it would be much nicer if
>>>>> the cygwin python process didn't get wedged.
>>>>> Alternately, I suppose I could try running native python...
>>>>> or cygwin's python3... but dangit, kill -9 should work.
>>>> Seems to be looping on access failure to a Windows mailslot; not sure what this
>>>> feature is normally used for: dmesg/syslog messages/AF_UNIX sockets?
>>> /dev/kmsg is implemented using a mailslot under the hood.  This
>>> feature is only used to log exceptions and for nothing else since
>>> nobody ever found another reason to use it for.
>>> It would be interesting to learn if the perl hangs have the same reason.
>>> I guess we can simply remove /dev/kmsg support completely and drop
>>> the mailslot code.  I'm pretty sure nobody would miss it.  Hardly
>>> anybody knows it exists...
>> Is /dev/log implemented the same way?
> No.  /dev/log is a AF_UNIX socket.
>> Looks like syslog-ng stopped working around the last upgrade:
>> $ cat /var/log/syslog-ng.log
>> Error reading serialized data; error='Error reading file (short read)'
>> Persistent configuration file is in invalid format, ignoring;
>> Error binding socket; addr='AF_UNIX(/dev/log)', error='Address already in use (112)'
> rm -rf /dev/log

$ ll /dev/log && /bin/rm -f /dev/log && ll /dev/log
-rw-rw-rw- 1 SYSTEM SYSTEM 54 Nov 24 20:59 /dev/log
ls: cannot access '/dev/log': No such file or directory
[start services]
$ cyg-srv-status.sh
cron Running   cygserver Running   sendmail Running   sshd Running   syslog-ng

Thank you very much!

Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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