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

[Brian Inglis <Brian dot Inglis at SystematicSw dot ab dot ca>]

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@nexgo.de> 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?

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)'
Error initializing source driver; source='s_local', id='s_local#0'
Error initializing message pipeline;
... [repeats]

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

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