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

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

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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@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?

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


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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