[lxc-users] zombie process blocks stopping of container

[Serge Hallyn]

Quoting Stéphane Graber (stgraber at ubuntu.com):
> On Tue, Jun 03, 2014 at 04:56:03PM +0200, Tamas Papp wrote:
> > 
> > On 06/03/2014 04:50 PM, Stéphane Graber wrote:
> > >lxc-stop will send SIGPWR (or the equivalent signal) to the container,
> > >wait 30s then SIGKILL init. lxc-stop -k will skip the SIGPWR step,
> > >lxc-stop --nokill will skip the SIGKILL step.
> > >
> > >It's pretty odd that init after a kill -9 is still marked running... I'd
> > >have expected it to either go away or get stuck in D state if
> > >something's really wrong...
> > >
> > >Do you see anything relevant in the kernel log?
> > 
> > Nothing. I was in hurry, so I restarted the whole machine, I cannot
> > collect more information.
> > Unfortunately I'm pretty sure it will be back soon, since this was
> > not the first time.
> > What do you suggest, what should I check, when I face it again?
> 
> So my hope would be for the kernel to report the task as hung which
> causes a stacktrace to be dumped in dmesg. If not, then it's going to be
> a bit harder to figure it out...

Both the container init and its lxc monitor where in S state.  I assume
a sigcont sent to one or both of those would have fixed it.   Until that
happens, any other tasks in the container will indeed be zombies waiting
for the container init to reap them.

The question is why container init and monitor were stopped.