[Libguestfs] [ovirt-devel] virt-v2v become zombie via python cpopen on error

[Yaniv Bronheim]

yep, we don't wait for the process inside cpopen code - we expect the
caller to take care of it. if you use execCmd with sync=False (as in
virt-v2v) - you have to take care for killing the process and wait for its
pid after its done - you can see that with the fix  we raise exception and
this exception is caught in _import func and call _abort which calls kill
and sign the pid to zombiereaper which waits for it to die.
If you use execCmd with sync=True (the default) you can see that we wait
until process exists and return.

On Wed, Mar 30, 2016 at 5:30 PM, Nir Soffer <nsoffer at redhat.com> wrote:

> On Wed, Mar 30, 2016 at 3:32 PM, Shahar Havivi <shaharh at redhat.com> wrote:
> > On 30.03.16 14:28, Nir Soffer wrote:
> >> On Wed, Mar 30, 2016 at 1:36 PM, Michal Skrivanek
> >> <michal.skrivanek at redhat.com> wrote:
> >> >
> >> >> On 30 Mar 2016, at 11:49, Richard W.M. Jones <rjones at redhat.com>
> wrote:
> >> >>
> >> >> On Wed, Mar 30, 2016 at 12:19:35PM +0300, Shahar Havivi wrote:
> >> >>> Hi,
> >> >>>
> >> >>> We encounter a problem in VDSM project that virt-v2v become zombie
> task while
> >> >>> importing vm from vmware.
> >> >>> When virt-v2v is in 'copy disk' mode and we someone deletes the vm
> at vmware
> >> >>> the process hang in read() method,
> >> >>> I am pretty sure that its not virt-v2v problem because when I run
> it from the
> >> >>> shell virt-v2v exit with an error, still maybe someone have an
> idea....
> >> >>>
> >> >>> I wrote a small python script that encounter the problem:
> >> >>>
> >> >>>
> ----------------------------------------------------------------------------
> >> >>> from cpopen import CPopen
> >> >>>
> >> >>> env = {'LIBGUESTFS_BACKEND': 'direct'}
> >> >>> cmd = ['/usr/bin/virt-v2v', '-ic',
> >> >>>       'vpx://....', '-o',
> >> >>>       'local', '-os', '/tmp', '-of', 'raw', '-oa', 'sparse',
> >> >>>       '--password-file', '/tmp/passwd', '--machine-readable', 'bbb']
> >> >>> p = CPopen(cmd, env=env)
> >> >>> while p.returncode is None:
> >>
> >> p.returncode just return the instance variable, there is no wait()
> involved.
> >>
> >> The right way:
> >>
> >>     while p.poll() is None:
> > the problem is proc.stdout.read(1) didn't raise and error when the stream
> > closed but return ''.
> > its a CPopen behaviour and works differently in subprocess.
>
> No, it works the same in both, this was just a bug in our code.
> Fixed in https://gerrit.ovirt.org/55477
>
> >
> >>         ...
> >>
> >> p.returncode calling wait is non-standard feature in vdsm AsyncProc
> >> wrapper. This is
> >> the object used by v2v vdsm module, so there accessing p.returncode
> does call
> >> p.poll().
> >>
> >> These non-standard apis will be removed from vdsm, please do not use
> them.
> >>
> >> >>>    c = p.stdout.read(1)
> >> >>>    print c
> >> >>>
> ----------------------------------------------------------------------------
> >> >>
> >> >> An actual zombie task?  That would indicate that the parent process
> >> >> (your Python program) wasn't doing a wait system call.
> >> >>
> >> >> I downloaded the cpopen-1.4 program, and it doesn't appear to call
> any
> >> >> of the wait*(2) system calls anywhere, so that could be the problem.
> >> >
> >> > I suppose the cpopen parameters are not alright…I’m sure vdsm
> developers can help with that.
> >> >
> >> >>
> >> >> Rich.
> >> >>
> >> >> --
> >> >> Richard Jones, Virtualization Group, Red Hat
> http://people.redhat.com/~rjones
> >> >> Read my programming and virtualization blog:
> http://rwmj.wordpress.com
> >> >> virt-p2v converts physical machines to virtual machines.  Boot with a
> >> >> live CD or over the network (PXE) and turn machines into KVM guests.
> >> >> http://libguestfs.org/virt-v2v
> >> >
> >> > _______________________________________________
> >> > Devel mailing list
> >> > Devel at ovirt.org
> >> > http://lists.ovirt.org/mailman/listinfo/devel
> _______________________________________________
> Devel mailing list
> Devel at ovirt.org
> http://lists.ovirt.org/mailman/listinfo/devel
>



-- 
*Yaniv Bronhaim.*
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