Bug 1364925

Summary:	VMs flip to non-responsive state for ever.
Product:	Red Hat Enterprise Virtualization Manager	Reporter:	Michal Skrivanek <michal.skrivanek>
Component:	vdsm	Assignee:	Francesco Romani <fromani>
Status:	CLOSED ERRATA	QA Contact:	sefi litmanovich <slitmano>
Severity:	high	Docs Contact:
Priority:	medium
Version:	3.6.7	CC:	acanan, bazulay, bgraveno, dougsland, fromani, gklein, ipinto, lsurette, mavital, mgoldboi, michal.skrivanek, mkalinin, obockows, rhodain, srevivo, ycui, ykaul, ylavi
Target Milestone:	ovirt-3.6.9	Keywords:	ZStream
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:	vdsm-4.17.34-1.el7ev.noarch	Doc Type:	If docs needed, set a value
Doc Text:	This update fixes an issue in the monitoring code which caused the VDSM to fail to detect that a stuck QEMU process has become responsive.	Story Points:	---
Clone Of:	1364924	Environment:
Last Closed:	2016-09-21 18:07:37 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	Virt	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	1361028, 1364924
Bug Blocks:

Description Michal Skrivanek 2016-08-08 08:28:13 UTC

clone job doesn't work, so doing that manually

+++ This bug was initially created as a clone of Bug #1364924 +++

clone job doesn't work, so doing that manually

+++ This bug was initially created as a clone of Bug #1361028 +++

Description of problem:
   When VMs get non responding. It can happen that in some cases the executor tasks queue get full and exception TooManyTasks is raised. This causes the operation not being scheduled any more.

Version-Release number of selected component (if applicable):
     vdsm-4.17.31-0.el7ev.noarch

How reproducible:
     Under heavy load and isue with qemu responsivness 

Steps to Reproduce:
     Not completely clear

Actual results:
     All VMs are marked as non-responding

Expected results:
     The task is scheduled as soon as there is some space in the tasks queue is 

Additional info:

vdsm.Scheduler::ERROR::2016-07-16 16:15:28,745::schedule::213::Scheduler::(_execute) Unhandled exception in <bound method Operation._try_to_dispatch of <virt.periodic.Operation object at 0x45ea390>>
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/vdsm/schedule.py", line 211, in _execute
    self._callable()
  File "/usr/share/vdsm/virt/periodic.py", line 190, in _try_to_dispatch
    self._dispatch()
  File "/usr/share/vdsm/virt/periodic.py", line 197, in _dispatch
    self._executor.dispatch(self, self._timeout)
  File "/usr/lib/python2.7/site-packages/vdsm/executor.py", line 101, in dispatch
    self._tasks.put((callable, timeout))
  File "/usr/lib/python2.7/site-packages/vdsm/executor.py", line 256, in put
    raise TooManyTasks()
TooManyTasks



vdsm/virt/periodic.py:
...
class Operation(object):
...
     def _dispatch(self):
         """
         Send `func' to Executor to be run as soon as possible.
         """
         self._call = None
         self._executor.dispatch(self, self._timeout)
         self._step()

The exception comes from 

    self._executor.dispatch(self, self._timeout)

So self._step() is not executed and the operation is not scheduled

Comment 1 Francesco Romani 2016-08-29 08:42:15 UTC

To reproduce:

1. modify /etc/vdsm/vdsm.conf, add those lines

[sampling]
periodic_workers = 1
periodic_task_per_worker = 1

2. restart vdsm

Now vdsm will have a very high chance to throw the TooManyTasks error, which triggers the condition which caused this bug.

Now we can use vdsClient (or engine or anything else) to see if stats are still updated or not.

Comment 2 sefi litmanovich 2016-08-31 13:10:29 UTC

Verified with rhevm-3.6.9-0.1.el6.noarch.
HOST: vdsm-4.17.34-1.el7ev.noarch

Followed comment 1:
1. Modified /etc/vdsm/vdsm.conf and added the lines:

[sampling]
periodic_workers = 1
periodic_task_per_worker = 1

2. restarted vdsm.
3. Created a vm pool with 8 vms.
4. Started all 8 vms.

result:

in vdsm log the new warning message wrapping the TooManyTask exception is issues in vdsm.log:

vdsm.Scheduler::WARNING::2016-08-29 15:27:12,161::periodic::203::virt.periodic.Operation::(_dispatch) could not run <V
mDispatcher operation=<class 'virt.periodic.BlockjobMonitor'> at 0x3be9590>, executor queue full

In the engine some of the vms are set to 'not responding' state for a short amount of time and when the previous tasks are done the vms are started as well until eventually all are up as expected.

Comment 6 errata-xmlrpc 2016-09-21 18:07:37 UTC

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHBA-2016-1925.html