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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CLOUDSTACK-10305) Rare race condition in KVM migration
Date Mon, 26 Feb 2018 14:32:00 GMT

    [ https://issues.apache.org/jira/browse/CLOUDSTACK-10305?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16376953#comment-16376953
] 

ASF GitHub Bot commented on CLOUDSTACK-10305:
---------------------------------------------

rhtyd closed pull request #2466: CLOUDSTACK-10305: Rare race condition in KVM migration
URL: https://github.com/apache/cloudstack/pull/2466
 
 
   

This is a PR merged from a forked repository.
As GitHub hides the original diff on merge, it is displayed below for
the sake of provenance:

As this is a foreign pull request (from a fork), the diff is supplied
below (as it won't show otherwise due to GitHub magic):

diff --git a/plugins/hypervisors/kvm/src/com/cloud/hypervisor/kvm/resource/wrapper/LibvirtMigrateCommandWrapper.java
b/plugins/hypervisors/kvm/src/com/cloud/hypervisor/kvm/resource/wrapper/LibvirtMigrateCommandWrapper.java
index 30f0e20ddd9..ad32759a517 100644
--- a/plugins/hypervisors/kvm/src/com/cloud/hypervisor/kvm/resource/wrapper/LibvirtMigrateCommandWrapper.java
+++ b/plugins/hypervisors/kvm/src/com/cloud/hypervisor/kvm/resource/wrapper/LibvirtMigrateCommandWrapper.java
@@ -172,13 +172,21 @@ Use VIR_DOMAIN_XML_SECURE (value = 1) prior to v1.0.0.
 
                 // pause vm if we meet the vm.migrate.pauseafter threshold and not already
paused
                 final int migratePauseAfter = libvirtComputingResource.getMigratePauseAfter();
-                if (migratePauseAfter > 0 && sleeptime > migratePauseAfter
&& dm.getInfo().state == DomainState.VIR_DOMAIN_RUNNING ) {
-                    s_logger.info("Pausing VM " + vmName + " due to property vm.migrate.pauseafter
setting to " + migratePauseAfter+ "ms to complete migration");
+                if (migratePauseAfter > 0 && sleeptime > migratePauseAfter)
{
+                    DomainState state = null;
                     try {
-                        dm.suspend();
+                        state = dm.getInfo().state;
                     } catch (final LibvirtException e) {
-                        // pause could be racy if it attempts to pause right when vm is finished,
simply warn
-                        s_logger.info("Failed to pause vm " + vmName + " : " + e.getMessage());
+                        s_logger.info("Couldn't get VM domain state after " + sleeptime +
"ms: " + e.getMessage());
+                    }
+                    if (state != null && state == DomainState.VIR_DOMAIN_RUNNING)
{
+                        try {
+                            s_logger.info("Pausing VM " + vmName + " due to property vm.migrate.pauseafter
setting to " + migratePauseAfter + "ms to complete migration");
+                            dm.suspend();
+                        } catch (final LibvirtException e) {
+                            // pause could be racy if it attempts to pause right when vm
is finished, simply warn
+                            s_logger.info("Failed to pause vm " + vmName + " : " + e.getMessage());
+                        }
                     }
                 }
             }


 

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> Rare race condition in KVM migration
> ------------------------------------
>
>                 Key: CLOUDSTACK-10305
>                 URL: https://issues.apache.org/jira/browse/CLOUDSTACK-10305
>             Project: CloudStack
>          Issue Type: Bug
>      Security Level: Public(Anyone can view this level - this is the default.) 
>            Reporter: Nicolas Vazquez
>            Priority: Major
>             Fix For: 4.11.1.0
>
>
> There is a race condition in the monitoring of the migration process on KVM. If the monitor
wakes up in the tight window after the migration succeeds, but before the migration thread
terminates, the monitor will get a LibvirtException “Domain not found: no domain with matching
uuid” when checking on the migration status. This in turn causes CloudStack to sync the
VM state to stop, in which it issues a defensive StopCommand to ensure it is correctly synced.
> This is issue is reported under these conditions:
>  * VM migration has physically finished
>  * Migration thread executor is still not marked as terminated
> From the migration monitoring process, as VM has been migrated, that domain cannot be
found (we should get the destination domain from the migration thread later) and the LibvirtException
is thrown: {{LibvirtException “Domain not found: no domain with matching uuid”}}.
> So basically the idea is just logging the issue but not suspending the VM as the migration
has already been performed, but the migration thread is not marked as finished. Once the migrarion
thread is marked as finished, the migration monitoring process (while loop) ends and the migration
command wrapper would continue its execution.
> Regarding your last question, we won't need to suspend the VM in this case as the migration
has already been performed. VM suspension will take place whenever the migration is in progress
and those conditions are met



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