I'm leaning towards something in the test. I'll check if reverting these changes alters the results. I don't imagine it will.
The real question is which thread it fails on and at what point in time. My patches only changed the order of operations where threads enter the cpuset cgroups at a slightly different time. And the qemu main thread never enters the parent group, it becomes an emulator-thread. Maybe you can point to exactly the assertion that fails. Including a link to the test code. And yes if you can confirm that the patches are to blame that would be a good first step ;).
Thanks, Henning
Update: I have found that if I revert patch 2... Then modify qemuInitCgroup() to modify the virCgroupNewMachine check to also ensure "|| !priv->cgroup) Then modify qemuSetupCgroupForEmulator() to make the virCgroupAddTask() call like was in patch 2 Then modify patch 3 (qemuSetupCgroupForVcpu) to change the call: if (!cpumap) continue; if (qemuSetupCgroupCpusetCpus(cgroup_vcpu, cpumap) < 0) goto cleanup; to if (cpumap && qemuSetupCgroupCpusetCpus(cgroup_vcpu, cpumap) < 0) goto cleanup; Then retest and the test passes again. Note that taking this route, I found that when I start the guest, I have the following in 'tasks': # cat /sys/fs/cgroup/memory/machine.slice/tasks # cat /sys/fs/cgroup/memory/machine.slice/*/tasks 15007 15008 15010 15011 15013 # Where '15007' is the virt-tests-vm1 process (eg, /proc/$pid/cgroup). If I read the intentions you had, this follows that... I'll post a couple of patches in a bit... John