Comment 58 for bug 1011792

I think that pretty surely is the reason that Arch is different. That flag will cause Xen to use its own paravirtualized spinlocks which I am suspecting of causing the problems (in some way related to having tasks in taskgroups which autogroup does automatically to happen). This seems, when the conditions are right, to cause a deadlock situation.

For now (as figuring out the problem and getting a solution could prove to take a bit) I think the best work-around for affected production systems is "noautogroup". That could then be removed as soon as we got a proper solution.