Comment 69 for bug 1518457

I've bisected systemd and found the commit that triggers the bug. http://bazaar.launchpad.net/~thopiekar/systemd/systemd-packaging-ubuntu-wily/revision/1706 seems to be the one. The commit is a bugfix that effectively enables hotadd for Xen. That can explain why more or less only Ubuntu 15.10 is affected, but the underlying mechanism is in the kernel.

A working workaround on the latest 15.10 is to comment out line 2 (ATTR{[dmi/id]sys_vendor}=="Xen", GOTO="vm_hotadd_apply") in /lib/udev/rules.d/40-vm-hotadd.rules