Bug#663931: How to reproduce

[Jim Paris]

Hi,

This is not related to lvm2.  Libvirt is triggering a problem that
causes "udevadm settle" to stop working, and libvirt is also then
hitting that problem because it calls "udevadm settle" itself.

You can reproduce with just udev by running the following test program
(tested with kernel linux-image-3.2.0-2-amd64_3.2.14-1):

  /* test.c */
  #include <stdlib.h>
  #include <unistd.h>
  #include <sched.h>
  static int dummy(void *argv) { _exit(0); }
  main() {
          char stack[4096];
          clone(dummy, stack+4096, CLONE_NEWNET, NULL);
          wait();
          system("ip link set lo netns -1");
  }

e.g.:

  # /etc/init.d/udev restart
  Stopping the hotplug events dispatcher: udevd.
  Starting the hotplug events dispatcher: udevd.
  # time udevadm settle
    
  real    0m0.031s
  user    0m0.000s
  sys     0m0.004s
  # gcc -o test test.c
  # ./test
  # time udevadm settle

  real    2m0.160s
  user    0m0.008s
  sys     0m0.024s
  #

-jim