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[Tycho Andersen <tycho.andersen@xxxxxxxxxxxxx>]

Public bug reported:

Consider the following,

root@dev:/tmp# mkdir foo
root@dev:/tmp# mount -t cgroup -o none,name=foo none foo
root@dev:/tmp# mkdir -p foo/bad
root@dev:/tmp# umount -l foo
root@dev:/tmp# mount -t cgroup -o none,name=foo none foo # hangs forever
^C
root@dev:/tmp# uname -a
Linux dev 4.4.0-22-generic #40-Ubuntu SMP Thu May 12 22:03:46 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

When I strace the mount task, I get a whole bunch of,

mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)

Which I think means that we're looping on,

https://github.com/torvalds/linux/blob/master/kernel/cgroup.c#L2137

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: Incomplete

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https://bugs.launchpad.net/bugs/1588056

Title:
  cgroupfs mounts can hang

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  Consider the following,

  root@dev:/tmp# mkdir foo
  root@dev:/tmp# mount -t cgroup -o none,name=foo none foo
  root@dev:/tmp# mkdir -p foo/bad
  root@dev:/tmp# umount -l foo
  root@dev:/tmp# mount -t cgroup -o none,name=foo none foo # hangs forever
  ^C
  root@dev:/tmp# uname -a
  Linux dev 4.4.0-22-generic #40-Ubuntu SMP Thu May 12 22:03:46 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

  When I strace the mount task, I get a whole bunch of,

  mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
  mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
  mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
  mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
  mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
  mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
  mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
  mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
  mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
  mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
  mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
  mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
  mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
  mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
  mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
  mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)
  mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ? ERESTARTNOINTR (To be restarted)

  Which I think means that we're looping on,

  https://github.com/torvalds/linux/blob/master/kernel/cgroup.c#L2137

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