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[Seth Forshee <seth.forshee+lp@xxxxxxxxxxxxx>]

** Also affects: linux (Ubuntu Xenial)
   Importance: Undecided
       Status: New

** Changed in: linux (Ubuntu)
       Status: Incomplete => Confirmed

** Changed in: linux (Ubuntu Xenial)
   Importance: Undecided => High

** Changed in: linux (Ubuntu Xenial)
       Status: New => In Progress

** Changed in: linux (Ubuntu Xenial)
     Assignee: (unassigned) => Seth Forshee (sforshee)

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

Title:
  cgroupfs mounts can hang

Status in linux package in Ubuntu:
  Confirmed
Status in linux source package in Xenial:
  In Progress

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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