Merge branch 'for-3.19-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup
Pull cgroup fix from Tejun Heo:
"The lifetime rules of cgroup hierarchies always have been somewhat
counter-intuitive and cgroup core tried to enforce that hierarchies
w/o userland-visible usages must die in finite amount of time so that
the controllers can be reused for other hierarchies; unfortunately,
this can't be implemented reasonably for the memory controller - the
kmemcg part doesn't have any way to forcefully drain the existing
usages, leading to an interruptible hang if a following mount attempts
to use the controller in any way.
So, it seems like we're stuck with "hierarchies live on till they die
whenever that may be" at least for now. This pretty much confines
attaching controllers to hierarchies to before the hierarchies are
actively used by making dynamic configurations post active usages
unreliable. This has never been reliable and should be fine in
practice given how cgroups are used.
After the patch, hierarchies aren't killed if it isn't already
drained. A following mount attempt of the same mount options will
reuse the existing hierarchy. Mount attempts with differing options
will fail w/ -EBUSY"
* 'for-3.19-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
cgroup: prevent mount hang due to memory controller lifetime
