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cgroup: mark subsystems with broken hierarchy support and whine if cg…
…roups are nested for them Currently, cgroup hierarchy support is a mess. cpu related subsystems behave correctly - configuration, accounting and control on a parent properly cover its children. blkio and freezer completely ignore hierarchy and treat all cgroups as if they're directly under the root cgroup. Others show yet different behaviors. These differing interpretations of cgroup hierarchy make using cgroup confusing and it impossible to co-mount controllers into the same hierarchy and obtain sane behavior. Eventually, we want full hierarchy support from all subsystems and probably a unified hierarchy. Users using separate hierarchies expecting completely different behaviors depending on the mounted subsystem is deterimental to making any progress on this front. This patch adds cgroup_subsys.broken_hierarchy and sets it to %true for controllers which are lacking in hierarchy support. The goal of this patch is two-fold. * Move users away from using hierarchy on currently non-hierarchical subsystems, so that implementing proper hierarchy support on those doesn't surprise them. * Keep track of which controllers are broken how and nudge the subsystems to implement proper hierarchy support. For now, start with a single warning message. We can whine louder later on. v2: Fixed a typo spotted by Michal. Warning message updated. v3: Updated memcg part so that it doesn't generate warning in the cases where .use_hierarchy=false doesn't make the behavior different from root.use_hierarchy=true. Fixed a typo spotted by Glauber. v4: Check ->broken_hierarchy after cgroup creation is complete so that ->create() can affect the result per Michal. Dropped unnecessary memcg root handling per Michal. Signed-off-by: Tejun Heo <email@example.com> Acked-by: Michal Hocko <firstname.lastname@example.org> Acked-by: Li Zefan <email@example.com> Acked-by: Serge E. Hallyn <firstname.lastname@example.org> Cc: Glauber Costa <email@example.com> Cc: Peter Zijlstra <firstname.lastname@example.org> Cc: Paul Turner <email@example.com> Cc: Johannes Weiner <firstname.lastname@example.org> Cc: Thomas Graf <email@example.com> Cc: Vivek Goyal <firstname.lastname@example.org> Cc: Paul Mackerras <email@example.com> Cc: Ingo Molnar <firstname.lastname@example.org> Cc: Arnaldo Carvalho de Melo <email@example.com> Cc: Neil Horman <firstname.lastname@example.org> Cc: Aneesh Kumar K.V <email@example.com>
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