9 files changed, 85 insertions, 2 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index f3b44a65fc7a..cafcd7431189 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -737,6 +737,14 @@ struct cgroup_subsys blkio_subsys = {
         .subsys_id = blkio_subsys_id,
         .base_cftypes = blkcg_files,
         .module = THIS_MODULE,
+
+        /*
+         * blkio subsystem is utterly broken in terms of hierarchy support.
+         * It treats all cgroups equally regardless of where they're
+         * located in the hierarchy - all cgroups are treated as if they're
+         * right below the root.  Fix it and remove the following.
+         */
+        .broken_hierarchy = true,
 };
 EXPORT_SYMBOL_GPL(blkio_subsys);
 
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index c90eaa803440..68e8df70487e 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -496,6 +496,21 @@ struct cgroup_subsys {
          */
         bool __DEPRECATED_clear_css_refs;
 
+        /*
+         * If %false, this subsystem is properly hierarchical -
+         * configuration, resource accounting and restriction on a parent
+         * cgroup cover those of its children.  If %true, hierarchy support
+         * is broken in some ways - some subsystems ignore hierarchy
+         * completely while others are only implemented half-way.
+         *
+         * It's now disallowed to create nested cgroups if the subsystem is
+         * broken and cgroup core will emit a warning message on such
+         * cases.  Eventually, all subsystems will be made properly
+         * hierarchical and this will go away.
+         */
+        bool broken_hierarchy;
+        bool warned_broken_hierarchy;
+
 #define MAX_CGROUP_TYPE_NAMELEN 32
         const char *name;
 
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 79818507e444..b7d9606b17d7 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3954,8 +3954,9 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
                 set_bit(CGRP_CLONE_CHILDREN, &cgrp->flags);
 
         for_each_subsys(root, ss) {
-                struct cgroup_subsys_state *css = ss->create(cgrp);
+                struct cgroup_subsys_state *css;
 
+                css = ss->create(cgrp);
                 if (IS_ERR(css)) {
                         err = PTR_ERR(css);
                         goto err_destroy;
@@ -3969,6 +3970,15 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
                 /* At error, ->destroy() callback has to free assigned ID. */
                 if (clone_children(parent) && ss->post_clone)
                         ss->post_clone(cgrp);
+
+                if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
+                    parent->parent) {
+                        pr_warning("cgroup: %s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
+                                   current->comm, current->pid, ss->name);
+                        if (!strcmp(ss->name, "memory"))
+                                pr_warning("cgroup: \"memory\" requires setting use_hierarchy to 1 on the root.\n");
+                        ss->warned_broken_hierarchy = true;
+                }
         }
 
         list_add(&cgrp->sibling, &cgrp->parent->children);
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 3649fc6b3eaa..b1724ce98981 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -373,4 +373,12 @@ struct cgroup_subsys freezer_subsys = {
         .can_attach     = freezer_can_attach,
         .fork           = freezer_fork,
         .base_cftypes   = files,
+
+        /*
+         * freezer subsys doesn't handle hierarchy at all.  Frozen state
+         * should be inherited through the hierarchy - if a parent is
+         * frozen, all its children should be frozen.  Fix it and remove
+         * the following.
+         */
+        .broken_hierarchy = true,
 };
diff --git a/kernel/events/core.c b/kernel/events/core.c
index b7935fcec7d9..f18a0a56e5aa 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7285,5 +7285,12 @@ struct cgroup_subsys perf_subsys = {
         .destroy        = perf_cgroup_destroy,
         .exit           = perf_cgroup_exit,
         .attach         = perf_cgroup_attach,
+
+        /*
+         * perf_event cgroup doesn't handle nesting correctly.
+         * ctx->nr_cgroups adjustments should be propagated through the
+         * cgroup hierarchy.  Fix it and remove the following.
+         */
+        .broken_hierarchy = true,
 };
 #endif /* CONFIG_CGROUP_PERF */
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 795e525afaba..a72f2ffdc3d0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4973,6 +4973,13 @@ mem_cgroup_create(struct cgroup *cont)
         } else {
                 res_counter_init(&memcg->res, NULL);
                 res_counter_init(&memcg->memsw, NULL);
+                /*
+                 * Deeper hierachy with use_hierarchy == false doesn't make
+                 * much sense so let cgroup subsystem know about this
+                 * unfortunate state in our controller.
+                 */
+                if (parent && parent != root_mem_cgroup)
+                        mem_cgroup_subsys.broken_hierarchy = true;
         }
         memcg->last_scanned_node = MAX_NUMNODES;
         INIT_LIST_HEAD(&memcg->oom_notify);
diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c
index c75e3f9d060f..34f3615b30ca 100644
--- a/net/core/netprio_cgroup.c
+++ b/net/core/netprio_cgroup.c
@@ -330,7 +330,17 @@ struct cgroup_subsys net_prio_subsys = {
         .subsys_id      = net_prio_subsys_id,
 #endif
         .base_cftypes   = ss_files,
-        .module         = THIS_MODULE
+        .module         = THIS_MODULE,
+
+        /*
+         * net_prio has artificial limit on the number of cgroups and
+         * disallows nesting making it impossible to co-mount it with other
+         * hierarchical subsystems.  Remove the artificially low PRIOIDX_SZ
+         * limit and properly nest configuration such that children follow
+         * their parents' configurations by default and are allowed to
+         * override and remove the following.
+         */
+        .broken_hierarchy = true,
 };
 
 static int netprio_device_event(struct notifier_block *unused,
diff --git a/net/sched/cls_cgroup.c b/net/sched/cls_cgroup.c
index 7743ea8d1d38..907daf99ab2e 100644
--- a/net/sched/cls_cgroup.c
+++ b/net/sched/cls_cgroup.c
@@ -82,6 +82,15 @@ struct cgroup_subsys net_cls_subsys = {
 #endif
         .base_cftypes   = ss_files,
         .module         = THIS_MODULE,
+
+        /*
+         * While net_cls cgroup has the rudimentary hierarchy support of
+         * inheriting the parent's classid on cgroup creation, it doesn't
+         * properly propagates config changes in ancestors to their
+         * descendents.  A child should follow the parent's configuration
+         * but be allowed to override it.  Fix it and remove the following.
+         */
+        .broken_hierarchy = true,
 };
 
 struct cls_cgroup_head {
diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 442204cc22d9..4b877a92a7ea 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -457,6 +457,15 @@ struct cgroup_subsys devices_subsys = {
         .destroy = devcgroup_destroy,
         .subsys_id = devices_subsys_id,
         .base_cftypes = dev_cgroup_files,
+
+        /*
+         * While devices cgroup has the rudimentary hierarchy support which
+         * checks the parent's restriction, it doesn't properly propagates
+         * config changes in ancestors to their descendents.  A child
+         * should only be allowed to add more restrictions to the parent's
+         * configuration.  Fix it and remove the following.
+         */
+        .broken_hierarchy = true,
 };
 
 int __devcgroup_inode_permission(struct inode *inode, int mask)