1 files changed, 56 insertions, 44 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 78017f52c69b..b632981bd9c7 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -175,8 +175,8 @@ static int need_forkexit_callback __read_mostly;
 static struct cftype cgroup_base_files[];
 
 static void cgroup_put(struct cgroup *cgrp);
-static int rebind_subsystems(struct cgroupfs_root *root,
-                             unsigned long added_mask, unsigned removed_mask);
+static int rebind_subsystems(struct cgroupfs_root *dst_root,
+                             unsigned long ss_mask);
 static void cgroup_destroy_css_killed(struct cgroup *cgrp);
 static int cgroup_destroy_locked(struct cgroup *cgrp);
 static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
@@ -739,7 +739,7 @@ static void cgroup_destroy_root(struct cgroupfs_root *root)
         BUG_ON(!list_empty(&cgrp->children));
 
         /* Rebind all subsystems back to the default hierarchy */
-        WARN_ON(rebind_subsystems(root, 0, root->subsys_mask));
+        rebind_subsystems(&cgroup_dummy_root, root->subsys_mask);
 
         /*
          * Release all the links from cset_links to this hierarchy's
@@ -976,69 +976,77 @@ static void cgroup_clear_dir(struct cgroup *cgrp, unsigned long subsys_mask)
         }
 }
 
-static int rebind_subsystems(struct cgroupfs_root *root,
-                             unsigned long added_mask, unsigned removed_mask)
+static int rebind_subsystems(struct cgroupfs_root *dst_root,
+                             unsigned long ss_mask)
 {
-        struct cgroup *cgrp = &root->top_cgroup;
+        struct cgroup *dst_top = &dst_root->top_cgroup;
         struct cgroup_subsys *ss;
-        int i, ret;
+        int ssid, ret;
 
         lockdep_assert_held(&cgroup_tree_mutex);
         lockdep_assert_held(&cgroup_mutex);
 
-        /* Check that any added subsystems are currently free */
-        for_each_subsys(ss, i)
-                if ((added_mask & (1 << i)) && ss->root != &cgroup_dummy_root)
+        for_each_subsys(ss, ssid) {
+                if (!(ss_mask & (1 << ssid)))
+                        continue;
+
+                /* if @ss is on the dummy_root, we can always move it */
+                if (ss->root == &cgroup_dummy_root)
+                        continue;
+
+                /* if @ss has non-root cgroups attached to it, can't move */
+                if (!list_empty(&ss->root->top_cgroup.children))
                         return -EBUSY;
 
-        ret = cgroup_populate_dir(cgrp, added_mask);
-        if (ret)
-                return ret;
+                /* can't move between two non-dummy roots either */
+                if (dst_root != &cgroup_dummy_root)
+                        return -EBUSY;
+        }
+
+        if (dst_root != &cgroup_dummy_root) {
+                ret = cgroup_populate_dir(dst_top, ss_mask);
+                if (ret)
+                        return ret;
+        }
 
         /*
          * Nothing can fail from this point on.  Remove files for the
          * removed subsystems and rebind each subsystem.
          */
         mutex_unlock(&cgroup_mutex);
-        cgroup_clear_dir(cgrp, removed_mask);
+        for_each_subsys(ss, ssid)
+                if ((ss_mask & (1 << ssid)) && ss->root != &cgroup_dummy_root)
+                        cgroup_clear_dir(&ss->root->top_cgroup, 1 << ssid);
         mutex_lock(&cgroup_mutex);
 
-        for_each_subsys(ss, i) {
-                unsigned long bit = 1UL << i;
-
-                if (bit & added_mask) {
-                        /* We're binding this subsystem to this hierarchy */
-                        BUG_ON(cgroup_css(cgrp, ss));
-                        BUG_ON(!cgroup_css(cgroup_dummy_top, ss));
-                        BUG_ON(cgroup_css(cgroup_dummy_top, ss)->cgroup != cgroup_dummy_top);
+        for_each_subsys(ss, ssid) {
+                struct cgroupfs_root *src_root;
+                struct cgroup *src_top;
+                struct cgroup_subsys_state *css;
 
-                        rcu_assign_pointer(cgrp->subsys[i],
-                                           cgroup_css(cgroup_dummy_top, ss));
-                        cgroup_css(cgrp, ss)->cgroup = cgrp;
+                if (!(ss_mask & (1 << ssid)))
+                        continue;
 
-                        ss->root = root;
-                        if (ss->bind)
-                                ss->bind(cgroup_css(cgrp, ss));
+                src_root = ss->root;
+                src_top = &src_root->top_cgroup;
+                css = cgroup_css(src_top, ss);
 
-                        /* refcount was already taken, and we're keeping it */
-                        root->subsys_mask |= bit;
-                } else if (bit & removed_mask) {
-                        /* We're removing this subsystem */
-                        BUG_ON(cgroup_css(cgrp, ss) != cgroup_css(cgroup_dummy_top, ss));
-                        BUG_ON(cgroup_css(cgrp, ss)->cgroup != cgrp);
+                WARN_ON(!css || cgroup_css(dst_top, ss));
 
-                        if (ss->bind)
-                                ss->bind(cgroup_css(cgroup_dummy_top, ss));
+                RCU_INIT_POINTER(src_top->subsys[ssid], NULL);
+                rcu_assign_pointer(dst_top->subsys[ssid], css);
+                ss->root = dst_root;
+                css->cgroup = dst_top;
 
-                        cgroup_css(cgroup_dummy_top, ss)->cgroup = cgroup_dummy_top;
-                        RCU_INIT_POINTER(cgrp->subsys[i], NULL);
+                src_root->subsys_mask &= ~(1 << ssid);
+                dst_root->subsys_mask |= 1 << ssid;
 
-                        cgroup_subsys[i]->root = &cgroup_dummy_root;
-                        root->subsys_mask &= ~bit;
-                }
+                if (ss->bind)
+                        ss->bind(css);
         }
 
-        kernfs_activate(cgrp->kn);
+        if (dst_root != &cgroup_dummy_root)
+                kernfs_activate(dst_top->kn);
         return 0;
 }
 
@@ -1277,10 +1285,12 @@ static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
                 goto out_unlock;
         }
 
-        ret = rebind_subsystems(root, added_mask, removed_mask);
+        ret = rebind_subsystems(root, added_mask);
         if (ret)
                 goto out_unlock;
 
+        rebind_subsystems(&cgroup_dummy_root, removed_mask);
+
         if (opts.release_agent) {
                 spin_lock(&release_agent_path_lock);
                 strcpy(root->release_agent_path, opts.release_agent);
@@ -1420,7 +1430,7 @@ static int cgroup_setup_root(struct cgroupfs_root *root, unsigned long ss_mask)
         if (ret)
                 goto destroy_root;
 
-        ret = rebind_subsystems(root, ss_mask, 0);
+        ret = rebind_subsystems(root, ss_mask);
         if (ret)
                 goto destroy_root;
 
@@ -4026,6 +4036,8 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
 
         BUG_ON(online_css(css));
 
+        cgroup_dummy_root.subsys_mask |= 1 << ss->id;
+
         mutex_unlock(&cgroup_mutex);
         mutex_unlock(&cgroup_tree_mutex);
 }