cgroup: move number_of_cgroups test out of rebind_subsystems() into cgroup_remount()

rebind_subsystems() currently fails if the hierarchy has any !root
cgroups; however, on the planned unified hierarchy,
rebind_subsystems() will be used while populated.  Move the test to
cgroup_remount(), which is the only place the test is necessary
anyway.

As it's impossible for the other two callers of rebind_subsystems() to
have populated hierarchy, this doesn't make any behavior changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>

1 files changed, 6 insertions, 7 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 4ec8d2da94d1..c108d3d1ea30 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1021,13 +1021,6 @@ static int rebind_subsystems(struct cgroupfs_root *root,
                 }
         }
 
-        /* Currently we don't handle adding/removing subsystems when
-         * any child cgroups exist. This is theoretically supportable
-         * but involves complex error handling, so it's being left until
-         * later */
-        if (root->number_of_cgroups > 1)
-                return -EBUSY;
-
         ret = cgroup_populate_dir(cgrp, added_mask);
         if (ret)
                 return ret;
@@ -1373,6 +1366,12 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
                 goto out_unlock;
         }
 
+        /* remounting is not allowed for populated hierarchies */
+        if (root->number_of_cgroups > 1) {
+                ret = -EBUSY;
+                goto out_unlock;
+        }
+
         ret = rebind_subsystems(root, added_mask, removed_mask);
         if (ret)
                 goto out_unlock;