cgroup: don't print subsystems for the default hierarchy

It doesn't make sense to print subsystems on mount option or
/proc/PID/cgroup for the default hierarchy.

* cgroup.controllers file at the root of the default hierarchy lists
  the currently attached controllers.

* The default hierarchy is catch-all for unmounted subsystems.

* The default hierarchy doesn't accept any mount options.

Suppress subsystem printing on mount options and /proc/PID/cgroup for
the default hierarchy.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: cgroups@vger.kernel.org

1 files changed, 9 insertions, 6 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 3f6641632f73..d9f854defa78 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1333,9 +1333,10 @@ static int cgroup_show_options(struct seq_file *seq,
         struct cgroup_subsys *ss;
         int ssid;
 
-        for_each_subsys(ss, ssid)
-                if (root->subsys_mask & (1 << ssid))
-                        seq_printf(seq, ",%s", ss->name);
+        if (root != &cgrp_dfl_root)
+                for_each_subsys(ss, ssid)
+                        if (root->subsys_mask & (1 << ssid))
+                                seq_printf(seq, ",%s", ss->name);
         if (root->flags & CGRP_ROOT_NOPREFIX)
                 seq_puts(seq, ",noprefix");
         if (root->flags & CGRP_ROOT_XATTR)
@@ -5137,9 +5138,11 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
                         continue;
 
                 seq_printf(m, "%d:", root->hierarchy_id);
-                for_each_subsys(ss, ssid)
-                        if (root->subsys_mask & (1 << ssid))
-                                seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
+                if (root != &cgrp_dfl_root)
+                        for_each_subsys(ss, ssid)
+                                if (root->subsys_mask & (1 << ssid))
+                                        seq_printf(m, "%s%s", count++ ? "," : "",
+                                                   ss->name);
                 if (strlen(root->name))
                         seq_printf(m, "%sname=%s", count ? "," : "",
                                    root->name);