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 <[email protected]>
Cc: Li Zefan <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: [email protected]
---
 kernel/cgroup.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f89d929..6c85e6d 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1332,9 +1332,10 @@ 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)
@@ -5136,9 +5137,11 @@ 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);
-- 
2.4.3

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