cgroup: Print message when /proc/cgroups is read on v2-only system

As a followup to commits 6c2920926b10e ("cgroup: replace
unified-hierarchy.txt with a proper cgroup v2 documentation") and
ab03125268679 ("cgroup: Show # of subsystem CSSes in cgroup.stat"),
add a runtime message to users who read status of controllers in
/proc/cgroups on v2-only system. The detection is based on a)
no controllers are attached to v1, b) default hierarchy is mounted (the
latter is for setups that never mount v2 but read /proc/cgroups upon
boot when controllers default to v2, so that this code may be backported
to older kernels).

Signed-off-by: Michal Koutný <mkoutny@suse.com>
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index c964dd7ff967a030b5e1aed3c543e82efc20aa0f..95ab39e1ec8f0b5d675435ff170a2a0b2080bbd3 100644 (file)
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -168,6 +168,7 @@ struct cgroup_mgctx {
 
 extern struct cgroup_subsys *cgroup_subsys[];
 extern struct list_head cgroup_roots;
+extern bool cgrp_dfl_visible;
 
 /* iterate across the hierarchies */
 #define for_each_root(root)                                            \

diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index e28d5f0d20ed09e439b98bd21c83995bc0e55242..11ea8d24ac727534803ea3428a1383c054ea32d6 100644 (file)
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -673,6 +673,7 @@ struct cftype cgroup1_base_files[] = {
 int proc_cgroupstats_show(struct seq_file *m, void *v)
 {
        struct cgroup_subsys *ss;
+       bool cgrp_v1_visible = false;
        int i;
 
        seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
@@ -684,12 +685,18 @@ int proc_cgroupstats_show(struct seq_file *m, void *v)
        for_each_subsys(ss, i) {
                if (cgroup1_subsys_absent(ss))
                        continue;
+               cgrp_v1_visible |= ss->root != &cgrp_dfl_root;
+
                seq_printf(m, "%s\t%d\t%d\t%d\n",
                           ss->legacy_name, ss->root->hierarchy_id,
                           atomic_read(&ss->root->nr_cgrps),
                           cgroup_ssid_enabled(i));
        }
 
+       if (cgrp_dfl_visible && !cgrp_v1_visible)
+               pr_info_once("/proc/cgroups lists only v1 controllers, use cgroup.controllers of root cgroup for v2 info\n");
+
+
        return 0;
 }
 

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 805764cf14e2ff4c66e9895574c05d06ee3cbce5..a810952d75c843698d03ecdbd95d325acaae0782 100644 (file)
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -171,7 +171,7 @@ EXPORT_SYMBOL_GPL(cgrp_dfl_root);
  * The default hierarchy always exists but is hidden until mounted for the
  * first time.  This is for backward compatibility.
  */
-static bool cgrp_dfl_visible;
+bool cgrp_dfl_visible;
 
 /* some controllers are not supported in the default hierarchy */
 static u16 cgrp_dfl_inhibit_ss_mask;