cgroup: Disallow mounting v1 hierarchies without controller implementation

The configs that disable some v1 controllers would still allow mounting
them but with no controller-specific files. (Making such hierarchies
equivalent to named v1 hierarchies.) To achieve behavior consistent with
actual out-compilation of a whole controller, the mounts should treat
respective controllers as non-existent.

Wrap implementation into a helper function, leverage legacy_files to
detect compiled out controllers. The effect is that mounts on v1 would
fail and produce a message like:
  [ 1543.999081] cgroup: Unknown subsys name 'memory'

Signed-off-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index b9dbf6bf2779d684d29122dbebd40fc40d67e3a1..784337694a4be084c31fed89031959495096448b 100644 (file)
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -46,6 +46,12 @@ bool cgroup1_ssid_disabled(int ssid)
        return cgroup_no_v1_mask & (1 << ssid);
 }
 
+static bool cgroup1_subsys_absent(struct cgroup_subsys *ss)
+{
+       /* Check also dfl_cftypes for file-less controllers, i.e. perf_event */
+       return ss->legacy_cftypes == NULL && ss->dfl_cftypes;
+}
+
 /**
  * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
  * @from: attach to all cgroups of a given task
@@ -932,7 +938,8 @@ int cgroup1_parse_param(struct fs_context *fc, struct fs_parameter *param)
                if (ret != -ENOPARAM)
                        return ret;
                for_each_subsys(ss, i) {
-                       if (strcmp(param->key, ss->legacy_name))
+                       if (strcmp(param->key, ss->legacy_name) ||
+                           cgroup1_subsys_absent(ss))
                                continue;
                        if (!cgroup_ssid_enabled(i) || cgroup1_ssid_disabled(i))
                                return invalfc(fc, "Disabled controller '%s'",
@@ -1024,7 +1031,8 @@ static int check_cgroupfs_options(struct fs_context *fc)
        mask = ~((u16)1 << cpuset_cgrp_id);
 #endif
        for_each_subsys(ss, i)
-               if (cgroup_ssid_enabled(i) && !cgroup1_ssid_disabled(i))
+               if (cgroup_ssid_enabled(i) && !cgroup1_ssid_disabled(i) &&
+                   !cgroup1_subsys_absent(ss))
                        enabled |= 1 << i;
 
        ctx->subsys_mask &= enabled;