[Devel] [PATCH RH9 4/4] cgroup: show and allow mounting of cgroup-v2 in containers

[Pavel Tikhomirov]

The change in is_virtualized_cgroot makes cgroup-v2 "virtualized" only
when it has enabled subsystems in it. And "virtualized" means that it
will be:
a) shown in different cgroup related proc files in container,
b) allowed to be mounted in container and
c) required to have separate root directory for container

Note: we don't expect cgroup-v2 root to change enabled controllers, it
either has no controllers or has at least one all the way.
Note: cgroup-v2 has one hierarchy for all controllers, so skipping misc
and debug for vzctl is not required anymore.

Add FS_VIRTUALIZED to cgroup2 to allow mounting in container.

https://jira.vzint.dev/browse/PSBM-149975
Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
 kernel/cgroup/cgroup.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 945130057a30..d902e675598d 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2060,18 +2060,16 @@ struct ve_struct *get_curr_ve(void)
  */
 static inline bool is_virtualized_cgroot(struct cgroup_root *cgroot)
 {
-	/* Cgroup v2 */
-	if (cgroot == &cgrp_dfl_root)
-		return false;
-
+	if (cgroot != &cgrp_dfl_root) {
 #if IS_ENABLED(CONFIG_CGROUP_DEBUG)
-	if (cgroot->subsys_mask & (1 << debug_cgrp_id))
-		return false;
+		if (cgroot->subsys_mask & (1 << debug_cgrp_id))
+			return false;
 #endif
 #if IS_ENABLED(CONFIG_CGROUP_MISC)
-	if (cgroot->subsys_mask & (1 << misc_cgrp_id))
-		return false;
+		if (cgroot->subsys_mask & (1 << misc_cgrp_id))
+			return false;
 #endif
+	}
 
 	if (cgroot->subsys_mask)
 		return true;
@@ -2628,7 +2626,7 @@ static struct file_system_type cgroup2_fs_type = {
 	.init_fs_context	= cgroup_init_fs_context,
 	.parameters		= cgroup2_fs_parameters,
 	.kill_sb		= cgroup_kill_sb,
-	.fs_flags		= FS_USERNS_MOUNT,
+	.fs_flags		= FS_USERNS_MOUNT | FS_VIRTUALIZED,
 };
 
 #ifdef CONFIG_CPUSETS
-- 
2.41.0