cgroup: Add mount flag to enable cpuset to use v2 behavior in v1 cgroup

A new mount option "cpuset_v2_mode" is added to the v1 cgroupfs
filesystem to enable cpuset controller to use v2 behavior in a v1
cgroup. This mount option applies only to cpuset controller and have
no effect on other controllers.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

2 files changed, 11 insertions, 0 deletions

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 59e4ad9e7bac..ade4a78a54c2 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -74,6 +74,11 @@ enum {
          * aren't writeable from inside the namespace.
          */
         CGRP_ROOT_NS_DELEGATE   = (1 << 3),
+
+        /*
+         * Enable cpuset controller in v1 cgroup to use v2 behavior.
+         */
+        CGRP_ROOT_CPUSET_V2_MODE = (1 << 4),
 };
 
 /* cftype->flags */
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index f0e8601b13cb..024085daab1a 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -895,6 +895,8 @@ static int cgroup1_show_options(struct seq_file *seq, struct kernfs_root *kf_roo
                 seq_puts(seq, ",noprefix");
         if (root->flags & CGRP_ROOT_XATTR)
                 seq_puts(seq, ",xattr");
+        if (root->flags & CGRP_ROOT_CPUSET_V2_MODE)
+                seq_puts(seq, ",cpuset_v2_mode");
 
         spin_lock(&release_agent_path_lock);
         if (strlen(root->release_agent_path))
@@ -949,6 +951,10 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
                         opts->cpuset_clone_children = true;
                         continue;
                 }
+                if (!strcmp(token, "cpuset_v2_mode")) {
+                        opts->flags |= CGRP_ROOT_CPUSET_V2_MODE;
+                        continue;
+                }
                 if (!strcmp(token, "xattr")) {
                         opts->flags |= CGRP_ROOT_XATTR;
                         continue;