cgroup: disallow xattr, release_agent and name if sane_behavior

Disallow more mount options if sane_behavior.  Note that xattr used to
generate warning.

While at it, simplify option check in cgroup_mount() and update
sane_behavior comment in cgroup.h.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>

include/linux/cgroup.h

@@ -227,8 +227,8 @@ enum {
 	 *
 	 * The followings are the behaviors currently affected this flag.
 	 *
-	 * - Mount options "noprefix" and "clone_children" are disallowed.
-	 *   Also, cgroupfs file cgroup.clone_children is not created.
+	 * - Mount options "noprefix", "xattr", "clone_children",
+	 *   "release_agent" and "name" are disallowed.
 	 *
 	 * - When mounting an existing superblock, mount options should
 	 *   match.
@@ -246,7 +246,7 @@ enum {
 	 * - "release_agent" and "notify_on_release" are removed.
 	 *   Replacement notification mechanism will be implemented.
 	 *
-	 * - "xattr" mount option is deprecated.  kernfs always enables it.
+	 * - "cgroup.clone_children" is removed.
 	 *
 	 * - cpuset: tasks will be kept in empty cpusets when hotplug happens
 	 *   and take masks of ancestors with non-empty cpus/mems, instead of

kernel/cgroup.c

@@ -1226,18 +1226,12 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
 	if (opts->flags & CGRP_ROOT_SANE_BEHAVIOR) {
 		pr_warning("cgroup: sane_behavior: this is still under development and its behaviors will change, proceed at your own risk\n");
 
-		if (opts->flags & CGRP_ROOT_NOPREFIX) {
-			pr_err("cgroup: sane_behavior: noprefix is not allowed\n");
+		if ((opts->flags & (CGRP_ROOT_NOPREFIX | CGRP_ROOT_XATTR)) ||
+		    opts->cpuset_clone_children || opts->release_agent ||
+		    opts->name) {
+			pr_err("cgroup: sane_behavior: noprefix, xattr, clone_children, release_agent and name are not allowed\n");
 			return -EINVAL;
 		}
-
-		if (opts->cpuset_clone_children) {
-			pr_err("cgroup: sane_behavior: clone_children is not allowed\n");
-			return -EINVAL;
-		}
-
-		if (opts->flags & CGRP_ROOT_XATTR)
-			pr_warning("cgroup: sane_behavior: xattr is always available, flag unnecessary\n");
 	}
 
 	/*