cgroup: compare css to cgroup::self in helper for distingushing css

Adjust the implementation of css_is_cgroup() so that it compares the given
css to cgroup::self. Rename the function to css_is_self() in order to
reflect that. Change the existing css->ss NULL check to a warning in the
true branch. Finally, adjust call sites to use the new function name.

Signed-off-by: JP Kobryn <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>

Author: inwardvessel

include/linux/cgroup.h

@@ -347,9 +347,15 @@ static inline bool css_is_dying(struct cgroup_subsys_state *css)
 	return css->flags & CSS_DYING;
 }
 
-static inline bool css_is_cgroup(struct cgroup_subsys_state *css)
+static inline bool css_is_self(struct cgroup_subsys_state *css)
 {
-	return css->ss == NULL;
+	if (css == &css->cgroup->self) {
+		/* cgroup::self should not have subsystem association */
+		WARN_ON(css->ss != NULL);
+		return true;
+	}
+
+	return false;
 }
 
 static inline void cgroup_get(struct cgroup *cgrp)

kernel/cgroup/cgroup.c

@@ -1706,7 +1706,7 @@ static void css_clear_dir(struct cgroup_subsys_state *css)
 
 	css->flags &= ~CSS_VISIBLE;
 
-	if (css_is_cgroup(css)) {
+	if (css_is_self(css)) {
 		if (cgroup_on_dfl(cgrp)) {
 			cgroup_addrm_files(css, cgrp,
 					   cgroup_base_files, false);
@@ -1738,7 +1738,7 @@ static int css_populate_dir(struct cgroup_subsys_state *css)
 	if (css->flags & CSS_VISIBLE)
 		return 0;
 
-	if (css_is_cgroup(css)) {
+	if (css_is_self(css)) {
 		if (cgroup_on_dfl(cgrp)) {
 			ret = cgroup_addrm_files(css, cgrp,
 						 cgroup_base_files, true);
@@ -5406,7 +5406,7 @@ static void css_free_rwork_fn(struct work_struct *work)
 
 	percpu_ref_exit(&css->refcnt);
 
-	if (ss) {
+	if (!css_is_self(css)) {
 		/* css free path */
 		struct cgroup_subsys_state *parent = css->parent;
 		int id = css->id;
@@ -5460,7 +5460,7 @@ static void css_release_work_fn(struct work_struct *work)
 	css->flags |= CSS_RELEASED;
 	list_del_rcu(&css->sibling);
 
-	if (ss) {
+	if (!css_is_self(css)) {
 		struct cgroup *parent_cgrp;
 
 		/* css release path */