[PATCH v4 2/5] cgroup: add helper for checking when css is cgroup::self

[JP Kobryn <inwardvessel@gmail.com>]

The cgroup struct has a css field called "self". The main difference
between this css and the others found in the cgroup::subsys array is that
cgroup::self has a NULL subsystem pointer. There are several places where
checks are performed to determine whether the css in question is
cgroup::self or not. Instead of accessing css->ss directly, introduce a
helper function that shows the intent and use where applicable.

Signed-off-by: JP Kobryn <inwardvessel@gmail.com>
---
 include/linux/cgroup.h | 5 +++++
 kernel/cgroup/cgroup.c | 4 ++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 28e999f2c642..7c120efd5e49 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -347,6 +347,11 @@ static inline bool css_is_dying(struct cgroup_subsys_state *css)
 	return !(css->flags & CSS_NO_REF) && percpu_ref_is_dying(&css->refcnt);
 }
 
+static inline bool css_is_cgroup(struct cgroup_subsys_state *css)
+{
+	return css->ss == NULL;
+}
+
 static inline void cgroup_get(struct cgroup *cgrp)
 {
 	css_get(&cgrp->self);
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 77349d07b117..00eb882dc6e7 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1719,7 +1719,7 @@ static void css_clear_dir(struct cgroup_subsys_state *css)
 
 	css->flags &= ~CSS_VISIBLE;
 
-	if (!css->ss) {
+	if (css_is_cgroup(css)) {
 		if (cgroup_on_dfl(cgrp)) {
 			cgroup_addrm_files(css, cgrp,
 					   cgroup_base_files, false);
@@ -1751,7 +1751,7 @@ static int css_populate_dir(struct cgroup_subsys_state *css)
 	if (css->flags & CSS_VISIBLE)
 		return 0;
 
-	if (!css->ss) {
+	if (css_is_cgroup(css)) {
 		if (cgroup_on_dfl(cgrp)) {
 			ret = cgroup_addrm_files(css, cgrp,
 						 cgroup_base_files, true);
-- 
2.47.1