[PATCH] cgroup: Introduce css_is_online() helper

[Xiu Jianfeng <xiujianfeng@huawei.com>]

Introduce css_is_online() helper to test if whether the specified
css is online, avoid testing css.flags with CSS_ONLINE directly
outside of cgroup.c.

Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
---
 fs/fs-writeback.c               | 2 +-
 include/linux/cgroup.h          | 9 +++++++++
 include/linux/memcontrol.h      | 2 +-
 kernel/cgroup/cgroup-internal.h | 2 +-
 mm/memcontrol.c                 | 2 +-
 mm/page_owner.c                 | 2 +-
 6 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 92a5b8283528..bb84c6a2fa8e 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -916,7 +916,7 @@ void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,
 	folio = page_folio(page);
 	css = mem_cgroup_css_from_folio(folio);
 	/* dead cgroups shouldn't contribute to inode ownership arbitration */
-	if (!(css->flags & CSS_ONLINE))
+	if (!css_is_online(css))
 		return;
 
 	id = css->id;
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 2150ca60394b..e6b6f3418da8 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -346,6 +346,15 @@ static inline bool css_is_dying(struct cgroup_subsys_state *css)
 	return !(css->flags & CSS_NO_REF) && percpu_ref_is_dying(&css->refcnt);
 }
 
+/*
+ * css_is_online - test whether the specified css is online
+ * @css: target css
+ */
+static inline bool css_is_online(struct cgroup_subsys_state *css)
+{
+	return !!(css->flags & CSS_ONLINE);
+}
+
 static inline void cgroup_get(struct cgroup *cgrp)
 {
 	css_get(&cgrp->self);
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 8f332b4ae84c..cd6b3bfd070f 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -939,7 +939,7 @@ static inline bool mem_cgroup_online(struct mem_cgroup *memcg)
 {
 	if (mem_cgroup_disabled())
 		return true;
-	return !!(memcg->css.flags & CSS_ONLINE);
+	return css_is_online(&memcg->css);
 }
 
 void mem_cgroup_update_lru_size(struct lruvec *lruvec, enum lru_list lru,
diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index 520b90dd97ec..feeaf172844d 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -183,7 +183,7 @@ extern struct list_head cgroup_roots;
 
 static inline bool cgroup_is_dead(const struct cgroup *cgrp)
 {
-	return !(cgrp->self.flags & CSS_ONLINE);
+	return !css_is_online(&cgrp->self);
 }
 
 static inline bool notify_on_release(const struct cgroup *cgrp)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7703ced535a3..e77e9e1911e6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -405,7 +405,7 @@ ino_t page_cgroup_ino(struct page *page)
 	/* page_folio() is racy here, but the entire function is racy anyway */
 	memcg = folio_memcg_check(page_folio(page));
 
-	while (memcg && !(memcg->css.flags & CSS_ONLINE))
+	while (memcg && !css_is_online(&memcg->css))
 		memcg = parent_mem_cgroup(memcg);
 	if (memcg)
 		ino = cgroup_ino(memcg->css.cgroup);
diff --git a/mm/page_owner.c b/mm/page_owner.c
index 75c23302868a..7accb25e6fe6 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -523,7 +523,7 @@ static inline int print_page_owner_memcg(char *kbuf, size_t count, int ret,
 	if (!memcg)
 		goto out_unlock;
 
-	online = (memcg->css.flags & CSS_ONLINE);
+	online = css_is_online(&memcg->css);
 	cgroup_name(memcg->css.cgroup, name, sizeof(name));
 	ret += scnprintf(kbuf + ret, count - ret,
 			"Charged %sto %smemcg %s\n",
-- 
2.34.1