linux-kernel - [PATCH v2 2/2] include/cgroup: separate {get,put}_cgroup

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Message-ID: <20250508184930.183040-3-jsavitz@redhat.com>
Date: Thu,  8 May 2025 14:49:30 -0400
From: Joel Savitz <jsavitz@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: Joel Savitz <jsavitz@...hat.com>,
	Tejun Heo <tj@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Koutný <mkoutny@...e.com>,
	Christian Brauner <brauner@...nel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	cgroups@...r.kernel.org
Subject: [PATCH v2 2/2] include/cgroup: separate {get,put}_cgroup_ns no-op case

When CONFIG_CGROUPS is not selected, {get,put}_cgroup_ns become no-ops
and therefore it is not necessary to compile in the code for changing
the reference count.

When CONFIG_CGROUP is selected, there is no valid case where
either of {get,put}_cgroup_ns() will be called with a NULL argument.

Signed-off-by: Joel Savitz <jsavitz@...hat.com>
---
 include/linux/cgroup.h | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index e7da3c3b098b..166d6de50dbf 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -785,6 +785,17 @@ struct cgroup_namespace *copy_cgroup_ns(unsigned long flags,
 int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
 		   struct cgroup_namespace *ns);
 
+static inline void get_cgroup_ns(struct cgroup_namespace *ns)
+{
+	refcount_inc(&ns->ns.count);
+}
+
+static inline void put_cgroup_ns(struct cgroup_namespace *ns)
+{
+	if (refcount_dec_and_test(&ns->ns.count))
+		free_cgroup_ns(ns);
+}
+
 #else /* !CONFIG_CGROUPS */
 
 static inline void free_cgroup_ns(struct cgroup_namespace *ns) { }
@@ -795,19 +806,10 @@ copy_cgroup_ns(unsigned long flags, struct user_namespace *user_ns,
 	return old_ns;
 }
 
-#endif /* !CONFIG_CGROUPS */
+static inline void get_cgroup_ns(struct cgroup_namespace *ns) { }
+static inline void put_cgroup_ns(struct cgroup_namespace *ns) { }
 
-static inline void get_cgroup_ns(struct cgroup_namespace *ns)
-{
-	if (ns)
-		refcount_inc(&ns->ns.count);
-}
-
-static inline void put_cgroup_ns(struct cgroup_namespace *ns)
-{
-	if (ns && refcount_dec_and_test(&ns->ns.count))
-		free_cgroup_ns(ns);
-}
+#endif /* !CONFIG_CGROUPS */
 
 #ifdef CONFIG_CGROUPS
 
-- 
2.45.2