linux-kernel - [PATCH 01/14] ns: add reference count helpers

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Message-Id: <20250918-work-namespace-ns_ref-v1-1-1b0a98ee041e@kernel.org>
Date: Thu, 18 Sep 2025 12:11:46 +0200
From: Christian Brauner <brauner@...nel.org>
To: linux-fsdevel@...r.kernel.org
Cc: Amir Goldstein <amir73il@...il.com>, Josef Bacik <josef@...icpanda.com>, 
 Jeff Layton <jlayton@...nel.org>, Mike Yuan <me@...dnzj.com>, 
 Zbigniew Jędrzejewski-Szmek <zbyszek@...waw.pl>, 
 Lennart Poettering <mzxreary@...inter.de>, 
 Daan De Meyer <daan.j.demeyer@...il.com>, Aleksa Sarai <cyphar@...har.com>, 
 Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, 
 Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>, 
 Michal Koutný <mkoutny@...e.com>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Anna-Maria Behnsen <anna-maria@...utronix.de>, 
 Frederic Weisbecker <frederic@...nel.org>, 
 Thomas Gleixner <tglx@...utronix.de>, cgroups@...r.kernel.org, 
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
 Christian Brauner <brauner@...nel.org>
Subject: [PATCH 01/14] ns: add reference count helpers

Signed-off-by: Christian Brauner <brauner@...nel.org>
---
 include/linux/ns_common.h | 45 +++++++++++++++++++++++++++++++++++----------
 1 file changed, 35 insertions(+), 10 deletions(-)

diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h
index 5094c0147b54..a65da646aef7 100644
--- a/include/linux/ns_common.h
+++ b/include/linux/ns_common.h
@@ -43,16 +43,24 @@ struct ns_common {
 int __ns_common_init(struct ns_common *ns, const struct proc_ns_operations *ops, int inum);
 void __ns_common_free(struct ns_common *ns);
 
-#define to_ns_common(__ns)                              \
-	_Generic((__ns),                                \
-		struct cgroup_namespace *: &(__ns)->ns, \
-		struct ipc_namespace *:    &(__ns)->ns, \
-		struct mnt_namespace *:    &(__ns)->ns, \
-		struct net *:              &(__ns)->ns, \
-		struct pid_namespace *:    &(__ns)->ns, \
-		struct time_namespace *:   &(__ns)->ns, \
-		struct user_namespace *:   &(__ns)->ns, \
-		struct uts_namespace *:    &(__ns)->ns)
+#define to_ns_common(__ns)                                    \
+	_Generic((__ns),                                      \
+		struct cgroup_namespace *:       &(__ns)->ns, \
+		const struct cgroup_namespace *: &(__ns)->ns, \
+		struct ipc_namespace *:          &(__ns)->ns, \
+		const struct ipc_namespace *:    &(__ns)->ns, \
+		struct mnt_namespace *:          &(__ns)->ns, \
+		const struct mnt_namespace *:    &(__ns)->ns, \
+		struct net *:                    &(__ns)->ns, \
+		const struct net *:              &(__ns)->ns, \
+		struct pid_namespace *:          &(__ns)->ns, \
+		const struct pid_namespace *:    &(__ns)->ns, \
+		struct time_namespace *:         &(__ns)->ns, \
+		const struct time_namespace *:   &(__ns)->ns, \
+		struct user_namespace *:         &(__ns)->ns, \
+		const struct user_namespace *:   &(__ns)->ns, \
+		struct uts_namespace *:          &(__ns)->ns, \
+		const struct uts_namespace *:    &(__ns)->ns)
 
 #define ns_init_inum(__ns)                                     \
 	_Generic((__ns),                                       \
@@ -85,4 +93,21 @@ void __ns_common_free(struct ns_common *ns);
 
 #define ns_common_free(__ns) __ns_common_free(to_ns_common((__ns)))
 
+static __always_inline __must_check bool __ns_ref_put(struct ns_common *ns)
+{
+	return refcount_dec_and_test(&ns->count);
+}
+
+static __always_inline __must_check bool __ns_ref_get(struct ns_common *ns)
+{
+	return refcount_inc_not_zero(&ns->count);
+}
+
+#define ns_ref_read(__ns) refcount_read(&to_ns_common((__ns))->count)
+#define ns_ref_inc(__ns) refcount_inc(&to_ns_common((__ns))->count)
+#define ns_ref_get(__ns) __ns_ref_get(to_ns_common((__ns)))
+#define ns_ref_put(__ns) __ns_ref_put(to_ns_common((__ns)))
+#define ns_ref_put_and_lock(__ns, __lock) \
+	refcount_dec_and_lock(&to_ns_common((__ns))->count, (__lock))
+
 #endif

-- 
2.47.3