[PATCH 12/17] ns: make all reference counts on initial namespace a nop

Christian Brauner
2025-11-10T15:09:43Z

They are always active so no need to needlessly cacheline ping-pong.

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
include/linux/ns_common.h | 25 ++++++++++++++++++++++---
1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h
index b9e8f21a6984..5b8f2f0163d7 100644
--- a/include/linux/ns_common.h
+++ b/include/linux/ns_common.h
@@ -62,6 +62,8 @@ static __always_inline __must_check int __ns_ref_active_read(const struct ns_com

static __always_inline __must_check bool __ns_ref_put(struct ns_common *ns)
{
+ if (is_ns_init_id(ns))
+ return false;
if (refcount_dec_and_test(&ns->__ns_ref)) {
VFS_WARN_ON_ONCE(__ns_ref_active_read(ns));
return true;
@@ -71,6 +73,8 @@ static __always_inline __must_check bool __ns_ref_put(struct ns_common *ns)

static __always_inline __must_check bool __ns_ref_get(struct ns_common *ns)
{
+ if (is_ns_init_id(ns))
+ return true;
if (refcount_inc_not_zero(&ns->__ns_ref))
return true;
VFS_WARN_ON_ONCE(__ns_ref_active_read(ns));
@@ -82,12 +86,27 @@ static __always_inline __must_check int __ns_ref_read(const struct ns_common *ns
return refcount_read(&ns->__ns_ref);
}

+static __always_inline void __ns_ref_inc(struct ns_common *ns)
+{
+ if (is_ns_init_id(ns))
+ return;
+ refcount_inc(&ns->__ns_ref);
+}
+
+static __always_inline __must_check bool __ns_ref_dec_and_lock(struct ns_common *ns,
+ spinlock_t *ns_lock)
+{
+ if (is_ns_init_id(ns))
+ return false;
+ return refcount_dec_and_lock(&ns->__ns_ref, ns_lock);
+}
+
#define ns_ref_read(__ns) __ns_ref_read(to_ns_common((__ns)))
-#define ns_ref_inc(__ns) refcount_inc(&to_ns_common((__ns))->__ns_ref)
+#define ns_ref_inc(__ns) __ns_ref_inc(to_ns_common((__ns)))
#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))->__ns_ref, (__lock))
+#define ns_ref_put_and_lock(__ns, __ns_lock) \
+ __ns_ref_dec_and_lock(to_ns_common((__ns)), __ns_lock)

#define ns_ref_active_read(__ns) \
((__ns) ? __ns_ref_active_read(to_ns_common(__ns)) : 0)

--
2.47.3