[PATCH 13/17] ns: add asserts for initial namespace reference counts

Christian Brauner
2025-11-10T15:09:49Z

They always remain fixed at one. Notice when that assumptions is broken.

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
include/linux/ns_common.h | 26 +++++++++++++++++---------
1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h
index 5b8f2f0163d7..dfb6b798ba82 100644
--- a/include/linux/ns_common.h
+++ b/include/linux/ns_common.h
@@ -60,10 +60,17 @@ static __always_inline __must_check int __ns_ref_active_read(const struct ns_com
return atomic_read(&ns->__ns_ref_active);
}

+static __always_inline __must_check int __ns_ref_read(const struct ns_common *ns)
+{
+ return refcount_read(&ns->__ns_ref);
+}
+
static __always_inline __must_check bool __ns_ref_put(struct ns_common *ns)
{
- if (is_ns_init_id(ns))
+ if (is_ns_init_id(ns)) {
+ VFS_WARN_ON_ONCE(__ns_ref_read(ns) != 1);
return false;
+ }
if (refcount_dec_and_test(&ns->__ns_ref)) {
VFS_WARN_ON_ONCE(__ns_ref_active_read(ns));
return true;
@@ -73,31 +80,32 @@ 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))
+ if (is_ns_init_id(ns)) {
+ VFS_WARN_ON_ONCE(__ns_ref_read(ns) != 1);
return true;
+ }
if (refcount_inc_not_zero(&ns->__ns_ref))
return true;
VFS_WARN_ON_ONCE(__ns_ref_active_read(ns));
return false;
}

-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))
+ if (is_ns_init_id(ns)) {
+ VFS_WARN_ON_ONCE(__ns_ref_read(ns) != 1);
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))
+ if (is_ns_init_id(ns)) {
+ VFS_WARN_ON_ONCE(__ns_ref_read(ns) != 1);
return false;
+ }
return refcount_dec_and_lock(&ns->__ns_ref, ns_lock);
}

--
2.47.3