[PATCH 2/8] ns: don't increment or decrement initial namespaces
From: Christian Brauner <brauner@kernel.org>
Date: 2025-11-09 21:13:28
Also in:
bpf, cgroups, linux-fsdevel, lkml
Subsystem:
the rest · Maintainer:
Linus Torvalds
There's no need to bump the active reference counts of initial namespaces as they're always active and can simply remain at 1. Signed-off-by: Christian Brauner <brauner@kernel.org> --- include/linux/ns_common.h | 23 ++++++++++++++++++++--- kernel/nscommon.c | 6 ++++++ 2 files changed, 26 insertions(+), 3 deletions(-)
diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h
index bd4492ef6ffc..791b18dc77d0 100644
--- a/include/linux/ns_common.h
+++ b/include/linux/ns_common.h@@ -141,6 +141,12 @@ static __always_inline bool is_initial_namespace(struct ns_common *ns) IPC_NS_INIT_INO - MNT_NS_INIT_INO + 1)); } +static __always_inline bool is_ns_init_id(const struct ns_common *ns) +{ + VFS_WARN_ON_ONCE(ns->ns_id == 0); + return ns->ns_id <= NS_LAST_INIT_ID; +} + #define to_ns_common(__ns) \ _Generic((__ns), \ struct cgroup_namespace *: &(__ns)->ns, \
@@ -285,14 +291,19 @@ void __ns_ref_active_get_owner(struct ns_common *ns); static __always_inline void __ns_ref_active_get(struct ns_common *ns) { - WARN_ON_ONCE(atomic_add_negative(1, &ns->__ns_ref_active)); - VFS_WARN_ON_ONCE(is_initial_namespace(ns) && __ns_ref_active_read(ns) <= 0); + /* Initial namespaces are always active. */ + if (!is_ns_init_id(ns)) + WARN_ON_ONCE(atomic_add_negative(1, &ns->__ns_ref_active)); } #define ns_ref_active_get(__ns) \ do { if (__ns) __ns_ref_active_get(to_ns_common(__ns)); } while (0) static __always_inline bool __ns_ref_active_get_not_zero(struct ns_common *ns) { + /* Initial namespaces are always active. */ + if (is_ns_init_id(ns)) + return true; + if (atomic_inc_not_zero(&ns->__ns_ref_active)) { VFS_WARN_ON_ONCE(!__ns_ref_read(ns)); return true;
@@ -307,6 +318,10 @@ void __ns_ref_active_put_owner(struct ns_common *ns); static __always_inline void __ns_ref_active_put(struct ns_common *ns) { + /* Initial namespaces are always active. */ + if (is_ns_init_id(ns)) + return; + if (atomic_dec_and_test(&ns->__ns_ref_active)) { VFS_WARN_ON_ONCE(is_initial_namespace(ns)); VFS_WARN_ON_ONCE(!__ns_ref_read(ns));
@@ -319,8 +334,10 @@ static __always_inline void __ns_ref_active_put(struct ns_common *ns) static __always_inline struct ns_common *__must_check ns_get_unless_inactive(struct ns_common *ns) { VFS_WARN_ON_ONCE(__ns_ref_active_read(ns) && !__ns_ref_read(ns)); - if (!__ns_ref_active_read(ns)) + if (!__ns_ref_active_read(ns)) { + VFS_WARN_ON_ONCE(is_ns_init_id(ns)); return NULL; + } if (!__ns_ref_get(ns)) return NULL; return ns;
diff --git a/kernel/nscommon.c b/kernel/nscommon.c
index d67ae7ad7759..70cb66232e4c 100644
--- a/kernel/nscommon.c
+++ b/kernel/nscommon.c@@ -177,6 +177,7 @@ void __ns_ref_active_put_owner(struct ns_common *ns) ns = ns_owner(ns); if (!ns) return; + VFS_WARN_ON_ONCE(is_ns_init_id(ns)); if (!atomic_dec_and_test(&ns->__ns_ref_active)) return; }
@@ -276,6 +277,10 @@ void __ns_ref_active_put_owner(struct ns_common *ns) */ void __ns_ref_active_resurrect(struct ns_common *ns) { + /* Initial namespaces are always active. */ + if (is_ns_init_id(ns)) + return; + /* If we didn't resurrect the namespace we're done. */ if (atomic_fetch_add(1, &ns->__ns_ref_active)) return;
@@ -289,6 +294,7 @@ void __ns_ref_active_resurrect(struct ns_common *ns) if (!ns) return; + VFS_WARN_ON_ONCE(is_ns_init_id(ns)); if (atomic_fetch_add(1, &ns->__ns_ref_active)) return; }
--
2.47.3