Support the generic namespace iterator and lookup infrastructure to
support file handles for namespaces.

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 include/linux/time_namespace.h |  5 +++++
 init/main.c                    |  2 ++
 kernel/time/namespace.c        | 13 +++++++++++--
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/include/linux/time_namespace.h b/include/linux/time_namespace.h
index bb2c52f4fc94..7f6af7a9771e 100644
--- a/include/linux/time_namespace.h
+++ b/include/linux/time_namespace.h
@@ -33,6 +33,7 @@ struct time_namespace {
 extern struct time_namespace init_time_ns;
 
 #ifdef CONFIG_TIME_NS
+void __init time_ns_init(void);
 extern int vdso_join_timens(struct task_struct *task,
 			    struct time_namespace *ns);
 extern void timens_commit(struct task_struct *tsk, struct time_namespace *ns);
@@ -108,6 +109,10 @@ static inline ktime_t timens_ktime_to_host(clockid_t clockid, ktime_t tim)
 }
 
 #else
+static inline void __init time_ns_init(void)
+{
+}
+
 static inline int vdso_join_timens(struct task_struct *task,
 				   struct time_namespace *ns)
 {
diff --git a/init/main.c b/init/main.c
index 0ee0ee7b7c2c..e7d2c57c65a7 100644
--- a/init/main.c
+++ b/init/main.c
@@ -103,6 +103,7 @@
 #include <linux/randomize_kstack.h>
 #include <linux/pidfs.h>
 #include <linux/ptdump.h>
+#include <linux/time_namespace.h>
 #include <net/net_namespace.h>
 
 #include <asm/io.h>
@@ -1072,6 +1073,7 @@ void start_kernel(void)
 	fork_init();
 	proc_caches_init();
 	uts_ns_init();
+	time_ns_init();
 	key_init();
 	security_init();
 	dbg_late_init();
diff --git a/kernel/time/namespace.c b/kernel/time/namespace.c
index 80b3d2ce2fb6..408f60d0a3b6 100644
--- a/kernel/time/namespace.c
+++ b/kernel/time/namespace.c
@@ -12,6 +12,7 @@
 #include <linux/seq_file.h>
 #include <linux/proc_ns.h>
 #include <linux/export.h>
+#include <linux/nstree.h>
 #include <linux/time.h>
 #include <linux/slab.h>
 #include <linux/cred.h>
@@ -88,7 +89,7 @@ static struct time_namespace *clone_time_ns(struct user_namespace *user_ns,
 		goto fail;
 
 	err = -ENOMEM;
-	ns = kmalloc(sizeof(*ns), GFP_KERNEL_ACCOUNT);
+	ns = kzalloc(sizeof(*ns), GFP_KERNEL_ACCOUNT);
 	if (!ns)
 		goto fail_dec;
 
@@ -104,6 +105,7 @@ static struct time_namespace *clone_time_ns(struct user_namespace *user_ns,
 	ns->user_ns = get_user_ns(user_ns);
 	ns->offsets = old_ns->offsets;
 	ns->frozen_offsets = false;
+	ns_tree_add(ns);
 	return ns;
 
 fail_free_page:
@@ -250,11 +252,13 @@ static void timens_set_vvar_page(struct task_struct *task,
 
 void free_time_ns(struct time_namespace *ns)
 {
+	ns_tree_remove(ns);
 	dec_time_namespaces(ns->ucounts);
 	put_user_ns(ns->user_ns);
 	ns_free_inum(&ns->ns);
 	__free_page(ns->vvar_page);
-	kfree(ns);
+	/* Concurrent nstree traversal depends on a grace period. */
+	kfree_rcu(ns, ns.ns_rcu);
 }
 
 static struct time_namespace *to_time_ns(struct ns_common *ns)
@@ -487,3 +491,8 @@ struct time_namespace init_time_ns = {
 	.ns.ops		= &timens_operations,
 	.frozen_offsets	= true,
 };
+
+void __init time_ns_init(void)
+{
+	ns_tree_add(&init_time_ns);
+}

-- 
2.47.3

On Wed, Sep 10 2025 at 16:37, Christian Brauner wrote:
> Support the generic namespace iterator and lookup infrastructure to
> support file handles for namespaces.
>
> Signed-off-by: Christian Brauner <brauner@kernel.org>

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>