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

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 kernel/cgroup/cgroup.c    | 2 ++
 kernel/cgroup/namespace.c | 7 +++++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 312c6a8b55bb..092e6bf081ed 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -59,6 +59,7 @@
 #include <linux/sched/cputime.h>
 #include <linux/sched/deadline.h>
 #include <linux/psi.h>
+#include <linux/nstree.h>
 #include <net/sock.h>
 
 #define CREATE_TRACE_POINTS
@@ -6312,6 +6313,7 @@ int __init cgroup_init(void)
 	WARN_ON(register_filesystem(&cpuset_fs_type));
 #endif
 
+	ns_tree_add(&init_cgroup_ns);
 	return 0;
 }
 
diff --git a/kernel/cgroup/namespace.c b/kernel/cgroup/namespace.c
index 0391b6ab0bf1..fc12c416dfeb 100644
--- a/kernel/cgroup/namespace.c
+++ b/kernel/cgroup/namespace.c
@@ -5,7 +5,7 @@
 #include <linux/slab.h>
 #include <linux/nsproxy.h>
 #include <linux/proc_ns.h>
-
+#include <linux/nstree.h>
 
 /* cgroup namespaces */
 
@@ -30,16 +30,19 @@ static struct cgroup_namespace *alloc_cgroup_ns(void)
 	ret = ns_common_init(&new_ns->ns, &cgroupns_operations, true);
 	if (ret)
 		return ERR_PTR(ret);
+	ns_tree_add(new_ns);
 	return no_free_ptr(new_ns);
 }
 
 void free_cgroup_ns(struct cgroup_namespace *ns)
 {
+	ns_tree_remove(ns);
 	put_css_set(ns->root_cset);
 	dec_cgroup_namespaces(ns->ucounts);
 	put_user_ns(ns->user_ns);
 	ns_free_inum(&ns->ns);
-	kfree(ns);
+	/* Concurrent nstree traversal depends on a grace period. */
+	kfree_rcu(ns, ns.ns_rcu);
 }
 EXPORT_SYMBOL(free_cgroup_ns);
 

-- 
2.47.3

On Wed, Sep 10, 2025 at 04:37:03PM +0200, Christian Brauner wrote:
> Support the generic namespace iterator and lookup infrastructure to
> support file handles for namespaces.

The patch subject seems a bit too generic and could be misleading. Maybe it
should mention it's for namespaces? Other than that,

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun