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

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Message-Id: <20251110-work-namespace-nstree-fixes-v1-13-e8a9264e0fb9@kernel.org>
Date: Mon, 10 Nov 2025 16:08:25 +0100
From: Christian Brauner <brauner@...nel.org>
To: linux-fsdevel@...r.kernel.org, Josef Bacik <josef@...icpanda.com>, 
 Jeff Layton <jlayton@...nel.org>
Cc: Jann Horn <jannh@...gle.com>, Mike Yuan <me@...dnzj.com>, 
 Zbigniew Jędrzejewski-Szmek <zbyszek@...waw.pl>, 
 Lennart Poettering <mzxreary@...inter.de>, 
 Daan De Meyer <daan.j.demeyer@...il.com>, Aleksa Sarai <cyphar@...har.com>, 
 Amir Goldstein <amir73il@...il.com>, Tejun Heo <tj@...nel.org>, 
 Johannes Weiner <hannes@...xchg.org>, Thomas Gleixner <tglx@...utronix.de>, 
 Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, 
 linux-kernel@...r.kernel.org, cgroups@...r.kernel.org, bpf@...r.kernel.org, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 netdev@...r.kernel.org, Arnd Bergmann <arnd@...db.de>, 
 Christian Brauner <brauner@...nel.org>
Subject: [PATCH 13/17] ns: add asserts for initial namespace reference
 counts

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

Signed-off-by: Christian Brauner <brauner@...nel.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