Merge patch series "ns: rework reference counting"

Christian Brauner <brauner@kernel.org> says:

Stop open accesses to the reference counts and cargo-culting the same
code in all namespace. Use a set of dedicated helpers and make the
actual count private.

* patches from https://lore.kernel.org/20250918-work-namespace-ns_ref-v1-0-1b0a98ee041e@kernel.org:
  ns: rename to __ns_ref
  nsfs: port to ns_ref_*() helpers
  net: port to ns_ref_*() helpers
  uts: port to ns_ref_*() helpers
  ipv4: use check_net()
  net: use check_net()
  net-sysfs: use check_net()
  user: port to ns_ref_*() helpers
  time: port to ns_ref_*() helpers
  pid: port to ns_ref_*() helpers
  ipc: port to ns_ref_*() helpers
  cgroup: port to ns_ref_*() helpers
  mnt: port to ns_ref_*() helpers
  ns: add reference count helpers

Signed-off-by: Christian Brauner <brauner@kernel.org>

7 files changed, 47 insertions, 22 deletions

diff --git a/include/linux/cgroup_namespace.h b/include/linux/cgroup_namespace.h
index c02bb76c5e32..b7dbf4d623d2 100644
--- a/include/linux/cgroup_namespace.h
+++ b/include/linux/cgroup_namespace.h
@@ -29,12 +29,12 @@ int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
 
 static inline void get_cgroup_ns(struct cgroup_namespace *ns)
 {
-	refcount_inc(&ns->ns.count);
+	ns_ref_inc(ns);
 }
 
 static inline void put_cgroup_ns(struct cgroup_namespace *ns)
 {
-	if (refcount_dec_and_test(&ns->ns.count))
+	if (ns_ref_put(ns))
 		free_cgroup_ns(ns);
 }
 
diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h
index 924e4754374f..21eff63f47da 100644
--- a/include/linux/ipc_namespace.h
+++ b/include/linux/ipc_namespace.h
@@ -140,14 +140,14 @@ extern struct ipc_namespace *copy_ipcs(unsigned long flags,
 static inline struct ipc_namespace *get_ipc_ns(struct ipc_namespace *ns)
 {
 	if (ns)
-		refcount_inc(&ns->ns.count);
+		ns_ref_inc(ns);
 	return ns;
 }
 
 static inline struct ipc_namespace *get_ipc_ns_not_zero(struct ipc_namespace *ns)
 {
 	if (ns) {
-		if (refcount_inc_not_zero(&ns->ns.count))
+		if (ns_ref_get(ns))
 			return ns;
 	}
 
diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h
index 19833ac547f9..aea8528d799a 100644
--- a/include/linux/ns_common.h
+++ b/include/linux/ns_common.h
@@ -29,7 +29,7 @@ struct ns_common {
 	struct dentry *stashed;
 	const struct proc_ns_operations *ops;
 	unsigned int inum;
-	refcount_t count;
+	refcount_t __ns_ref; /* do not use directly */
 	union {
 		struct {
 			u64 ns_id;
@@ -43,16 +43,24 @@ struct ns_common {
 int __ns_common_init(struct ns_common *ns, const struct proc_ns_operations *ops, int inum);
 void __ns_common_free(struct ns_common *ns);
 
-#define to_ns_common(__ns)                              \
-	_Generic((__ns),                                \
-		struct cgroup_namespace *: &(__ns)->ns, \
-		struct ipc_namespace *:    &(__ns)->ns, \
-		struct mnt_namespace *:    &(__ns)->ns, \
-		struct net *:              &(__ns)->ns, \
-		struct pid_namespace *:    &(__ns)->ns, \
-		struct time_namespace *:   &(__ns)->ns, \
-		struct user_namespace *:   &(__ns)->ns, \
-		struct uts_namespace *:    &(__ns)->ns)
+#define to_ns_common(__ns)                                    \
+	_Generic((__ns),                                      \
+		struct cgroup_namespace *:       &(__ns)->ns, \
+		const struct cgroup_namespace *: &(__ns)->ns, \
+		struct ipc_namespace *:          &(__ns)->ns, \
+		const struct ipc_namespace *:    &(__ns)->ns, \
+		struct mnt_namespace *:          &(__ns)->ns, \
+		const struct mnt_namespace *:    &(__ns)->ns, \
+		struct net *:                    &(__ns)->ns, \
+		const struct net *:              &(__ns)->ns, \
+		struct pid_namespace *:          &(__ns)->ns, \
+		const struct pid_namespace *:    &(__ns)->ns, \
+		struct time_namespace *:         &(__ns)->ns, \
+		const struct time_namespace *:   &(__ns)->ns, \
+		struct user_namespace *:         &(__ns)->ns, \
+		const struct user_namespace *:   &(__ns)->ns, \
+		struct uts_namespace *:          &(__ns)->ns, \
+		const struct uts_namespace *:    &(__ns)->ns)
 
 #define ns_init_inum(__ns)                                     \
 	_Generic((__ns),                                       \
@@ -83,4 +91,21 @@ void __ns_common_free(struct ns_common *ns);
 
 #define ns_common_free(__ns) __ns_common_free(to_ns_common((__ns)))
 
+static __always_inline __must_check bool __ns_ref_put(struct ns_common *ns)
+{
+	return refcount_dec_and_test(&ns->__ns_ref);
+}
+
+static __always_inline __must_check bool __ns_ref_get(struct ns_common *ns)
+{
+	return refcount_inc_not_zero(&ns->__ns_ref);
+}
+
+#define ns_ref_read(__ns) refcount_read(&to_ns_common((__ns))->__ns_ref)
+#define ns_ref_inc(__ns) refcount_inc(&to_ns_common((__ns))->__ns_ref)
+#define ns_ref_get(__ns) __ns_ref_get(to_ns_common((__ns)))
+#define ns_ref_put(__ns) __ns_ref_put(to_ns_common((__ns)))
+#define ns_ref_put_and_lock(__ns, __lock) \
+	refcount_dec_and_lock(&to_ns_common((__ns))->__ns_ref, (__lock))
+
 #endif
diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index ba0efc8c8596..5b2f29d369c4 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -62,7 +62,7 @@ static inline struct pid_namespace *to_pid_ns(struct ns_common *ns)
 static inline struct pid_namespace *get_pid_ns(struct pid_namespace *ns)
 {
 	if (ns != &init_pid_ns)
-		refcount_inc(&ns->ns.count);
+		ns_ref_inc(ns);
 	return ns;
 }
 
diff --git a/include/linux/time_namespace.h b/include/linux/time_namespace.h
index a47a4ce4183e..f3b9567cf1f4 100644
--- a/include/linux/time_namespace.h
+++ b/include/linux/time_namespace.h
@@ -44,7 +44,7 @@ extern void timens_commit(struct task_struct *tsk, struct time_namespace *ns);
 
 static inline struct time_namespace *get_time_ns(struct time_namespace *ns)
 {
-	refcount_inc(&ns->ns.count);
+	ns_ref_inc(ns);
 	return ns;
 }
 
@@ -57,7 +57,7 @@ struct page *find_timens_vvar_page(struct vm_area_struct *vma);
 
 static inline void put_time_ns(struct time_namespace *ns)
 {
-	if (refcount_dec_and_test(&ns->ns.count))
+	if (ns_ref_put(ns))
 		free_time_ns(ns);
 }
 
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index a09056ad090e..9a9aebbf96b9 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -176,7 +176,7 @@ static inline struct user_namespace *to_user_ns(struct ns_common *ns)
 static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
 {
 	if (ns)
-		refcount_inc(&ns->ns.count);
+		ns_ref_inc(ns);
 	return ns;
 }
 
@@ -186,7 +186,7 @@ extern void __put_user_ns(struct user_namespace *ns);
 
 static inline void put_user_ns(struct user_namespace *ns)
 {
-	if (ns && refcount_dec_and_test(&ns->ns.count))
+	if (ns && ns_ref_put(ns))
 		__put_user_ns(ns);
 }
 
diff --git a/include/linux/uts_namespace.h b/include/linux/uts_namespace.h
index c2b619bb4e57..23b4f0e1b338 100644
--- a/include/linux/uts_namespace.h
+++ b/include/linux/uts_namespace.h
@@ -25,7 +25,7 @@ static inline struct uts_namespace *to_uts_ns(struct ns_common *ns)
 
 static inline void get_uts_ns(struct uts_namespace *ns)
 {
-	refcount_inc(&ns->ns.count);
+	ns_ref_inc(ns);
 }
 
 extern struct uts_namespace *copy_utsname(unsigned long flags,
@@ -34,7 +34,7 @@ extern void free_uts_ns(struct uts_namespace *ns);
 
 static inline void put_uts_ns(struct uts_namespace *ns)
 {
-	if (refcount_dec_and_test(&ns->ns.count))
+	if (ns_ref_put(ns))
 		free_uts_ns(ns);
 }