kernel: pid_namespace: simplify sysctls with register_sysctl()

register_sysctl_paths() is only required if your child (directories)
have entries and pid_namespace does not. So use register_sysctl_init()
instead where we don't care about the return value and use
register_sysctl() where we do.
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Acked-by: Jeff Xu <jeffxu@google.com>
Link: https://lore.kernel.org/r/20230302202826.776286-9-mcgrof@kernel.org

kernel/pid_namespace.c

@@ -314,7 +314,6 @@ static struct ctl_table pid_ns_ctl_table[] = {
 	},
 	{ }
 };
-static struct ctl_path kern_path[] = { { .procname = "kernel", }, { } };
 #endif	/* CONFIG_CHECKPOINT_RESTORE */
 
 int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd)
@@ -473,7 +472,7 @@ static __init int pid_namespaces_init(void)
 	pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC | SLAB_ACCOUNT);
 
 #ifdef CONFIG_CHECKPOINT_RESTORE
-	register_sysctl_paths(kern_path, pid_ns_ctl_table);
+	register_sysctl_init("kernel", pid_ns_ctl_table);
 #endif
 
 	register_pid_ns_sysctl_table_vm();

kernel/pid_sysctl.h

@@ -46,10 +46,9 @@ static struct ctl_table pid_ns_ctl_table_vm[] = {
 	},
 	{ }
 };
-static struct ctl_path vm_path[] = { { .procname = "vm", }, { } };
 static inline void register_pid_ns_sysctl_table_vm(void)
 {
-	register_sysctl_paths(vm_path, pid_ns_ctl_table_vm);
+	register_sysctl("vm", pid_ns_ctl_table_vm);
 }
 #else
 static inline void initialize_memfd_noexec_scope(struct pid_namespace *ns) {}