lib/alloc_tag: do not register sysctl interface when CONFIG_SYSCTL=n

Memory allocation profiling is trying to register sysctl interface even
when CONFIG_SYSCTL=n, resulting in proc_do_static_key() being undefined. 
Prevent that by skipping sysctl registration for such configurations.

Link: https://lkml.kernel.org/r/20240601233831.617124-1-surenb@google.com
Fixes: 22d407b1 ("lib: add allocation tagging support for memory allocation profiling")
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202405280616.wcOGWJEj-lkp@intel.com/Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Kees Cook <keescook@chromium.org>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/alloc_tag.c

@@ -227,6 +227,7 @@ struct page_ext_operations page_alloc_tagging_ops = {
 };
 EXPORT_SYMBOL(page_alloc_tagging_ops);
 
+#ifdef CONFIG_SYSCTL
 static struct ctl_table memory_allocation_profiling_sysctls[] = {
 	{
 		.procname	= "mem_profiling",
@@ -241,6 +242,17 @@ static struct ctl_table memory_allocation_profiling_sysctls[] = {
 	{ }
 };
 
+static void __init sysctl_init(void)
+{
+	if (!mem_profiling_support)
+		memory_allocation_profiling_sysctls[0].mode = 0444;
+
+	register_sysctl_init("vm", memory_allocation_profiling_sysctls);
+}
+#else /* CONFIG_SYSCTL */
+static inline void sysctl_init(void) {}
+#endif /* CONFIG_SYSCTL */
+
 static int __init alloc_tag_init(void)
 {
 	const struct codetag_type_desc desc = {
@@ -253,9 +265,7 @@ static int __init alloc_tag_init(void)
 	if (IS_ERR(alloc_tag_cttype))
 		return PTR_ERR(alloc_tag_cttype);
 
-	if (!mem_profiling_support)
-		memory_allocation_profiling_sysctls[0].mode = 0444;
-	register_sysctl_init("vm", memory_allocation_profiling_sysctls);
+	sysctl_init();
 	procfs_init();
 
 	return 0;