sysctl: add register_sysctl() dummy helper

register_sysctl() has been around for five years with commit
fea478d4101a ("sysctl: Add register_sysctl for normal sysctl users") but
now that arm64 started using it, I ran into a compile error:

  arch/arm64/kernel/armv8_deprecated.c: In function 'register_insn_emulation_sysctl':
  arch/arm64/kernel/armv8_deprecated.c:257:2: error: implicit declaration of function 'register_sysctl'

This adds a inline function like we already have for
register_sysctl_paths() and register_sysctl_table().

Fixes: 38b9aeb32fa7 ("arm64: Port deprecated instruction emulation to new sysctl interface")
Signed-off-by: Arnd Bergmann <>
Reviewed-by: Dave Martin <>
Acked-by: Kees Cook <>
Acked-by: Will Deacon <>
Cc: Catalin Marinas <>
Cc: "Luis R. Rodriguez" <>
Cc: Alex Benne <>
Cc: Arnd Bergmann <>
Cc: "Eric W. Biederman" <>
Cc: Thomas Gleixner <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 74f91ee..b769ecf 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -213,6 +213,11 @@
 	return NULL;
+static inline struct ctl_table_header *register_sysctl(const char *path, struct ctl_table *table)
+	return NULL;
 static inline void unregister_sysctl_table(struct ctl_table_header * table)