compiler_types.h, kasan: Use __SANITIZE_ADDRESS__ instead of CONFIG_KASAN to decide inlining

Use __always_inline in compilation units that have instrumentation
disabled (KASAN_SANITIZE_foo.o := n) for KASAN, like it is done for
KCSAN.

Also, add common documentation for KASAN and KCSAN explaining the
attribute.

 [ bp: Massage commit message. ]

Signed-off-by: Marco Elver <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Will Deacon <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

Author: melver

include/linux/compiler_types.h

@@ -171,7 +171,14 @@ struct ftrace_likely_data {
  */
 #define noinline_for_stack noinline
 
-#ifdef CONFIG_KASAN
+/*
+ * Sanitizer helper attributes: Because using __always_inline and
+ * __no_sanitize_* conflict, provide helper attributes that will either expand
+ * to __no_sanitize_* in compilation units where instrumentation is enabled
+ * (__SANITIZE_*__), or __always_inline in compilation units without
+ * instrumentation (__SANITIZE_*__ undefined).
+ */
+#ifdef __SANITIZE_ADDRESS__
 /*
  * We can't declare function 'inline' because __no_sanitize_address conflicts
  * with inlining. Attempt to inline it may cause a build failure.
@@ -186,10 +193,6 @@ struct ftrace_likely_data {
 
 #define __no_kcsan __no_sanitize_thread
 #ifdef __SANITIZE_THREAD__
-/*
- * Rely on __SANITIZE_THREAD__ instead of CONFIG_KCSAN, to avoid not inlining in
- * compilation units where instrumentation is disabled.
- */
 # define __no_kcsan_or_inline __no_kcsan notrace __maybe_unused
 # define __no_sanitize_or_inline __no_kcsan_or_inline
 #else