tracing: branch tracer, fix vdso crash

Impact: fix bootup crash

the branch tracer missed arch/x86/vdso/vclock_gettime.c from
disabling tracing, which caused such bootup crashes:

  [  201.840097] init[1]: segfault at 7fffed3fe7c0 ip 00007fffed3fea2e sp 000077

also clean up the ugly ifdefs in arch/x86/kernel/vsyscall_64.c by
creating DISABLE_UNLIKELY_PROFILE facility for code to turn off
instrumentation on a per file basis.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/vsyscall_64.c

@@ -17,13 +17,8 @@
  *  want per guest time just set the kernel.vsyscall64 sysctl to 0.
  */
 
-/* Protect userspace from profiling */
-#ifdef CONFIG_TRACE_UNLIKELY_PROFILE
-# undef likely
-# undef unlikely
-# define likely(x)		likely_notrace(x)
-# define unlikely(x)		unlikely_notrace(x)
-#endif
+/* Disable profiling for userspace code: */
+#define DISABLE_UNLIKELY_PROFILE
 
 #include <linux/time.h>
 #include <linux/init.h>

arch/x86/vdso/vclock_gettime.c

@@ -9,6 +9,9 @@
  * Also alternative() doesn't work.
  */
 
+/* Disable profiling for userspace code: */
+#define DISABLE_UNLIKELY_PROFILE
+
 #include <linux/kernel.h>
 #include <linux/posix-timers.h>
 #include <linux/time.h>

include/linux/compiler.h

@@ -59,7 +59,11 @@ extern void __chk_io_ptr(const volatile void __iomem *);
  * specific implementations come from the above header files
  */
 
-#ifdef CONFIG_TRACE_UNLIKELY_PROFILE
+/*
+ * Note: DISABLE_UNLIKELY_PROFILE can be used by special lowlevel code
+ * to disable branch tracing on a per file basis.
+ */
+#if defined(CONFIG_TRACE_UNLIKELY_PROFILE) && !defined(DISABLE_UNLIKELY_PROFILE)
 struct ftrace_likely_data {
 	const char *func;
 	const char *file;