linux-kernel - [PATCH] tracing: branch tracer, fix vdso crash

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Date:	Wed, 12 Nov 2008 13:27:15 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Theodore Tso <tytso@....edu>,
	Arjan van de Ven <arjan@...radead.org>,
	Steven Rostedt <srostedt@...hat.com>
Subject: [PATCH] tracing: branch tracer, fix vdso crash

>From 2b7d0390a6d6d595f43ea3806639664afe5b9ebe Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@...e.hu>
Date: Wed, 12 Nov 2008 13:17:38 +0100
Subject: [PATCH] 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: Ingo Molnar <mingo@...e.hu>
---
 arch/x86/kernel/vsyscall_64.c  |    9 ++-------
 arch/x86/vdso/vclock_gettime.c |    3 +++
 include/linux/compiler.h       |    6 +++++-
 3 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index 2f90202..ece0293 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/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>
diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index 1ef0f90..6e66763 100644
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/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>
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 935e30c..63b7d90 100644
--- a/include/linux/compiler.h
+++ b/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;
--
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