linux-kernel - Re: ftrace and kexec

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Date:	Tue, 19 Feb 2008 15:22:39 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Dhaval Giani <dhaval@...ux.vnet.ibm.com>
Cc:	vgoyal@...hat.com, rostedt@...dmis.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: ftrace and kexec


* Dhaval Giani <dhaval@...ux.vnet.ibm.com> wrote:

> Hi,
> 
> I've been running ftrace on the sched-devel tree. I just built a 
> kernel and tried rebooting using kexec and I get this,

hm, it's not a good idea to keep using the data structures of the tracer 
while we kexec. Does the patch below resolve the problem?

	Ingo

-------------------------->
Subject: x86: patches/ftrace-kexec-fix.patch
From: Ingo Molnar <mingo@...e.hu>
Date: Tue Feb 19 15:13:56 CET 2008

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 arch/x86/kernel/machine_kexec_32.c |    4 ++++
 arch/x86/kernel/machine_kexec_64.c |    4 ++++
 include/linux/ftrace.h             |    7 +++++++
 3 files changed, 15 insertions(+)

Index: linux/arch/x86/kernel/machine_kexec_32.c
===================================================================
--- linux.orig/arch/x86/kernel/machine_kexec_32.c
+++ linux/arch/x86/kernel/machine_kexec_32.c
@@ -11,6 +11,8 @@
 #include <linux/delay.h>
 #include <linux/init.h>
 #include <linux/numa.h>
+#include <linux/ftrace.h>
+
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
 #include <asm/tlbflush.h>
@@ -107,6 +109,8 @@ NORET_TYPE void machine_kexec(struct kim
 	unsigned long page_list[PAGES_NR];
 	void *control_page;
 
+	tracer_disable();
+
 	/* Interrupts aren't acceptable while we reboot */
 	local_irq_disable();
 
Index: linux/arch/x86/kernel/machine_kexec_64.c
===================================================================
--- linux.orig/arch/x86/kernel/machine_kexec_64.c
+++ linux/arch/x86/kernel/machine_kexec_64.c
@@ -11,6 +11,8 @@
 #include <linux/string.h>
 #include <linux/reboot.h>
 #include <linux/numa.h>
+#include <linux/ftrace.h>
+
 #include <asm/pgtable.h>
 #include <asm/tlbflush.h>
 #include <asm/mmu_context.h>
@@ -184,6 +186,8 @@ NORET_TYPE void machine_kexec(struct kim
 	unsigned long page_list[PAGES_NR];
 	void *control_page;
 
+	tracer_disable();
+
 	/* Interrupts aren't acceptable while we reboot */
 	local_irq_disable();
 
Index: linux/include/linux/ftrace.h
===================================================================
--- linux.orig/include/linux/ftrace.h
+++ linux/include/linux/ftrace.h
@@ -68,6 +68,13 @@ extern void ftrace_call(void);
 extern void mcount_call(void);
 #endif
 
+static inline void tracer_disable(void)
+{
+#ifdef CONFIG_FTRACE
+	ftrace_enabled = 0;
+#endif
+}
+
 #ifdef CONFIG_FRAME_POINTER
 /* TODO: need to fix this for ARM */
 # define CALLER_ADDR0 ((unsigned long)__builtin_return_address(0))
--
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