[PATCH] ftrace: disable function tracing bringing up new CPU

* [PATCH] ftrace: disable function tracing bringing up new CPU
@ 2008-06-05 20:54 Steven Rostedt
  2008-06-05 23:19 ` [PATCH -v2] " Steven Rostedt
  0 siblings, 1 reply; 3+ messages in thread
From: Steven Rostedt @ 2008-06-05 20:54 UTC (permalink / raw)
  To: Ingo Molnar; +Cc: LKML, Thomas Gleixner, Peter Zijlstra, Rusty Russell, akpm


Peter Zijlstra found that taking down and bringing up a new CPU caused
ftrace to crash the kernel. This was due to some arch calls that were
being traced by the function tracer before the smp_processor_id was set
up. Since the function tracer uses smp_processor_id it caused a triple
fault.

Instead of adding notrace all over the architecture code to prevent
this problem, it is easier to simply disable the function tracer
when bringing up a new CPU.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
---
 include/linux/ftrace.h            |   11 ++++++++---
 kernel/cpu.c                      |    9 +++++++++
 kernel/trace/ftrace.c             |   28 ++++++++++++++++++++++++++++
 kernel/trace/trace_irqsoff.c      |    3 +++
 kernel/trace/trace_sched_wakeup.c |    2 +-
 5 files changed, 49 insertions(+), 4 deletions(-)

Index: linux-tip.git/include/linux/ftrace.h
===================================================================

--- linux-tip.git.orig/include/linux/ftrace.h	2008-06-05 14:51:47.000000000 -0400
+++ linux-tip.git/include/linux/ftrace.h	2008-06-05 16:52:32.000000000 -0400
@@ -33,10 +33,15 @@ void clear_ftrace_function(void);
 extern void ftrace_stub(unsigned long a0, unsigned long a1);
 extern void mcount(void);

+void ftrace_enable(void);
+void ftrace_disable(void);
+
 #else /* !CONFIG_FTRACE */
-# define register_ftrace_function(ops) do { } while (0)
-# define unregister_ftrace_function(ops) do { } while (0)
-# define clear_ftrace_function(ops) do { } while (0)
+# define register_ftrace_function(ops)		do { } while (0)
+# define unregister_ftrace_function(ops)	do { } while (0)
+# define clear_ftrace_function(ops)		do { } while (0)
+# define ftrace_enable()			do { } while (0)
+# define ftrace_disable()			do { } while (0)
 #endif /* CONFIG_FTRACE */

 #ifdef CONFIG_DYNAMIC_FTRACE
Index: linux-tip.git/kernel/cpu.c
===================================================================
--- linux-tip.git.orig/kernel/cpu.c	2008-06-05 14:50:44.000000000 -0400
+++ linux-tip.git/kernel/cpu.c	2008-06-05 14:51:50.000000000 -0400
@@ -14,6 +14,7 @@
 #include <linux/kthread.h>
 #include <linux/stop_machine.h>
 #include <linux/mutex.h>
+#include <linux/ftrace.h>

 /* Serializes the updates to cpu_online_map, cpu_present_map */
 static DEFINE_MUTEX(cpu_add_remove_lock);
@@ -300,8 +301,16 @@ static int __cpuinit _cpu_up(unsigned in
 		goto out_notify;
 	}

+	/*
+	 * Disable function tracing while bringing up a new CPU.
+	 * We don't want to trace functions that can not handle a
+	 * smp_processor_id() call.
+	 */
+	ftrace_disable();
+
 	/* Arch-specific enabling code. */
 	ret = __cpu_up(cpu);
+	ftrace_enable();
 	if (ret != 0)
 		goto out_notify;
 	BUG_ON(!cpu_online(cpu));
Index: linux-tip.git/kernel/trace/ftrace.c
===================================================================
--- linux-tip.git.orig/kernel/trace/ftrace.c	2008-06-05 14:50:44.000000000 -0400
+++ linux-tip.git/kernel/trace/ftrace.c	2008-06-05 16:41:09.000000000 -0400
@@ -148,6 +148,34 @@ static int __unregister_ftrace_function(
 	return ret;
 }

+static int ftrace_disabled_count;
+static int save_ftrace_enabled;
+
+void ftrace_disable(void)
+{
+	unsigned long flags;
+
+	mutex_lock(&ftrace_sysctl_lock);
+
+	save_ftrace_enabled = ftrace_enabled;
+	ftrace_enabled = 0;
+}
+
+void ftrace_enable(void)
+{
+	unsigned long flags;
+
+	/* ftrace_enable must be paired with ftrace_disable */
+	if (!mutex_is_locked(&ftrace_sysctl_lock)) {
+		WARN_ON(1);
+		return;
+	}
+
+	ftrace_enabled = save_ftrace_enabled;
+
+	mutex_unlock(&ftrace_sysctl_lock);
+}
+
 #ifdef CONFIG_DYNAMIC_FTRACE

 static struct task_struct *ftraced_task;
Index: linux-tip.git/kernel/trace/trace_irqsoff.c
===================================================================
--- linux-tip.git.orig/kernel/trace/trace_irqsoff.c	2008-06-05 14:50:44.000000000 -0400
+++ linux-tip.git/kernel/trace/trace_irqsoff.c	2008-06-05 14:51:50.000000000 -0400
@@ -76,6 +76,9 @@ irqsoff_tracer_call(unsigned long ip, un
 	long disabled;
 	int cpu;

+	if (unlikely(!ftrace_enabled))
+		return;
+
 	/*
 	 * Does not matter if we preempt. We test the flags
 	 * afterward, to see if irqs are disabled or not.
Index: linux-tip.git/kernel/trace/trace_sched_wakeup.c
===================================================================
--- linux-tip.git.orig/kernel/trace/trace_sched_wakeup.c	2008-06-05 14:50:44.000000000 -0400
+++ linux-tip.git/kernel/trace/trace_sched_wakeup.c	2008-06-05 14:51:50.000000000 -0400
@@ -44,7 +44,7 @@ wakeup_tracer_call(unsigned long ip, uns
 	int resched;
 	int cpu;

-	if (likely(!wakeup_task))
+	if (likely(!wakeup_task) || !ftrace_enabled)
 		return;

 	resched = need_resched();

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