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Date: Thu, 5 Jun 2008 19:19:08 -0400 (EDT)
From: Steven Rostedt <rostedt@...dmis.org>
To: Ingo Molnar <mingo@...e.hu>
cc: LKML <linux-kernel@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Rusty Russell <rusty@...tcorp.com.au>, akpm@...l.org
Subject: [PATCH -v2] ftrace: disable function tracing bringing up new CPU
[
I noticed that I left a "unsigned long flags" in the version I sent out.
That was due to my first faulty implementation that used a spin lock.
Please use this patch instead. The only difference between this patch
and the one I sent out is that I removed the unused flags variables
from ftrace_enable() and ftrace_disable().
]
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@...hat.com>
---
include/linux/ftrace.h | 11 ++++++++---
kernel/cpu.c | 9 +++++++++
kernel/trace/ftrace.c | 24 ++++++++++++++++++++++++
kernel/trace/trace_irqsoff.c | 3 +++
kernel/trace/trace_sched_wakeup.c | 2 +-
5 files changed, 45 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 18:17:14.000000000 -0400
@@ -148,6 +148,30 @@ static int __unregister_ftrace_function(
return ret;
}
+static int ftrace_disabled_count;
+static int save_ftrace_enabled;
+
+void ftrace_disable(void)
+{
+ mutex_lock(&ftrace_sysctl_lock);
+
+ save_ftrace_enabled = ftrace_enabled;
+ ftrace_enabled = 0;
+}
+
+void ftrace_enable(void)
+{
+ /* 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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