The patch titled
ftrace: disable function tracing bringing up new CPU
has been added to the -mm tree. Its filename is
ftrace-disable-function-tracing-bringing-up-new-cpu.patch
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------------------------------------------------------
Subject: ftrace: disable function tracing bringing up new CPU
From: Steven Rostedt <rostedt@xxxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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(-)
diff -puN include/linux/ftrace.h~ftrace-disable-function-tracing-bringing-up-new-cpu include/linux/ftrace.h
--- a/include/linux/ftrace.h~ftrace-disable-function-tracing-bringing-up-new-cpu
+++ a/include/linux/ftrace.h
@@ -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
diff -puN kernel/cpu.c~ftrace-disable-function-tracing-bringing-up-new-cpu kernel/cpu.c
--- a/kernel/cpu.c~ftrace-disable-function-tracing-bringing-up-new-cpu
+++ a/kernel/cpu.c
@@ -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);
@@ -294,8 +295,16 @@ 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));
diff -puN kernel/trace/ftrace.c~ftrace-disable-function-tracing-bringing-up-new-cpu kernel/trace/ftrace.c
--- a/kernel/trace/ftrace.c~ftrace-disable-function-tracing-bringing-up-new-cpu
+++ a/kernel/trace/ftrace.c
@@ -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;
diff -puN kernel/trace/trace_irqsoff.c~ftrace-disable-function-tracing-bringing-up-new-cpu kernel/trace/trace_irqsoff.c
--- a/kernel/trace/trace_irqsoff.c~ftrace-disable-function-tracing-bringing-up-new-cpu
+++ a/kernel/trace/trace_irqsoff.c
@@ -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.
diff -puN kernel/trace/trace_sched_wakeup.c~ftrace-disable-function-tracing-bringing-up-new-cpu kernel/trace/trace_sched_wakeup.c
--- a/kernel/trace/trace_sched_wakeup.c~ftrace-disable-function-tracing-bringing-up-new-cpu
+++ a/kernel/trace/trace_sched_wakeup.c
@@ -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();
_
Patches currently in -mm which might be from rostedt@xxxxxxxxxxx are
linux-next.patch
ftrace-disable-function-tracing-bringing-up-new-cpu.patch
split-the-typecheck-macros-out-of-include-linux-kernelh.patch
locking-add-typecheck-on-irqsave-and-friends-for-correct-flags.patch
locking-add-typecheck-on-irqsave-and-friends-for-correct-flags-fix.patch
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