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Date: Fri, 8 Aug 2008 10:30:06 -0400 (EDT)
From: Steven Rostedt <rostedt@...dmis.org>
To: Vivek Goyal <vgoyal@...hat.com>
cc: Huang Ying <ying.huang@...el.com>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Pavel Machek <pavel@....cz>, nigel@...el.suspend2.net,
"Rafael J. Wysocki" <rjw@...k.pl>,
Andrew Morton <akpm@...ux-foundation.org>, mingo@...e.hu,
Linus Torvalds <torvalds@...ux-foundation.org>,
linux-kernel@...r.kernel.org,
Kexec Mailing List <kexec@...ts.infradead.org>
Subject: Re: [PATCH -v2 7/8] kexec jump: ftrace_enabled_save/restore
On Fri, 8 Aug 2008, Vivek Goyal wrote:
> On Fri, Aug 08, 2008 at 02:52:48PM +0800, Huang Ying wrote:
> > Add ftrace_enabled_save/restore, used to disable ftrace for a
> > while. This is used by kexec jump.
> >
> > Signed-off-by: Huang Ying <ying.huang@...el.com>
> >
>
>
> CCing Steven Rostedt for ftrace related changes.
Thanks,
>
> > ---
> > include/linux/ftrace.h | 18 ++++++++++++++++++
> > 1 file changed, 18 insertions(+)
> >
> > --- a/include/linux/ftrace.h
> > +++ b/include/linux/ftrace.h
> > @@ -98,6 +98,24 @@ static inline void tracer_disable(void)
> > #endif
> > }
> >
> > +static inline int ftrace_enabled_save(void)
> > +{
> > +#ifdef CONFIG_FTRACE
> > + int saved_ftrace_enabled = ftrace_enabled;
> > + ftrace_enabled = 0;
> > + return saved_ftrace_enabled;
> > +#else
> > + return 0;
> > +#endif
> > +}
> > +
> > +static inline void ftrace_enabled_restore(int enabled)
> > +{
> > +#ifdef CONFIG_FTRACE
> > + ftrace_enabled = enabled;
> > +#endif
> > +}
> > +
> > #ifdef CONFIG_FRAME_POINTER
> > /* TODO: need to fix this for ARM */
> > # define CALLER_ADDR0 ((unsigned long)__builtin_return_address(0))
The only problem with this approach is what happens if the user changes
the enabled in between these two calls. This would make ftrace
inconsistent.
I have a patch from the -rt tree that handles what you want. It is
attached below. Not sure how well it will apply to mainline.
I really need to go through the rt patch set and start submitting a bunch
of clean-up/fixes to mainline. We've been meaning to do it, just have been
distracted :-(
-- Steve
From: Steven Rostedt <srostedt@...hat.com>
Subject: ftrace: cpu hotplug fix
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 | 23 +++++++++++++++++++++++
kernel/trace/trace_irqsoff.c | 3 +++
kernel/trace/trace_sched_wakeup.c | 2 +-
5 files changed, 44 insertions(+), 4 deletions(-)
Index: linux-2.6.26/include/linux/ftrace.h
===================================================================
--- linux-2.6.26.orig/include/linux/ftrace.h
+++ linux-2.6.26/include/linux/ftrace.h
@@ -33,10 +33,15 @@ void clear_ftrace_function(void);
extern void ftrace_stub(unsigned long a0, unsigned long a1);
+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-2.6.26/kernel/cpu.c
===================================================================
--- linux-2.6.26.orig/kernel/cpu.c
+++ linux-2.6.26/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);
@@ -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-2.6.26/kernel/trace/ftrace.c
===================================================================
--- linux-2.6.26.orig/kernel/trace/ftrace.c
+++ linux-2.6.26/kernel/trace/ftrace.c
@@ -151,6 +151,29 @@ static int __unregister_ftrace_function(
return ret;
}
+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-2.6.26/kernel/trace/trace_irqsoff.c
===================================================================
--- linux-2.6.26.orig/kernel/trace/trace_irqsoff.c
+++ linux-2.6.26/kernel/trace/trace_irqsoff.c
@@ -77,6 +77,9 @@ 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-2.6.26/kernel/trace/trace_sched_wakeup.c
===================================================================
--- linux-2.6.26.orig/kernel/trace/trace_sched_wakeup.c
+++ linux-2.6.26/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();
--
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