[PATCH] tracing/ftrace: add missing wake-up on some callsites

[PATCH] tracing/ftrace: add missing wake-up on some callsites

[Frederic Weisbecker]

Impact: fix unwaken pipe

Now that we use a common wakeup infrastructure, we must append a wakeup
on few callsites which lack it or tasks reading trace_pipe will not be
awaken when events come on few tracers.

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
 kernel/trace/trace.c             |    2 ++
 kernel/trace/trace_branch.c      |    2 ++
 kernel/trace/trace_hw_branches.c |    2 ++
 3 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index e1f3b99..7f450b6 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3055,6 +3055,8 @@ int trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args)
  out:
 	preempt_enable_notrace();
 
+	trace_wake_up();
+
 	return len;
 }
 EXPORT_SYMBOL_GPL(trace_vprintk);
diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
index c2e68d4..8c8f8c0 100644
--- a/kernel/trace/trace_branch.c
+++ b/kernel/trace/trace_branch.c
@@ -78,6 +78,8 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
  out:
 	atomic_dec(&tr->data[cpu]->disabled);
 	local_irq_restore(flags);
+
+	trace_wake_up();
 }
 
 static inline
diff --git a/kernel/trace/trace_hw_branches.c b/kernel/trace/trace_hw_branches.c
index 3561aac..ddd87fd 100644
--- a/kernel/trace/trace_hw_branches.c
+++ b/kernel/trace/trace_hw_branches.c
@@ -202,6 +202,8 @@ void trace_hw_branch(u64 from, u64 to)
  out:
 	atomic_dec(&tr->data[cpu]->disabled);
 	local_irq_restore(irq1);
+
+	trace_wake_up();
 }
 
 static void trace_bts_at(const struct bts_trace *trace, void *at)
-- 
1.6.1

Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

[Ingo Molnar]

* Frederic Weisbecker <fweisbec@gmail.com> wrote:

> Impact: fix unwaken pipe
> 
> Now that we use a common wakeup infrastructure, we must append a wakeup
> on few callsites which lack it or tasks reading trace_pipe will not be
> awaken when events come on few tracers.
> 
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> ---
>  kernel/trace/trace.c             |    2 ++
>  kernel/trace/trace_branch.c      |    2 ++
>  kernel/trace/trace_hw_branches.c |    2 ++
>  3 files changed, 6 insertions(+), 0 deletions(-)

Applied to tip:tracing/ftrace, thanks Frederic!

	Ingo

Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

[Steven Rostedt]

On Sun, 22 Feb 2009, Frederic Weisbecker wrote:

> Impact: fix unwaken pipe
> 
> Now that we use a common wakeup infrastructure, we must append a wakeup
> on few callsites which lack it or tasks reading trace_pipe will not be
> awaken when events come on few tracers.
> 
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> ---
>  kernel/trace/trace.c             |    2 ++
>  kernel/trace/trace_branch.c      |    2 ++
>  kernel/trace/trace_hw_branches.c |    2 ++
>  3 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index e1f3b99..7f450b6 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3055,6 +3055,8 @@ int trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args)
>   out:
>  	preempt_enable_notrace();
>  
> +	trace_wake_up();
> +
>  	return len;
>  }
>  EXPORT_SYMBOL_GPL(trace_vprintk);
> diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
> index c2e68d4..8c8f8c0 100644
> --- a/kernel/trace/trace_branch.c
> +++ b/kernel/trace/trace_branch.c
> @@ -78,6 +78,8 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
>   out:
>  	atomic_dec(&tr->data[cpu]->disabled);
>  	local_irq_restore(flags);
> +
> +	trace_wake_up();
>  }
>  
>  static inline
> diff --git a/kernel/trace/trace_hw_branches.c b/kernel/trace/trace_hw_branches.c
> index 3561aac..ddd87fd 100644
> --- a/kernel/trace/trace_hw_branches.c
> +++ b/kernel/trace/trace_hw_branches.c
> @@ -202,6 +202,8 @@ void trace_hw_branch(u64 from, u64 to)
>   out:
>  	atomic_dec(&tr->data[cpu]->disabled);
>  	local_irq_restore(irq1);
> +
> +	trace_wake_up();
>  }
>  
>  static void trace_bts_at(const struct bts_trace *trace, void *at)

Ah, we don't wake up purposely on these three places. ftrace_printk is 
meant to be called anywhere (including the scheduler). And the branch 
tracers are also allowed to be called anywhere (they usually are).

Calling "wake_up" from any of these can easily cause a dead lock with the 
run queue lock, because all three can be called from with in the 
scheduler.

Sorry, but I have to NACK this change.

-- Steve

Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

[Steven Rostedt]

On Mon, 23 Feb 2009, Steven Rostedt wrote:

> 
> 
> On Sun, 22 Feb 2009, Frederic Weisbecker wrote:
> 
> > Impact: fix unwaken pipe
> > 
> > Now that we use a common wakeup infrastructure, we must append a wakeup
> > on few callsites which lack it or tasks reading trace_pipe will not be
> > awaken when events come on few tracers.
> > 
> > Cc: Steven Rostedt <rostedt@goodmis.org>
> > Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> > ---
> >  kernel/trace/trace.c             |    2 ++
> >  kernel/trace/trace_branch.c      |    2 ++
> >  kernel/trace/trace_hw_branches.c |    2 ++
> >  3 files changed, 6 insertions(+), 0 deletions(-)
> > 
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index e1f3b99..7f450b6 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -3055,6 +3055,8 @@ int trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args)
> >   out:
> >  	preempt_enable_notrace();
> >  
> > +	trace_wake_up();
> > +
> >  	return len;
> >  }
> >  EXPORT_SYMBOL_GPL(trace_vprintk);
> > diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
> > index c2e68d4..8c8f8c0 100644
> > --- a/kernel/trace/trace_branch.c
> > +++ b/kernel/trace/trace_branch.c
> > @@ -78,6 +78,8 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
> >   out:
> >  	atomic_dec(&tr->data[cpu]->disabled);
> >  	local_irq_restore(flags);
> > +
> > +	trace_wake_up();
> >  }
> >  
> >  static inline
> > diff --git a/kernel/trace/trace_hw_branches.c b/kernel/trace/trace_hw_branches.c
> > index 3561aac..ddd87fd 100644
> > --- a/kernel/trace/trace_hw_branches.c
> > +++ b/kernel/trace/trace_hw_branches.c
> > @@ -202,6 +202,8 @@ void trace_hw_branch(u64 from, u64 to)
> >   out:
> >  	atomic_dec(&tr->data[cpu]->disabled);
> >  	local_irq_restore(irq1);
> > +
> > +	trace_wake_up();
> >  }
> >  
> >  static void trace_bts_at(const struct bts_trace *trace, void *at)
> 
> Ah, we don't wake up purposely on these three places. ftrace_printk is 
> meant to be called anywhere (including the scheduler). And the branch 
> tracers are also allowed to be called anywhere (they usually are).
> 
> Calling "wake_up" from any of these can easily cause a dead lock with the 
> run queue lock, because all three can be called from with in the 
> scheduler.
> 
> Sorry, but I have to NACK this change.


Perhaps we could add these callsites back, but we would need to update 
trace_wake_up.

Have trace_wake_up set a flag instead, and add a tracepoint around the 
scheduler (outside the grabbing of runqueue locks), that will have a 
callback to the tracing code. That call back can perform the wakeups.

How does that sound?

-- Steve

Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

[Frederic Weisbecker]

On Mon, Feb 23, 2009 at 10:42:04AM -0500, Steven Rostedt wrote:
> 
> On Mon, 23 Feb 2009, Steven Rostedt wrote:
> 
> > 
> > 
> > On Sun, 22 Feb 2009, Frederic Weisbecker wrote:
> > 
> > > Impact: fix unwaken pipe
> > > 
> > > Now that we use a common wakeup infrastructure, we must append a wakeup
> > > on few callsites which lack it or tasks reading trace_pipe will not be
> > > awaken when events come on few tracers.
> > > 
> > > Cc: Steven Rostedt <rostedt@goodmis.org>
> > > Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> > > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> > > ---
> > >  kernel/trace/trace.c             |    2 ++
> > >  kernel/trace/trace_branch.c      |    2 ++
> > >  kernel/trace/trace_hw_branches.c |    2 ++
> > >  3 files changed, 6 insertions(+), 0 deletions(-)
> > > 
> > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > > index e1f3b99..7f450b6 100644
> > > --- a/kernel/trace/trace.c
> > > +++ b/kernel/trace/trace.c
> > > @@ -3055,6 +3055,8 @@ int trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args)
> > >   out:
> > >  	preempt_enable_notrace();
> > >  
> > > +	trace_wake_up();
> > > +
> > >  	return len;
> > >  }
> > >  EXPORT_SYMBOL_GPL(trace_vprintk);
> > > diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
> > > index c2e68d4..8c8f8c0 100644
> > > --- a/kernel/trace/trace_branch.c
> > > +++ b/kernel/trace/trace_branch.c
> > > @@ -78,6 +78,8 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
> > >   out:
> > >  	atomic_dec(&tr->data[cpu]->disabled);
> > >  	local_irq_restore(flags);
> > > +
> > > +	trace_wake_up();
> > >  }
> > >  
> > >  static inline
> > > diff --git a/kernel/trace/trace_hw_branches.c b/kernel/trace/trace_hw_branches.c
> > > index 3561aac..ddd87fd 100644
> > > --- a/kernel/trace/trace_hw_branches.c
> > > +++ b/kernel/trace/trace_hw_branches.c
> > > @@ -202,6 +202,8 @@ void trace_hw_branch(u64 from, u64 to)
> > >   out:
> > >  	atomic_dec(&tr->data[cpu]->disabled);
> > >  	local_irq_restore(irq1);
> > > +
> > > +	trace_wake_up();
> > >  }
> > >  
> > >  static void trace_bts_at(const struct bts_trace *trace, void *at)
> > 
> > Ah, we don't wake up purposely on these three places. ftrace_printk is 
> > meant to be called anywhere (including the scheduler). And the branch 
> > tracers are also allowed to be called anywhere (they usually are).
> > 
> > Calling "wake_up" from any of these can easily cause a dead lock with the 
> > run queue lock, because all three can be called from with in the 
> > scheduler.
> > 
> > Sorry, but I have to NACK this change.
> 
> 
> Perhaps we could add these callsites back, but we would need to update 
> trace_wake_up.
> 
> Have trace_wake_up set a flag instead, and add a tracepoint around the 
> scheduler (outside the grabbing of runqueue locks), that will have a 
> callback to the tracing code. That call back can perform the wakeups.
> 
> How does that sound?


That sounds good but only for these particular tracers I guess.

 
> -- Steve
> 

Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

[Steven Rostedt]

On Mon, 23 Feb 2009, Frederic Weisbecker wrote:
> > 
> > Perhaps we could add these callsites back, but we would need to update 
> > trace_wake_up.
> > 
> > Have trace_wake_up set a flag instead, and add a tracepoint around the 
> > scheduler (outside the grabbing of runqueue locks), that will have a 
> > callback to the tracing code. That call back can perform the wakeups.
> > 
> > How does that sound?
> 
> 
> That sounds good but only for these particular tracers I guess.

OK, what about making a trace_delay_wake_up()?

-- Steve

Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

[Frederic Weisbecker]

On Mon, Feb 23, 2009 at 11:51:30AM -0500, Steven Rostedt wrote:
> 
> On Mon, 23 Feb 2009, Frederic Weisbecker wrote:
> > > 
> > > Perhaps we could add these callsites back, but we would need to update 
> > > trace_wake_up.
> > > 
> > > Have trace_wake_up set a flag instead, and add a tracepoint around the 
> > > scheduler (outside the grabbing of runqueue locks), that will have a 
> > > callback to the tracing code. That call back can perform the wakeups.
> > > 
> > > How does that sound?
> > 
> > 
> > That sounds good but only for these particular tracers I guess.
> 
> OK, what about making a trace_delay_wake_up()?


Which would send a delayed work to wake up?

 
> -- Steve
> 

Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

[Steven Rostedt]

On Mon, 23 Feb 2009, Frederic Weisbecker wrote:

> On Mon, Feb 23, 2009 at 11:51:30AM -0500, Steven Rostedt wrote:
> > 
> > On Mon, 23 Feb 2009, Frederic Weisbecker wrote:
> > > > 
> > > > Perhaps we could add these callsites back, but we would need to update 
> > > > trace_wake_up.
> > > > 
> > > > Have trace_wake_up set a flag instead, and add a tracepoint around the 
> > > > scheduler (outside the grabbing of runqueue locks), that will have a 
> > > > callback to the tracing code. That call back can perform the wakeups.
> > > > 
> > > > How does that sound?
> > > 
> > > 
> > > That sounds good but only for these particular tracers I guess.
> > 
> > OK, what about making a trace_delay_wake_up()?
> 
> 
> Which would send a delayed work to wake up?

No, I was thinking that trace_delay_wake_up() would be called by these 
dangerous call sites. Then a per_cpu flag could be set. We could have a 
trace point in the scheduler code that is outside holding a runqueue lock, 
and this trace point would call a trace function that will clear the per 
cpu flag, and then call trace_wake_up().


-- Steve

Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

[Frederic Weisbecker]

On Mon, Feb 23, 2009 at 12:13:36PM -0500, Steven Rostedt wrote:
> 
> On Mon, 23 Feb 2009, Frederic Weisbecker wrote:
> 
> > On Mon, Feb 23, 2009 at 11:51:30AM -0500, Steven Rostedt wrote:
> > > 
> > > On Mon, 23 Feb 2009, Frederic Weisbecker wrote:
> > > > > 
> > > > > Perhaps we could add these callsites back, but we would need to update 
> > > > > trace_wake_up.
> > > > > 
> > > > > Have trace_wake_up set a flag instead, and add a tracepoint around the 
> > > > > scheduler (outside the grabbing of runqueue locks), that will have a 
> > > > > callback to the tracing code. That call back can perform the wakeups.
> > > > > 
> > > > > How does that sound?
> > > > 
> > > > 
> > > > That sounds good but only for these particular tracers I guess.
> > > 
> > > OK, what about making a trace_delay_wake_up()?
> > 
> > 
> > Which would send a delayed work to wake up?
> 
> No, I was thinking that trace_delay_wake_up() would be called by these 
> dangerous call sites. Then a per_cpu flag could be set. We could have a 
> trace point in the scheduler code that is outside holding a runqueue lock, 
> and this trace point would call a trace function that will clear the per 
> cpu flag, and then call trace_wake_up().
> 


Oh yes, sounds nice!

 
> -- Steve
> 

Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

[Ingo Molnar]

* Steven Rostedt <rostedt@goodmis.org> wrote:

> > Which would send a delayed work to wake up?
> 
> No, I was thinking that trace_delay_wake_up() would be called 
> by these dangerous call sites. Then a per_cpu flag could be 
> set. We could have a trace point in the scheduler code that is 
> outside holding a runqueue lock, and this trace point would 
> call a trace function that will clear the per cpu flag, and 
> then call trace_wake_up().

No, that's very roundabout and ugly. If we putting a tracepoint 
there we might as well put real scheduler code there that looks 
for such a flag. But i'm not convinced we need a flag ...

	Ingo

Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

[Steven Rostedt]

On Mon, 23 Feb 2009, Ingo Molnar wrote:

> 
> * Steven Rostedt <rostedt@goodmis.org> wrote:
> 
> > > Which would send a delayed work to wake up?
> > 
> > No, I was thinking that trace_delay_wake_up() would be called 
> > by these dangerous call sites. Then a per_cpu flag could be 
> > set. We could have a trace point in the scheduler code that is 
> > outside holding a runqueue lock, and this trace point would 
> > call a trace function that will clear the per cpu flag, and 
> > then call trace_wake_up().
> 
> No, that's very roundabout and ugly. If we putting a tracepoint 
> there we might as well put real scheduler code there that looks 
> for such a flag. But i'm not convinced we need a flag ...

Just a suggestion. I was trying to keep the tracer from being an overhead. 
But what else would you suggest? Just having the scheduler call 
trace_wakeup?

-- Steve

Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

[Ingo Molnar]

* Steven Rostedt <rostedt@goodmis.org> wrote:

> On Mon, 23 Feb 2009, Ingo Molnar wrote:
> 
> > * Steven Rostedt <rostedt@goodmis.org> wrote:
> > 
> > > > Which would send a delayed work to wake up?
> > > 
> > > No, I was thinking that trace_delay_wake_up() would be 
> > > called by these dangerous call sites. Then a per_cpu flag 
> > > could be set. We could have a trace point in the scheduler 
> > > code that is outside holding a runqueue lock, and this 
> > > trace point would call a trace function that will clear 
> > > the per cpu flag, and then call trace_wake_up().
> > 
> > No, that's very roundabout and ugly. If we putting a 
> > tracepoint there we might as well put real scheduler code 
> > there that looks for such a flag. But i'm not convinced we 
> > need a flag ...
> 
> Just a suggestion. I was trying to keep the tracer from being 
> an overhead. But what else would you suggest? Just having the 
> scheduler call trace_wakeup?

i think we could use a TIF flag to trigger a wakeup at the 
return-to-userspace (or return-from-IRQ) stage or so?

	Ingo

Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

[Masami Hiramatsu]

Steven Rostedt wrote:
> On Mon, 23 Feb 2009, Ingo Molnar wrote:
> 
>> * Steven Rostedt <rostedt@goodmis.org> wrote:
>>
>>>> Which would send a delayed work to wake up?
>>> No, I was thinking that trace_delay_wake_up() would be called 
>>> by these dangerous call sites. Then a per_cpu flag could be 
>>> set. We could have a trace point in the scheduler code that is 
>>> outside holding a runqueue lock, and this trace point would 
>>> call a trace function that will clear the per cpu flag, and 
>>> then call trace_wake_up().
>> No, that's very roundabout and ugly. If we putting a tracepoint 
>> there we might as well put real scheduler code there that looks 
>> for such a flag. But i'm not convinced we need a flag ...
> 
> Just a suggestion. I was trying to keep the tracer from being an overhead. 
> But what else would you suggest? Just having the scheduler call 
> trace_wakeup?

Actually, Systemtap(LTTng too?) also has same problem. Currently,
we're using a periodical timer to wake the reader process up.
I assume if we can put a tracepoint at the beginning of schedule(),
we can share it.

Thank you,


> 
> -- Steve
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com

Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

[Frederic Weisbecker]

On Mon, Feb 23, 2009 at 10:37:52AM -0500, Steven Rostedt wrote:
> 
> 
> On Sun, 22 Feb 2009, Frederic Weisbecker wrote:
> 
> > Impact: fix unwaken pipe
> > 
> > Now that we use a common wakeup infrastructure, we must append a wakeup
> > on few callsites which lack it or tasks reading trace_pipe will not be
> > awaken when events come on few tracers.
> > 
> > Cc: Steven Rostedt <rostedt@goodmis.org>
> > Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> > ---
> >  kernel/trace/trace.c             |    2 ++
> >  kernel/trace/trace_branch.c      |    2 ++
> >  kernel/trace/trace_hw_branches.c |    2 ++
> >  3 files changed, 6 insertions(+), 0 deletions(-)
> > 
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index e1f3b99..7f450b6 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -3055,6 +3055,8 @@ int trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args)
> >   out:
> >  	preempt_enable_notrace();
> >  
> > +	trace_wake_up();
> > +
> >  	return len;
> >  }
> >  EXPORT_SYMBOL_GPL(trace_vprintk);
> > diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
> > index c2e68d4..8c8f8c0 100644
> > --- a/kernel/trace/trace_branch.c
> > +++ b/kernel/trace/trace_branch.c
> > @@ -78,6 +78,8 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
> >   out:
> >  	atomic_dec(&tr->data[cpu]->disabled);
> >  	local_irq_restore(flags);
> > +
> > +	trace_wake_up();
> >  }
> >  
> >  static inline
> > diff --git a/kernel/trace/trace_hw_branches.c b/kernel/trace/trace_hw_branches.c
> > index 3561aac..ddd87fd 100644
> > --- a/kernel/trace/trace_hw_branches.c
> > +++ b/kernel/trace/trace_hw_branches.c
> > @@ -202,6 +202,8 @@ void trace_hw_branch(u64 from, u64 to)
> >   out:
> >  	atomic_dec(&tr->data[cpu]->disabled);
> >  	local_irq_restore(irq1);
> > +
> > +	trace_wake_up();
> >  }
> >  
> >  static void trace_bts_at(const struct bts_trace *trace, void *at)
> 
> Ah, we don't wake up purposely on these three places. ftrace_printk is 
> meant to be called anywhere (including the scheduler). And the branch 
> tracers are also allowed to be called anywhere (they usually are).
> 
> Calling "wake_up" from any of these can easily cause a dead lock with the 
> run queue lock, because all three can be called from with in the 
> scheduler.
> 
> Sorry, but I have to NACK this change.


And fortunately you NACK, I didn't realized how dangerous it can be.
I will send a patch to make these branch tracers use the old polling wake up.

But another solution should be found for ftrace_printk() since it doesn't necessarily
rely on any tracer.

 
> -- Steve