* [PATCH] tracing, sched: mark preempt_schedule() notrace
@ 2009-08-18 8:01 Lai Jiangshan
2009-08-18 10:38 ` Frederic Weisbecker
0 siblings, 1 reply; 5+ messages in thread
From: Lai Jiangshan @ 2009-08-18 8:01 UTC (permalink / raw)
To: Ingo Molnar, Steven Rostedt, Frederic Weisbecker, LKML
Current preempt_schedule() is not marked notrace. It may be
infinite recursion in __trace_graph_return().
preempt_schedule()
__trace_graph_return()
ftrace_preempt_disable() (!!return false!!)
ftrace_preempt_enable()
preempt_enable_notrace()
preempt_schedule() (need_resched() may be true again)
It hardly happens, but marking preempt_schedule() notrace
makes it safer.
One interesting thing is that preempt_schedule() is in
the blacklist of kprobe subsystem. "__kprobes" implies "notrace".
But preempt_schedule() cannot be marked __kprobes for it
has been marked __sched. It is in the blacklist makes me
consider this: should it be marked "notrace" -- YES.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
diff --git a/kernel/sched.c b/kernel/sched.c
index 5184580..2e9e209 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5534,7 +5534,7 @@ out:
* off of preempt_enable. Kernel preemptions off return from interrupt
* occur there and call schedule directly.
*/
-asmlinkage void __sched preempt_schedule(void)
+asmlinkage void __sched notrace preempt_schedule(void)
{
struct thread_info *ti = current_thread_info();
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] tracing, sched: mark preempt_schedule() notrace
2009-08-18 8:01 [PATCH] tracing, sched: mark preempt_schedule() notrace Lai Jiangshan
@ 2009-08-18 10:38 ` Frederic Weisbecker
2009-08-18 16:28 ` Steven Rostedt
2009-08-19 2:33 ` Lai Jiangshan
0 siblings, 2 replies; 5+ messages in thread
From: Frederic Weisbecker @ 2009-08-18 10:38 UTC (permalink / raw)
To: Lai Jiangshan; +Cc: Ingo Molnar, Steven Rostedt, LKML
On Tue, Aug 18, 2009 at 04:01:57PM +0800, Lai Jiangshan wrote:
>
> Current preempt_schedule() is not marked notrace. It may be
> infinite recursion in __trace_graph_return().
>
> preempt_schedule()
> __trace_graph_return()
> ftrace_preempt_disable() (!!return false!!)
> ftrace_preempt_enable()
> preempt_enable_notrace()
> preempt_schedule() (need_resched() may be true again)
It would happen in __trace_graph_return() , when preempt_schedule()
has finished its job. It's very unlikely the TIF_NEED_RESCHED is
set just after (because it has just been cleared).
But why not. In that case, preempt_schedule() is called again but it's
not a real tracing recursion.
That seems like a normal behaviour actually.
>
> It hardly happens, but marking preempt_schedule() notrace
> makes it safer.
>
> One interesting thing is that preempt_schedule() is in
> the blacklist of kprobe subsystem. "__kprobes" implies "notrace".
> But preempt_schedule() cannot be marked __kprobes for it
> has been marked __sched. It is in the blacklist makes me
> consider this: should it be marked "notrace" -- YES.
>
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> ---
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 5184580..2e9e209 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -5534,7 +5534,7 @@ out:
> * off of preempt_enable. Kernel preemptions off return from interrupt
> * occur there and call schedule directly.
> */
> -asmlinkage void __sched preempt_schedule(void)
> +asmlinkage void __sched notrace preempt_schedule(void)
> {
> struct thread_info *ti = current_thread_info();
>
>
>
>
>
>
>
>
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] tracing, sched: mark preempt_schedule() notrace
2009-08-18 10:38 ` Frederic Weisbecker
@ 2009-08-18 16:28 ` Steven Rostedt
2009-08-19 3:07 ` Lai Jiangshan
2009-08-19 2:33 ` Lai Jiangshan
1 sibling, 1 reply; 5+ messages in thread
From: Steven Rostedt @ 2009-08-18 16:28 UTC (permalink / raw)
To: Frederic Weisbecker; +Cc: Lai Jiangshan, Ingo Molnar, LKML
On Tue, 18 Aug 2009, Frederic Weisbecker wrote:
> On Tue, Aug 18, 2009 at 04:01:57PM +0800, Lai Jiangshan wrote:
> >
> > Current preempt_schedule() is not marked notrace. It may be
> > infinite recursion in __trace_graph_return().
> >
> > preempt_schedule()
> > __trace_graph_return()
> > ftrace_preempt_disable() (!!return false!!)
> > ftrace_preempt_enable()
> > preempt_enable_notrace()
> > preempt_schedule() (need_resched() may be true again)
>
>
>
> It would happen in __trace_graph_return() , when preempt_schedule()
> has finished its job. It's very unlikely the TIF_NEED_RESCHED is
> set just after (because it has just been cleared).
> But why not. In that case, preempt_schedule() is called again but it's
> not a real tracing recursion.
>
> That seems like a normal behaviour actually.
In fact, this is actually something to be traced. I would not add a
notrace to it. This is not saving anything, the trace_graph_return does
not need to worry about stack overflow, since the return code already
freed the stack.
-- Steve
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] tracing, sched: mark preempt_schedule() notrace
2009-08-18 10:38 ` Frederic Weisbecker
2009-08-18 16:28 ` Steven Rostedt
@ 2009-08-19 2:33 ` Lai Jiangshan
1 sibling, 0 replies; 5+ messages in thread
From: Lai Jiangshan @ 2009-08-19 2:33 UTC (permalink / raw)
To: Frederic Weisbecker; +Cc: Ingo Molnar, Steven Rostedt, LKML
Frederic Weisbecker wrote:
> On Tue, Aug 18, 2009 at 04:01:57PM +0800, Lai Jiangshan wrote:
>> Current preempt_schedule() is not marked notrace. It may be
>> infinite recursion in __trace_graph_return().
>>
>> preempt_schedule()
>> __trace_graph_return()
>> ftrace_preempt_disable() (!!return false!!)
>> ftrace_preempt_enable()
>> preempt_enable_notrace()
>> preempt_schedule() (need_resched() may be true again)
>
>
>
> It would happen in __trace_graph_return() , when preempt_schedule()
> has finished its job. It's very unlikely the TIF_NEED_RESCHED is
> set just after (because it has just been cleared).
It hardly happen ...
This doesn't mean it'll never happen.
> But why not. In that case, preempt_schedule() is called again but it's
> not a real tracing recursion.
>
> That seems like a normal behaviour actually.
>
>
It's not normal behavior, preempt_schedule() will not call
preempt_schedule() recursively in any situation when trace is off.
Here, preempt_schedule() is called from __trace_graph_return()
when trace_function_graph is on.
preempt_schedule()
__trace_graph_return()
preempt_schedule()
__trace_graph_return()
....
So, it's a real tracing recursion.
It hurts the stack.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] tracing, sched: mark preempt_schedule() notrace
2009-08-18 16:28 ` Steven Rostedt
@ 2009-08-19 3:07 ` Lai Jiangshan
0 siblings, 0 replies; 5+ messages in thread
From: Lai Jiangshan @ 2009-08-19 3:07 UTC (permalink / raw)
To: Steven Rostedt; +Cc: Frederic Weisbecker, Ingo Molnar, LKML
Steven Rostedt wrote:
>
> On Tue, 18 Aug 2009, Frederic Weisbecker wrote:
>
>> On Tue, Aug 18, 2009 at 04:01:57PM +0800, Lai Jiangshan wrote:
>>> Current preempt_schedule() is not marked notrace. It may be
>>> infinite recursion in __trace_graph_return().
>>>
>>> preempt_schedule()
>>> __trace_graph_return()
>>> ftrace_preempt_disable() (!!return false!!)
>>> ftrace_preempt_enable()
>>> preempt_enable_notrace()
>>> preempt_schedule() (need_resched() may be true again)
>>
>>
>> It would happen in __trace_graph_return() , when preempt_schedule()
>> has finished its job. It's very unlikely the TIF_NEED_RESCHED is
>> set just after (because it has just been cleared).
>> But why not. In that case, preempt_schedule() is called again but it's
>> not a real tracing recursion.
>>
>> That seems like a normal behaviour actually.
>
> In fact, this is actually something to be traced. I would not add a
> notrace to it. This is not saving anything, the trace_graph_return does
> not need to worry about stack overflow, since the return code already
> freed the stack.
>
You're right, I forgot to read trace_graph_return().
trace_graph_return() protects itself from recursion.
Since there is no may-recursive trace_func_graph_ret_t.
Just omit this patch.
Sorry for bothered you all.
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2009-08-19 3:08 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2009-08-18 8:01 [PATCH] tracing, sched: mark preempt_schedule() notrace Lai Jiangshan
2009-08-18 10:38 ` Frederic Weisbecker
2009-08-18 16:28 ` Steven Rostedt
2009-08-19 3:07 ` Lai Jiangshan
2009-08-19 2:33 ` Lai Jiangshan
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