Re: Bug with jprobes and function graph tracer

Masami Hiramatsu
2015-01-13T11:39:41Z

(2015/01/09 2:20), Steven Rostedt wrote:
> Hi Masami,
>
> First, I would like to wish you a Happy New Year :-)

Happy New Year! :)

> OK, now back to business.
>
>
> It has come to my attention that jprobes and function graph tracing do
> not play nicely together. I think you once told me they have issues as
> well.
>
> A simple way to test this is to load the jprobe_example.ko module and
> then run function graph tracing.

I see. Jprobes will mess up the function call path.

> Should we try to fix this? Or should it just be that users need to know
> not to enable the two together. Or we can prevent one from starting if
> the other is being used.

Yeah we should try to fix this, but not so high priority since jprobe
is not used so frequently. I guess one easy solution is adding notrace
to all jprobe handlers for hiding it from function-graph tracer.
If there is a way to check a function is notrace or not, I can use that
in register_jprobe and reject it if the handler is not "notrace"ed. :)

Thank you,

>
> Looking forward to hearing your thoughts on the subject.
>
> -- Steve
>

--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com