linux-kernel - Re: Bug with jprobes and function graph tracer

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Message-ID: <54B503F5.4020509@hitachi.com>
Date:	Tue, 13 Jan 2015 20:39:33 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, vvs@...ru
Subject: Re: Bug with jprobes and function graph tracer

(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@...achi.com


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