linux-kernel - Re: [GIT PULL] tracing/kprobes: Add dynamic tracepoints + instruction decoder

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Date:	Thu, 27 Aug 2009 13:32:53 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [GIT PULL] tracing/kprobes: Add dynamic tracepoints +	instruction
 decoder

Frederic Weisbecker wrote:
> On Thu, Aug 27, 2009 at 11:00:38AM -0400, Masami Hiramatsu wrote:
>> Frederic Weisbecker wrote:
>>> Ingo,
>>>
>>> This is the kprobes tracing pile of patches. I've tested it
>>> successfully by setting some kprobes through debugfs by hand.
>>>
>>> It brings no known regressions.
>>>
>>> However, the stress test provided by Masami have revealed some
>>> unstable points. Some symbols are unsafe to probe and raise
>>> probing recursion.
>>>
>>> I've added a tiny patch in the series that helps identifying the
>>> kprobe that has raised such situation.
>>> For example it has learned me today that it's unsafe to trace
>>> ret_from_exception() (obviously: it's on the int 3 handler path).
>>
>> Thank you, Frederic.
>>
>> I'm currently fixing those problems on x86-64 (on kvm).
>> I'll also check it on x86-32, and fix it.
>>
>> Thanks
>
>
>
> Cool.
> Don't hesitate to interate through small patches that fix these
> sites.
>
> So that I can continue to test it over time and report you what I find,
> may be I can try to fix some of them too.
>
> I haven't fixed ret_from_exception because I wasn't sure about the
> right thing to do: putting it in the kprobes section or blacklist its
> name. It's a bit more delicate to put assembly code into sections so... :)

It depends on implementation, but I think blacklist is the last resort. :)
AFAIK, some assembly codes are already pushed into kprobes section.

Thank you,

-- 
Masami Hiramatsu

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

e-mail: mhiramat@...hat.com

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