linux-kernel - Re: [PATCH -tip v4 0/6] kprobes: introduce NOKPROBE

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Message-ID: <52A137B6.6030307@hitachi.com>
Date:	Fri, 06 Dec 2013 11:34:30 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Sandeepa Prabhu <sandeepa.prabhu@...aro.org>, x86@...nel.org,
	lkml <linux-kernel@...r.kernel.org>,
	"Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
	systemtap@...rceware.org, "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH -tip v4 0/6] kprobes: introduce NOKPROBE_SYMBOL() and
 fixes crash bugs

(2013/12/05 19:21), Ingo Molnar wrote:
> 
> * Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:
> 
>>> So we need both a maintainable and a sane/safe solution, and I'd 
>>> like to apply the whole thing at once and be at ease that the 
>>> solution is round. We should have done this years ago.
>>
>> For the safeness of kprobes, I have an idea; introduce a whitelist 
>> for dynamic events. AFAICS, the biggest unstable issue of kprobes 
>> comes from putting *many* probes on the functions called from 
>> tracers.
> 
> If the number of 'noprobe' annotations is expected to explode then 
> maybe another approach should be considered.

No, since this is a "quantitative" issue, the annotation helps us.

> For example in perf we detect recursion. Could kprobes do that and 
> detect hitting a probe while running kprobes code, and ignore it [do 
> an early return]?

Yes, the kprobe itself already has recursion detector and it rejects
calling handler.

> 
> That way most of the annotations could be removed and kprobes would 
> become inherently safe. Is there any complication I'm missing?

That is actually what I'm doing with cleanup patches. :)


Thank you,

-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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