This is the mail archive of the
systemtap@sourceware.org
mailing list for the systemtap project.
Re: [PATCH -tip v4 0/6] kprobes: introduce NOKPROBE_SYMBOL() and fixes crash bugs
- From: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>
- To: Ingo Molnar <mingo at kernel dot org>
- Cc: Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Sandeepa Prabhu <sandeepa dot prabhu at linaro dot org>, x86 at kernel dot org, lkml <linux-kernel at vger dot kernel dot org>, "Steven Rostedt (Red Hat)" <rostedt at goodmis dot org>, systemtap at sourceware dot org, "David S. Miller" <davem at davemloft dot net>
- Date: Fri, 06 Dec 2013 11:34:30 +0900
- Subject: Re: [PATCH -tip v4 0/6] kprobes: introduce NOKPROBE_SYMBOL() and fixes crash bugs
- Authentication-results: sourceware.org; auth=none
- References: <20131204012841 dot 22118 dot 82992 dot stgit at kbuild-fedora dot novalocal> <20131204084551 dot GA31772 at gmail dot com> <529FBA71 dot 6070107 at hitachi dot com> <20131205102127 dot GA19923 at gmail dot com>
(2013/12/05 19:21), Ingo Molnar wrote:
>
> * Masami Hiramatsu <masami.hiramatsu.pt@hitachi.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@hitachi.com