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Re: [PATCH -tip v4 0/6] kprobes: introduce NOKPROBE_SYMBOL() and fixes crash bugs
- From: Ingo Molnar <mingo at kernel dot org>
- To: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>
- 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: Tue, 10 Dec 2013 16:28:11 +0100
- 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> <52A137B6 dot 6030307 at hitachi dot com>
* Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> wrote:
> (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.
So why are annotations needed at all? What can happen if an annotation
is missing and a piece of code is probed which is also used by the
kprobes code internally - do we crash, lock up, misbehave or handle it
safely?
Thanks,
Ingo