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SubjectRe: [PATCH -tip v4 0/6] kprobes: introduce NOKPROBE_SYMBOL() and fixes crash bugs

* 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


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