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Re: [PATCH -tip v4 0/6] kprobes: introduce NOKPROBE_SYMBOL() and fixes crash bugs
- From: Sandeepa Prabhu <sandeepa dot prabhu at linaro dot org>
- To: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>
- Cc: Ingo Molnar <mingo at kernel dot org>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, 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, 6 Dec 2013 12:24:29 +0530
- 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> <CA+b37P1ejFn4YJekJFOCe701mLTprqQi4KSyGV4S7QiVaC1=qA at mail dot gmail dot com> <52A16D49 dot 9050105 at hitachi dot com>
>> I am not sure if this question is related, uprobes or ftrace code does
>> not define __kprobes, so is it safe to place kprobe on uprobes or
>> ftrace code?
>
> Yes, it is "safe" in qualitative meaning. But for ftrace code, it could
> give a performance impact by miss-hitting. Since uprobe is independent
> from kprobe, it should work.
>
>> Is it expected from arch code to support such cases?
>
> Yes, the arch dependent implementation is the key. If it shares some
> code which can be called from miss-hit path, it should be blacklisted.
well, isn't the blacklist only for those routines that can not be
handled or may crash kernel, like the code sections called from
exception kprobes exception handlers etc?
suppose if the probe on routine can miss-hit (probes re-cursing) but
can be handled, it's only a quantitative issue (i.e. performance
impact) so it should be *user's* problem right? I mean, as you said
earlier about having white-list or a performance gatekeeper
(systemtap), one can avoid such cases by white list or removing
miss-hit probes dynamically. But a blacklisting a symbol means
placing a probe on that *can not be handled* and can crash the system,
is it correct?
Thanks,
Sandeepa
>
> Thank you,
>
> --
> Masami HIRAMATSU
> IT Management Research Dept. Linux Technology Center
> Hitachi, Ltd., Yokohama Research Laboratory
> E-mail: masami.hiramatsu.pt@hitachi.com
>
>