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Date:   Wed, 11 Apr 2018 14:04:47 +0200
From:   Ingo Molnar <mingo@kernel.org>
To:     Song Liu <songliubraving@fb.com>
Cc:     Vince Weaver <vincent.weaver@maine.edu>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: perf: fuzzer leads to trace_kprobe: Could not insert message
 flood
Message-ID: <20180411120447.2gzrwijrtayjv3eg@gmail.com>
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* Song Liu <songliubraving@fb.com> wrote:

> 
> 
> > On Apr 10, 2018, at 7:48 AM, Vince Weaver <vincent.weaver@maine.edu> wrote:
> > 
> > Author: Song Liu <songliubraving@fb.com>
> > Date:   Wed Dec 6 14:45:15 2017 -0800
> > 
> > When running the perf_fuzzer on a current git checkout my logs are flooded 
> > with messages such as this:
> > [71487.869077] trace_kprobe: Could not insert probe at unknown+0: -22
> > [71488.174479] trace_kprobe: Could not insert probe at unknown+0: -22
> > 
> > Presumably this is due to the introduction of the perf_kprobe PMU in
> > 	commit e12f03d7031a977356e3d7b75a68c2185ff8d155
> > 	Author: Song Liu <songliubraving@fb.com>
> > 	Date:   Wed Dec 6 14:45:15 2017 -0800
> > 
> > Is there a way to get this error disabled, or else rate-limited?
> > 
> > Vince
> 
> Hi Vince, 
> 
> Thanks for the report. 
> 
> This is a new API that creates probe together with perf_event_open(). Based on 
> my limited understanding of perf_fuzzer, it doesn't understand this API, and uses 
> it in an abnormal way. [...]

Vince's point is valid: the kernel log should not be flooded with pointless 
messages as a response to user-space ABI uses ...

Why is there a kernel log message at all, isn't an error returned?

> [...] I would recommend perf_fuzzer to understand this new API and test it. 
> [...]

This bug needs to be fixed: a new API must not effectively DoS fuzzing efforts by 
spamming the kernel log ...

Thanks,

	Ingo