Re: perf, kprobes: fuzzer generates huge number of WARNings

[Vince Weaver]

On Tue, 7 Jul 2015, Masami Hiramatsu wrote:

> On 2015/07/07 6:27, Vince Weaver wrote:
> > Hello
> > 
> > I've been working on trying to get the perf_fuzzer to start fuzzing the 
> > PERF_EVENT_IOC_SET_BPF so I've added some really hackish kprobe support.
> > 
> > However before I can get to the BPF testing the kprobe code generates a 
> > constant stream of WARNINGS which make the machine more or less useless 
> > until I stop it.  I've included a small selection here.
> > 
> > Is this expected?
> 
> Did you get same message without BPF hack? And also, could you tell us
> your kernel version and configuration?

It's a Hawell machine running 4.2-rc1.  I can post the .config if it's of 
interest.

Well the BPF hack is in the fuzzer, not the kernel.  And it's not really a 
hack, it just turned out to be a huge pain to figure out how to 
manually create a valid BPF program in conjunction with a valid kprobe 
event.

I did have to sprinkle printks in the kprobe and bpf code to find out 
where various EINVAL returns were coming from, so potentially this is just 
a problem of printks happening where they shouldn't.  I'll remove those 
changes and try to reproduce this tomorrow.

This is possibly a long standing issue, until now I never ran the fuzzer 
as root so these particular code paths weren't tested.

Vince
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