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Re: [tip:perf/urgent] perf/core: Fix the perf_cpu_time_max_percent check

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  Re: [tip:perf/urgent] perf/core: Fix the perf_cpu_time_max_percent  check Vince Weaver <vincent.weaver@maine.edu> - 2017-03-13 19:40 +0100
    Re: [tip:perf/urgent] perf/core: Fix the perf_cpu_time_max_percent  check Tan Xiaojun <tanxiaojun@huawei.com> - 2017-03-14 03:00 +0100

#1599678 — Re: [tip:perf/urgent] perf/core: Fix the perf_cpu_time_max_percent check

On Sat, 25 Feb 2017, Peter Zijlstra wrote:

> On Sat, Feb 25, 2017 at 04:10:37PM +0800, Tan Xiaojun wrote:
> 
> > 2)If it is, where we will fix it more appropriate, perf_fuzzer(not set
> > 0 or 100) or kernel(limit 1 to 99), or maybe it is the bug of
> > hardware(too many hardware interruptions)?
> 
> I think the best would be if the fuzzer would not set 0,100, those are
> clearly 'unsafe' settings and you pretty much get to keep the pieces.
> 
> I would like to preserve these settings for people that 'know' what
> they're doing and are willing to take the risk, but clearly, when you
> take the guard-rails off, things can come apart.

sorry for the delay responding, these e-mails ended up in the spam folder
somehow.

I could add a new "avoid stupid things as root" flag for the perf_fuzzer.

Besides this issue, are there other known things to skip?

Generally running a fuzzer as root can be a bad idea which is why I don't 
test that use case very often.
I think there were other issues in the past, like certain ftrace 
combinations being known to lock the system.

Vince

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#1599982

On 2017/3/14 2:35, Vince Weaver wrote:
> On Sat, 25 Feb 2017, Peter Zijlstra wrote:
> 
>> On Sat, Feb 25, 2017 at 04:10:37PM +0800, Tan Xiaojun wrote:
>>
>>> 2)If it is, where we will fix it more appropriate, perf_fuzzer(not set
>>> 0 or 100) or kernel(limit 1 to 99), or maybe it is the bug of
>>> hardware(too many hardware interruptions)?
>>
>> I think the best would be if the fuzzer would not set 0,100, those are
>> clearly 'unsafe' settings and you pretty much get to keep the pieces.
>>
>> I would like to preserve these settings for people that 'know' what
>> they're doing and are willing to take the risk, but clearly, when you
>> take the guard-rails off, things can come apart.
> 
> sorry for the delay responding, these e-mails ended up in the spam folder
> somehow.
> 
> I could add a new "avoid stupid things as root" flag for the perf_fuzzer.
> 
> Besides this issue, are there other known things to skip?
> 
> Generally running a fuzzer as root can be a bad idea which is why I don't 
> test that use case very often.
> I think there were other issues in the past, like certain ftrace 
> combinations being known to lock the system.
> 
> Vince
> 

It would be better if you could add such a flag to the perf_fuzzer. And I
have not found any other problems yet.

By the way. Use Non-root user to test is OK, and they do not have permission
to configure these parameters.

Thank you for your reply.

Xiaojun.

> .
> 

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