linux-kernel - Re: suspicious RCU usage (perf)

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Message-ID: <521CB074.3040900@gmail.com>
Date:	Tue, 27 Aug 2013 07:58:12 -0600
From:	David Ahern <dsahern@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Dave Jones <davej@...hat.com>, paulmck@...ux.vnet.ibm.com,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: suspicious RCU usage (perf)

On 8/27/13 7:10 AM, Steven Rostedt wrote:
> On Mon, 26 Aug 2013 15:49:24 -0400
> Dave Jones <davej@...hat.com> wrote:
>
>
>>   > Do you have /sys/kernel/debug with access permissions?
>>
>> Ah, yeah, that'll be it. Good catch.
>>
>> Sorry for the false alarm Steve ;)
>
> Yeah, but it still does not explain how perf got started. Perf requires
> a sys_perf_event_open() call to run.

Per Peter's response another option is the paranoia level:

# perf event paranoia level:
# -1 - not paranoid at all
#  0 - disallow raw tracepoint access for unpriv
#  1 - disallow cpu events for unpriv
#  2 - disallow kernel profiling for unpriv
kernel.perf_event_paranoid = -1

I keep my dev box at -1 and set /sys/kernel/debug to 755 to run perf as 
non-root.

David
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