linux-kernel - Re: BUG: perf top enters loop synthesizing events for existing threads

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Message-ID: <20150408141427.GE5403@kernel.org>
Date:	Wed, 8 Apr 2015 11:14:27 -0300
From:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:	David Ahern <dsahern@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Don Zickus <dzickus@...hat.com>, Jiri Olsa <jolsa@...nel.org>,
	Joe Mario <jmario@...hat.com>, Ingo Molnar <mingo@...nel.org>
Subject: Re: BUG: perf top enters loop synthesizing events for existing
 threads

Em Wed, Apr 08, 2015 at 07:48:23AM -0600, David Ahern escreveu:
> On 4/8/15 7:45 AM, Arnaldo Carvalho de Melo wrote:
> >>I also noticed that if I set /proc/sys/kernel/perf_event_paranoid to -1
> >>to run it as !root, then the problem "goes away", which I think probably
> >>is explained by, as !root, not being able to parse some of the /proc
> >>files for existing threads and thus not triggering the bug, still
> >>investigating...
> 
> odd. because this has nothing to do with perf_events; it is just walking
> /proc and for the ppid adds a strstr and atoi(str). Something else is at
> play. I'll take a look.

You are correcly setting the pid values, that will have effects when
using findnew, i.e. threads will be added to the rbtree, which causes
allocations, etc I.e. it is probably triggering a dormant bug

- Arnaldo
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