linux-kernel - Re: [PATCH] perf record: handle death by SIGTERM

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Date:	Wed, 8 May 2013 08:54:47 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	David Ahern <dsahern@...il.com>
Cc:	Stephane Eranian <eranian@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	LKML <linux-kernel@...r.kernel.org>,
	Mike Galbraith <efault@....de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH] perf record: handle death by SIGTERM


* David Ahern <dsahern@...il.com> wrote:

> On 5/7/13 12:29 AM, Ingo Molnar wrote:
> >
> >* Stephane Eranian <eranian@...gle.com> wrote:
> >
> >>This is a good fix. I have run into this infinite loop in perf report
> >>many times.
> >
> >Hm, perf record should really not assume much about the perf.data and
> >should avoid infinite loops ...
> >
> >So while making perf.data more consistent on SIGTERM is a nice fix, perf
> >report should be fixed as well to detect loops and such.
> >
> >Thanks,
> >
> >	Ingo
> >
> 
> This seems to do the trick:
> 
> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> index 326068a..e82646f 100644
> --- a/tools/perf/util/header.c
> +++ b/tools/perf/util/header.c
> @@ -2802,6 +2802,17 @@ int perf_session__read_header(struct
> perf_session *session, int fd)
>     if (perf_file_header__read(&f_header, header, fd) < 0)
>         return -EINVAL;
> 
> +   /*
> +    * sanity check that perf.data was written cleanly: data size
> +    * is initialized to 0 and updated only if the on_exit function
> +    * is run. If data size is still 0 then the file cannot be
> +    * processed.
> +    */
> +   if (f_header.data.size == 0) {
> +       pr_err("data size is 0. Was record properly terminated?\n");
> +       return -1;
> +   }

Hm, this detects the condition - but where does the looping come from?

Can it happen with a perf.data that 'seems' clean but is corrupted 
(because not fully written, buggy kernel just crashed, etc.).

In essence it would be _very_ nice if someone reproduced the looping and 
checked what to do to fix the looping itself. Or does the above
data.size == 0 check fully fix the looping under every possible state of a 
perf.data?

Thanks,

	Ingo
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