linux-kernel - Re: [PATCH v15 09/12] perf record: Read from overwritable ring buffer

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Date:	Wed, 13 Jul 2016 16:07:10 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	acme@...nel.org, lizefan@...wei.com, linux-kernel@...r.kernel.org,
	pi3orama@....com, He Kuang <hekuang@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Nilay Vaish <nilayvaish@...il.com>
Subject: Re: [PATCH v15 09/12] perf record: Read from overwritable ring buffer

On Tue, Jul 12, 2016 at 10:00:09AM +0000, Wang Nan wrote:

SBIP

> +		default:
> +			goto state_err;
> +		}
> +		break;
> +	}
> +	default:
> +		WARN_ONCE(1, "Shouldn't get there\n");
> +	}
> +
> +	rec->overwrite_evt_state = state;
> +
> +	switch (action) {
> +	case PAUSE:
> +		perf_evlist__pause(rec->evlist);
> +		break;
> +	case RESUME:
> +		perf_evlist__resume(rec->evlist);
> +		break;

so this is called on evlist with uninitialized backward_mmap,
which makes above calls fail, but luckily we dont check the
return values

I think we could set some evlist flag to know we have backward
mmaps and skip this function completely if we dont have any

thanks,
jirka