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Date: Wed, 6 Jul 2016 13:38:57 +0200
From: Jiri Olsa <jolsa@redhat.com>
To: Wang Nan <wangnan0@huawei.com>
Cc: acme@kernel.org, linux-kernel@vger.kernel.org, pi3orama@163.com,
        lizefan@huawei.com, He Kuang <hekuang@huawei.com>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Jiri Olsa <jolsa@kernel.org>, Masami Hiramatsu <mhiramat@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>, Nilay Vaish <nilayvaish@gmail.com>
Subject: Re: [PATCH v13 5/8] perf record: Read from overwritable ring buffer
Message-ID: <20160706113857.GD26517@krava>
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On Mon, Jul 04, 2016 at 06:20:06AM +0000, Wang Nan wrote:

SNIP

> +static void
> +record__toggle_overwrite_evsels(struct record *rec,
> +				enum overwrite_evt_state state)
> +{
> +	struct perf_evlist *evlist = rec->overwrite_evlist;
> +	enum overwrite_evt_state old_state = rec->overwrite_evt_state;
> +	enum action {
> +		NONE,
> +		PAUSE,
> +		RESUME,
> +	} action = NONE;
> +
> +	switch (old_state) {
> +	case OVERWRITE_EVT_RUNNING: {
> +		switch (state) {
> +		case OVERWRITE_EVT_DATA_PENDING:
> +			action = PAUSE;
> +			break;
> +		case OVERWRITE_EVT_RUNNING:
> +		case OVERWRITE_EVT_EMPTY:
> +		default:
> +			goto state_err;
> +		}
> +		break;
> +	}
> +	case OVERWRITE_EVT_DATA_PENDING: {
> +		switch (state) {
> +		case OVERWRITE_EVT_EMPTY:
> +			break;
> +		case OVERWRITE_EVT_RUNNING:
> +		case OVERWRITE_EVT_DATA_PENDING:
> +		default:
> +			goto state_err;
> +		}
> +		break;
> +	}
> +	case OVERWRITE_EVT_EMPTY: {
> +		switch (state) {
> +		case OVERWRITE_EVT_RUNNING:
> +			action = RESUME;
> +			break;
> +		case OVERWRITE_EVT_EMPTY:
> +		case OVERWRITE_EVT_DATA_PENDING:
> +		default:
> +			goto state_err;
> +		}
> +		break;
> +	}
> +	default:
> +		WARN_ONCE(1, "Shouldn't get there\n");
> +	}
> +
> +	rec->overwrite_evt_state = state;
> +
> +	if (!evlist)
> +		return;

I'd expect this check at the begining

jirka