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Date: Wed, 13 Jul 2016 16:07:10 +0200
From: Jiri Olsa <jolsa@redhat.com>
To: Wang Nan <wangnan0@huawei.com>
Cc: acme@kernel.org, lizefan@huawei.com, linux-kernel@vger.kernel.org,
        pi3orama@163.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 v15 09/12] perf record: Read from overwritable ring buffer
Message-ID: <20160713140710.GE31742@krava>
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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