On Mon, 17 May 2010, Stephane Eranian wrote:
> In case the sampling buffer has no "payload" pages, nr_pages is 0.
> The problem is that the error path in perf_output_begin() skips to
> a label which assumes perf_output_lock() has been issued which is
> not the case. That triggers a WARN_ON() is perf_output_unlock().
>
> This patch fixes the problem by adding a new label and skipping
> perf_task_unlock() in case data->nr_pages is 0.
It does? Your code looks good to me, but the description above is
a little flawed, since no new label is added.
Thanks
>
> Signed-off-by: Stephane Eranian <eran...@google.com>
>
> --
> diff --git a/kernel/perf_event.c b/kernel/perf_event.c
> index a4fa381..95137b6 100644
> --- a/kernel/perf_event.c
> +++ b/kernel/perf_event.c
> @@ -3035,8 +3035,10 @@ int perf_output_begin(struct perf_output_handle
> *handle,
> handle->nmi = nmi;
> handle->sample = sample;
>
> - if (!data->nr_pages)
> - goto fail;
> + if (!data->nr_pages) {
> + atomic_inc(&data->lost);
> + goto out;
> + }
>
> have_lost = atomic_read(&data->lost);
> if (have_lost)
> --
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