Re: [PATCH] perf_events: fix errors path in perf_output_begin()

[Stephane Eranian]

On Mon, May 17, 2010 at 1:04 PM, John Kacur <jkacur@xxxxxxxxxx> wrote:
>
>
> On Mon, 17 May 2010, Stephane Eranian wrote:
>
>> Â In case the sampling buffer has no "payload" pages, nr_pages is 0.
>> Â The problem is that the error path in perf_output_begin() skips to
>> Â a label which assumes perf_output_lock() has been issued which is
>> Â not the case. That triggers a WARN_ON() is perf_output_unlock().
>>
>> Â This patch fixes the problem by adding a new label and skipping
>> Â 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.
>
Sorry about that. I had written the text before the final version of the patch!
I will resubmit.

>> --
>> 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;
>> Â Â Â handle->sample Â= sample;
>>
>> - Â Â if (!data->nr_pages)
>> - Â Â Â Â Â Â goto fail;
>> + Â Â if (!data->nr_pages) {
>> + Â Â Â Â Â Â atomic_inc(&data->lost);
>> + Â Â Â Â Â Â goto out;
>> + Â Â }
>>
>> Â Â Â have_lost = atomic_read(&data->lost);
>> Â Â Â if (have_lost)
>> --
>
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