On Tue, Jul 23, 2013 at 02:31:00AM +0200, Frederic Weisbecker wrote:
> In case of allocation failure, get_callchain_buffer() keeps the
> refcount incremented for the current event.
>
> As a result, when get_callchain_buffers() returns an error,
> we must cleanup what it did by cancelling its last refcount
> with a call to put_callchain_buffers().
>
> This is a hack in order to be able to call free_event()
> after that failure.
>
> The original purpose of that was to simplify the failure
> path. But this error handling is actually counter intuitive,
> ugly and not very easy to follow because one expect to
> see the resources used to perform a service to be cleaned
> by the callee if case of failure, not by the caller.
>
> So lets clean this up by cancelling the refcount from
> get_callchain_buffer() in case of failure. And correctly free
> the event accordingly in perf_event_alloc().
>
> Signed-off-by: Frederic Weisbecker <[email protected]>
> Cc: Jiri Olsa <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Cc: Namhyung Kim <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Arnaldo Carvalho de Melo <[email protected]>
> Cc: Stephane Eranian <[email protected]>
> ---
> kernel/events/callchain.c | 2 ++
> kernel/events/core.c | 41 +++++++++++++++++++++--------------------
> 2 files changed, 23 insertions(+), 20 deletions(-)
>
> diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
> index c772061..76a8bc5 100644
> --- a/kernel/events/callchain.c
> +++ b/kernel/events/callchain.c
> @@ -117,6 +117,8 @@ int get_callchain_buffers(void)
> err = alloc_callchain_buffers();
> exit:
> mutex_unlock(&callchain_mutex);
> + if (err)
> + atomic_dec(&nr_callchain_events);
shouldn't we touch this under above lock?
also that above hunk decrements nr_callchain_events
also for following case:
count = atomic_inc_return(&nr_callchain_events);
if (WARN_ON_ONCE(count < 1)) {
err = -EINVAL;
goto exit;
}
seems like it screws the count
jirka
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