Re: [PATCH] perf: Fix AUX record suppression

[Ben Gainey]

Hi Alex

I was just wondering if this was expected to make 5.1? (I could not see
it in RC5)?

Thanks
Ben



On Fri, 2019-03-29 at 11:13 +0200, Alexander Shishkin wrote:
> Commit 1627314fb54a33e ("perf: Suppress AUX/OVERWRITE records") has
> an
> unintended side-effect of also suppressing all AUX records with no
> flags
> and non-zero size, so all the regular records in the full trace mode.
> This breaks some use cases for people.
>
> Fix this by restoring "regular" AUX records.
>
> Signed-off-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx
> >
> Fixes: 1627314fb54a33e ("perf: Suppress AUX/OVERWRITE records")
> Reported-by: Ben Gainey <Ben.Gainey@xxxxxxx>
> Tested-by: Ben Gainey <Ben.Gainey@xxxxxxx>
> CC: stable@xxxxxxxxxxxxxxx # v4.20+
> ---
>  kernel/events/ring_buffer.c | 33 +++++++++++++++------------------
>  1 file changed, 15 insertions(+), 18 deletions(-)
>
> diff --git a/kernel/events/ring_buffer.c
> b/kernel/events/ring_buffer.c
> index 678ccec60d8f..626256dc26c1 100644
> --- a/kernel/events/ring_buffer.c
> +++ b/kernel/events/ring_buffer.c
> @@ -455,24 +455,21 @@ void perf_aux_output_end(struct
> perf_output_handle *handle, unsigned long size)
>  rb->aux_head += size;
>  }
>
> -if (size || handle->aux_flags) {
> -/*
> - * Only send RECORD_AUX if we have something useful to
> communicate
> - *
> - * Note: the OVERWRITE records by themselves are not
> considered
> - * useful, as they don't communicate any *new*
> information,
> - * aside from the short-lived offset, that becomes
> history at
> - * the next event sched-in and therefore isn't useful.
> - * The userspace that needs to copy out AUX data in
> overwrite
> - * mode should know to use user_page::aux_head for the
> actual
> - * offset. So, from now on we don't output AUX records
> that
> - * have *only* OVERWRITE flag set.
> - */
> -
> -if (handle->aux_flags & ~(u64)PERF_AUX_FLAG_OVERWRITE)
> -perf_event_aux_event(handle->event, aux_head,
> size,
> -                     handle->aux_flags);
> -}
> +/*
> + * Only send RECORD_AUX if we have something useful to
> communicate
> + *
> + * Note: the OVERWRITE records by themselves are not considered
> + * useful, as they don't communicate any *new* information,
> + * aside from the short-lived offset, that becomes history at
> + * the next event sched-in and therefore isn't useful.
> + * The userspace that needs to copy out AUX data in overwrite
> + * mode should know to use user_page::aux_head for the actual
> + * offset. So, from now on we don't output AUX records that
> + * have *only* OVERWRITE flag set.
> + */
> +if (size || (handle->aux_flags &
> ~(u64)PERF_AUX_FLAG_OVERWRITE))
> +perf_event_aux_event(handle->event, aux_head, size,
> +     handle->aux_flags);
>
>  rb->user_page->aux_head = rb->aux_head;
>  if (rb_need_aux_wakeup(rb))
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