Re: [PATCH v3 3/4] perf/bpf: Allow a bpf program to suppress all sample side effects

[Song Liu]

On Sun, Dec 10, 2023 at 8:56 PM Kyle Huey <me@xxxxxxxxxxxx> wrote:
>
> Returning zero from a bpf program attached to a perf event already
> suppresses any data output. Return early from __perf_event_overflow() in
> this case so it will also suppress event_limit accounting, SIGTRAP
> generation, and F_ASYNC signalling.
>
> Signed-off-by: Kyle Huey <khuey@xxxxxxxxxxxx>

Acked-by: Song Liu <song@xxxxxxxxxx>

> ---
>  kernel/events/core.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 54f6372d2634..d6093fe893c8 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -9541,6 +9541,11 @@ static int __perf_event_overflow(struct perf_event *event,
>
>         ret = __perf_event_account_interrupt(event, throttle);
>
> +#ifdef CONFIG_BPF_SYSCALL
> +       if (event->prog && !bpf_overflow_handler(event, data, regs))
> +               return ret;
> +#endif
> +
>         /*
>          * XXX event_limit might not quite work as expected on inherited
>          * events
> @@ -9590,10 +9595,7 @@ static int __perf_event_overflow(struct perf_event *event,
>                 irq_work_queue(&event->pending_irq);
>         }
>
> -#ifdef CONFIG_BPF_SYSCALL
> -       if (!(event->prog && !bpf_overflow_handler(event, data, regs)))
> -#endif
> -               READ_ONCE(event->overflow_handler)(event, data, regs);
> +       READ_ONCE(event->overflow_handler)(event, data, regs);
>
>         if (*perf_event_fasync(event) && event->pending_kill) {
>                 event->pending_wakeup = 1;
> --
> 2.34.1
>
>