On Wed, 24 Mar 2021 at 15:01, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> One last try, I'll leave it alone now, I promise :-)
This looks like it does what you suggested, thanks! :-)
I'll still need to think about it, because of the potential problem
with modify-signal-races and what the user's synchronization story
would look like then.
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -778,6 +778,9 @@ struct perf_event {
> void *security;
> #endif
> struct list_head sb_list;
> +
> + unsigned long si_uattr;
> + unsigned long si_data;
> #endif /* CONFIG_PERF_EVENTS */
> };
>
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -5652,13 +5652,17 @@ static long _perf_ioctl(struct perf_even
> return perf_event_query_prog_array(event, (void __user *)arg);
>
> case PERF_EVENT_IOC_MODIFY_ATTRIBUTES: {
> + struct perf_event_attr __user *uattr;
> struct perf_event_attr new_attr;
> - int err = perf_copy_attr((struct perf_event_attr __user *)arg,
> - &new_attr);
> + int err;
>
> + uattr = (struct perf_event_attr __user *)arg;
> + err = perf_copy_attr(uattr, &new_attr);
> if (err)
> return err;
>
> + event->si_uattr = (unsigned long)uattr;
> +
> return perf_event_modify_attr(event, &new_attr);
> }
> default:
> @@ -6399,7 +6403,12 @@ static void perf_sigtrap(struct perf_eve
> clear_siginfo(&info);
> info.si_signo = SIGTRAP;
> info.si_code = TRAP_PERF;
> - info.si_errno = event->attr.type;
> + info.si_addr = (void *)event->si_data;
> +
> + info.si_perf = event->si_uattr;
> + if (event->parent)
> + info.si_perf = event->parent->si_uattr;
> +
> force_sig_info(&info);
> }
>
> @@ -6414,8 +6423,8 @@ static void perf_pending_event_disable(s
> WRITE_ONCE(event->pending_disable, -1);
>
> if (event->attr.sigtrap) {
> - atomic_set(&event->event_limit, 1); /* rearm event */
> perf_sigtrap(event);
> + atomic_set_release(&event->event_limit, 1); /* rearm event */
> return;
> }
>
> @@ -9121,6 +9130,7 @@ static int __perf_event_overflow(struct
> if (events && atomic_dec_and_test(&event->event_limit)) {
> ret = 1;
> event->pending_kill = POLL_HUP;
> + event->si_data = data->addr;
>
> perf_event_disable_inatomic(event);
> }
> @@ -12011,6 +12021,8 @@ SYSCALL_DEFINE5(perf_event_open,
> goto err_task;
> }
>
> + event->si_uattr = (unsigned long)attr_uptr;
> +
> if (is_sampling_event(event)) {
> if (event->pmu->capabilities & PERF_PMU_CAP_NO_INTERRUPT) {
> err = -EOPNOTSUPP;
