On Wed, Jul 22, 2020 at 11:42:08AM -0700, Song Liu wrote:
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 856d98c36f562..f77d009fcce95 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -9544,6 +9544,24 @@ static int perf_event_set_bpf_handler(struct perf_event *event, u32 prog_fd)
> if (IS_ERR(prog))
> return PTR_ERR(prog);
>
> + if (event->attr.precise_ip &&
> + prog->call_get_stack &&
> + (!(event->attr.sample_type & __PERF_SAMPLE_CALLCHAIN_EARLY) ||
> + event->attr.exclude_callchain_kernel ||
> + event->attr.exclude_callchain_user)) {
> + /*
> + * On perf_event with precise_ip, calling bpf_get_stack()
> + * may trigger unwinder warnings and occasional crashes.
> + * bpf_get_[stack|stackid] works around this issue by using
> + * callchain attached to perf_sample_data. If the
> + * perf_event does not full (kernel and user) callchain
> + * attached to perf_sample_data, do not allow attaching BPF
> + * program that calls bpf_get_[stack|stackid].
> + */
> + bpf_prog_put(prog);
> + return -EINVAL;
I suspect this will be a common error. bpftrace and others will be hitting
this issue and would need to fix how they do perf_event_open.
But EINVAL is too ambiguous and sys_perf_event_open has no ability to
return a string.
So how about we pick some different errno here to make future debugging
a bit less painful?
May be EBADFD or EPROTO or EPROTOTYPE ?
I think anything would be better than EINVAL.
