> On Jul 22, 2020, at 10:55 PM, Alexei Starovoitov
> <[email protected]> wrote:
>
> 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.
I like EPROTO most. I will change it to EPROTO if we don't have better ideas.
Btw, this is not the error code on sys_perf_event_open(). It is the ioctl()
on the perf_event fd. So debugging this error will be less painful than
debugging sys_perf_event_open() errors.
Thanks,
Song
