perf: weird si_code results on overflow signal

From: Vince Weaver
Date: Wed Sep 13 2017 - 12:01:00 EST


I just compiled up a fresh git kernel and all of the perf_event_test
overflow tests are failing.

The reason is that instead of getting POLL_IN or POLL_HUP sources as
expected, they are getting weird results in si_code of "-5".

I haven't had time to bisect this, but I do notice that some major changes
to si_code handling went in with