siginfo pid not populated from ptrace?

[Tycho Andersen]

Hi Oleg,

I've been running some tests on my seccomp series, and in one of the
tests on v4.20-rc2, I noticed,

[ RUN      ] global.syscall_restart
seccomp_bpf.c:2784:global.syscall_restart:Expected getpid() (1492) == info._sifields._kill.si_pid (0)
global.syscall_restart: Test failed at step #22

which seems unrelated to my series (the kernel was stock v4.20 with my
patches on top).

I've been running a lot of tests, and only seen this once, so it seems
like a fairly rare race. I tried to look through the code but didn't
see anything obvious. Thoughts?

Tycho