perf: perf_fuzzer quickly locks up on 4.15-rc7

[Vince Weaver]

Hello

Was trying out current git (4.15-rc7) and the perf_fuzzer very quickly 
will lock up my Haswell test machine so solidly that I don't get any debug 
info, even with a serial console.

I'll try enabling various debug options to see if I can get a more useful 
bug report.

Vince