6cb40391c4
When HWPMC stops sampling, ps_pmc may be freed before samples are processed. In such situation treat PMC as stopped. Add "ifdef" to fix build without INVARIANTS code. Submitted by: Michal Mazur <mkm@semihalf.com> Obtained from: Semihalf Sponsored by: Stormshield, Netgate Differential revision: https://reviews.freebsd.org/D10912