The branch main has been updated by mhorne: URL: https://cgit.FreeBSD.org/src/commit/?id=66118c3f1011d7852bce8b659899179a83781897
commit 66118c3f1011d7852bce8b659899179a83781897 Author: Andre Silva <[email protected]> AuthorDate: 2026-08-11 16:16:20 +0000 Commit: Mitchell Horne <[email protected]> CommitDate: 2026-08-11 16:22:01 +0000 hwpmc: fix false runcount assertion in user callchain capture pmc_capture_user_callchain() checks a PMC's runcount before walking the user stack, but reads it without holding the spinlock that protects it. hardclock() can run on the same CPU during the capture and drop the runcount to zero in between, tripping the assertion and panicking INVARIANTS kernels under load. Move the check inside the existing spinlock, right where the code already confirms the sample is still valid. No functional change on kernels built without INVARIANTS. Signed-off-by: Andre Silva <[email protected]> Reviewed by: mhorne MFC after: 1 week Sponsored by: AMD Differential Revision: https://reviews.freebsd.org/D58571 --- sys/dev/hwpmc/hwpmc_mod.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/sys/dev/hwpmc/hwpmc_mod.c b/sys/dev/hwpmc/hwpmc_mod.c index 32bb00d671fe..e2d5a044e0b8 100644 --- a/sys/dev/hwpmc/hwpmc_mod.c +++ b/sys/dev/hwpmc/hwpmc_mod.c @@ -5016,9 +5016,6 @@ restart: KASSERT(pm->pm_flags & PMC_F_CALLCHAIN, ("[pmc,%d] Retrieving callchain for PMC that doesn't " "want it", __LINE__)); - KASSERT(counter_u64_fetch(pm->pm_runcount) > 0, - ("[pmc,%d] runcount %ju", __LINE__, - (uintmax_t)counter_u64_fetch(pm->pm_runcount))); if (ring == PMC_UR) { counter_u64_add(pmc_stats.pm_merges, 1); @@ -5044,6 +5041,10 @@ restart: * Verify that the sample hasn't been dropped in the meantime. */ if (ps->ps_nsamples == PMC_USER_CALLCHAIN_PENDING) { + KASSERT(counter_u64_fetch(pm->pm_runcount) > 0, + ("[pmc,%d] runcount %ju", __LINE__, + (uintmax_t)counter_u64_fetch(pm->pm_runcount))); + ps->ps_nsamples = nsamples; /* * If we couldn't get a sample, simply drop the
