diff options
| author | Andre Silva <andasilv@amd.com> | 2026-08-11 16:16:20 +0000 |
|---|---|---|
| committer | Mitchell Horne <mhorne@FreeBSD.org> | 2026-08-11 16:22:01 +0000 |
| commit | 66118c3f1011d7852bce8b659899179a83781897 (patch) | |
| tree | 8597490574842d133e891b4b9bae6ea1cdc9d972 | |
| parent | e85ae6f6a6c0574fdad92b986e37f04f20d5135f (diff) | |
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 <andasilv@amd.com>
Reviewed by: mhorne
MFC after: 1 week
Sponsored by: AMD
Differential Revision: https://reviews.freebsd.org/D58571
| -rw-r--r-- | sys/dev/hwpmc/hwpmc_mod.c | 7 |
1 files 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 |