# guest run (stock kernel #0, after DF-3106 fix-validation reset):
#   sh /root/df3107/stress.sh   (renames on vn-backed UFS mount /mnt/cp; churn on /tmp)
hierarchy ready; starting stress 11:00:09   [first attempt: $SECONDS unsupported by guest sh - loops rewrote to counters]
--- second attempt (counters) ---
renames completed: 20000 (mv errors: 0)
churn iterations: 60000
STRESS_DONE 11:04:15; dmesg tail:
HAMMER2: VOLDATA DUMP
HAMMER2: INITIATE SPANs
swap low/high-water marks set to 41940/62910
vn4/vn5: MBR magic not found (vn noise only)
=> no crash, no anomalous dmesg, guest up. Zero-ref use happens on every
   rename (code-path certain); the vnode-recycle race window (a few
   instructions between vput(vp) at :1160 and the vp->v_mount read at
   :1161) was not won in 20,000 attempts.