DF-2606 fix-validation rw stress (stock kernel froze in DDB on this exact input; fixed kernel):
--- command: /root/df2606/stress-fix.sh (vn2=h2.img patched keybits=65, rw mount, 60 creates)
MOUNT_OK (rw)
LOOP_DONE
SYNC_DONE
entries now:       85
--- kernel messages (fubar/bad bref/CHECK FAIL/panic):
--- nothing above means clean handling
UMOUNT_OK
GUEST_STILL_ALIVE

--- post-check:
GUEST_ALIVE
 2:26AM  up 3 mins, 0 users, load averages: 0.02, 0.03, 0.01