[*] DF-2437 dm_target_delay objcache-destroy-on-unload
[*] loaded modules:
 4    2 0xffffffff82600000    a2000 dm.ko
 5    1 0xffffffff826a2000    19000 dm_target_delay.ko

[*] step 1: create + reload + resume delay device
[*] DF-2437 setup: create + reload + resume delay device
[*] delay device 'df2437' is now ACTIVE with 100ms delay
[*] device accessible at /dev/mapper/df2437

[*] step 2: starting background I/O on delay device
[*] step 3: kldunload dm_target_delay (destroys objcache despite EBUSY)
(SSH HANGS -- guest panicked)

PANIC (from boot.log):
Fatal user address access from kernel mode from dd at ffffffff8064b175
Fatal trap 12: page fault while in kernel mode
cpuid = 2; Stopped at      objcache_put+0x3a:      addq    $0x1,0xa8(%r12)
db>