=== DF-2442 panic signature (from serial console) ===
=== Trigger: 8 concurrent create('df2442race') ioctls, round 1 ===
=== Root cause: dm_dev_insert:195 KKASSERT(dmv != NULL) — TOCTOU race ===

panic: assertion "dmv != NULL" failed in dm_dev_insert at /usr/src/sys/dev/disk/dm/dm_dev.c:195
cpuid = 3
Trace beginning at frame 0xfffff80118497208
dm_dev_insert() at dm_dev_insert+0xe1 0xffffffff82600fe1 
dm_dev_create() at dm_dev_create+0x223 0xffffffff82601283 
dm_dev_create_ioctl() at dm_dev_create_ioctl+0xa0 0xffffffff82601930 
dmioctl() at dmioctl+0x2eb 0xffffffff8260083b 
dev_dioctl() at dev_dioctl+0x65 0xffffffff8062cdb5 
Debugger("panic")

CPU3 stopping CPUs: 0x00000037
 stopped
Stopped at      Debugger+0x7c:  movb    $0,0xbdaf09(%rip)
db>