panic() at panic+0x147
fifo_badop(ffffffff817c3e32) at fifo_badop+0x12
VOP_STRATEGY(ffffff0073c0e800) at VOP_STRATEGY+0x6b
bwrite(ffff800021141fd0) at bwrite+0x195
VOP_BWRITE(ffffff006bbd5968) at VOP_BWRITE+0x47
ufs_mkdir(ffffffff81e14008) at ufs_mkdir+0x5a9
VOP_MKDIR(ffff8000210c3780,1ed,ffffff9c,ffff800021141f88) at VOP_MKDIR+0x65
domkdirat(ffff8000211421c0,ffff8000210c3780,ffff8000210a5338,880) at domkdirat+0x10f
syscall(0) at syscall+0x3e4
Xsyscall(6,88,7f7ffffe9640,88,0,7f7ffffe9680) at Xsyscall+0x128
end of kernel
end trace frame: 0x7f7ffffe96b0, count: 4
https://www.openbsd.org/ddb.html describes the minimum info required in bug
reports.  Insufficient info makes it difficult to find and fix bugs.