uvm_fault(0xffffffff83ae5038, 0xffff800026c72008, 0, 1) -> d
kernel: page fault trap, code=0
Stopped at      ffs2_balloc+0xa0a:      movq    0(%rcx,%rax,8),%r14
    TID    PID    UID     PRFLAGS     PFLAGS  CPU  COMMAND
*450073  38428      0           0  0x4000000    0  syz-executor
ffs2_balloc(fffff8806f55fb00,35949,1,fffff88007ffd820,3,ffff8000380d7448) at ffs2_balloc+0xa0a sys/ufs/ffs/ffs_balloc.c:614
ffs_write(ffff8000380d74d0) at ffs_write+0x4f9 sys/ufs/ffs/ffs_vnops.c:345
VOP_WRITE(fffff8806d9a5888,ffff8000380d7688,7,fffff88007ffd820) at VOP_WRITE+0x101 sys/kern/vfs_vops.c:245
vn_write(fffff8806f89e9e0,ffff8000380d7688,0) at vn_write+0x1c2 sys/kern/vfs_vnops.c:414
dofilewritev(ffff80002a76bca0,4,ffff8000380d7688,0,ffff8000380d7730) at dofilewritev+0x2bd sys/kern/sys_generic.c:384
sys_write(ffff80002a76bca0,ffff8000380d77e0,ffff8000380d7730) at sys_write+0xa2 sys/kern/sys_generic.c:300
syscall(ffff8000380d77e0) at syscall+0x962 mi_syscall sys/sys/syscall_mi.h:-1 [inline]
syscall(ffff8000380d77e0) at syscall+0x962 sys/arch/amd64/amd64/trap.c:783
Xsyscall() at Xsyscall+0x128
end of kernel
end trace frame: 0xe4f9cfbcc90, count: 7
https://www.openbsd.org/ddb.html describes the minimum info required in bug
reports.  Insufficient info makes it difficult to find and fix bugs.
ddb> 
ddb> set $lines = 0
ddb> set $maxwidth = 0
ddb> show panic
*cpu0: uvm_fault(0xffffffff83ae5038, 0xffff800026c72008, 0, 1) -> d
ddb> show kasan
No such command
ddb> trace
ffs2_balloc(fffff8806f55fb00,35949,1,fffff88007ffd820,3,ffff8000380d7448) at ffs2_balloc+0xa0a sys/ufs/ffs/ffs_balloc.c:614
ffs_write(ffff8000380d74d0) at ffs_write+0x4f9 sys/ufs/ffs/ffs_vnops.c:345
VOP_WRITE(fffff8806d9a5888,ffff8000380d7688,7,fffff88007ffd820) at VOP_WRITE+0x101 sys/kern/vfs_vops.c:245
vn_write(fffff8806f89e9e0,ffff8000380d7688,0) at vn_write+0x1c2 sys/kern/vfs_vnops.c:414
dofilewritev(ffff80002a76bca0,4,ffff8000380d7688,0,ffff8000380d7730) at dofilewritev+0x2bd sys/kern/sys_generic.c:384
sys_write(ffff80002a76bca0,ffff8000380d77e0,ffff8000380d7730) at sys_write+0xa2 sys/kern/sys_generic.c:300
syscall(ffff8000380d77e0) at syscall+0x962 mi_syscall sys/sys/syscall_mi.h:-1 [inline]
syscall(ffff8000380d77e0) at syscall+0x962 sys/arch/amd64/amd64/trap.c:783
Xsyscall() at Xsyscall+0x128
end of kernel
end trace frame: 0xe4f9cfbcc90, count: -8
ddb> show registers
rdi                                0
rsi                              0x2
rbp               0xffff8000380d73f0
rbx               0xfffff8806f55fb00
rdx                                0
rcx               0xffff800026c72000
rax                              0x1
r8                0xffffffffffffffff
r9                0xffff8000380d7448
r10                                0
r11               0x43fce4d4c5d93da6
r12                              0x1
r13               0xffff800000c48800
r14               0xffff8000380d7290
r15               0xfffff8806378c120
rip               0xffffffff8264102a    ffs2_balloc+0xa0a
cs                               0x8
rflags                       0x10246    __ALIGN_SIZE+0xf246
rsp               0xffff8000380d7280
ss                              0x10
ffs2_balloc+0xa0a:      movq    0(%rcx,%rax,8),%r14
ddb> show proc
PROC (syz-executor) tid=450073 pid=38428 tcnt=2 stat=onproc
    flags process=0 proc=4000000<THREAD>
    runpri=32, usrpri=50, slppri=32, nice=20
    wchan=0x0, wmesg=, ps_single=0x0 scnt=0 ecnt=0
    forw=0xffffffffffffffff, list=0xffff80002a76b770,0xffff80002a778020
    process=0xffff8000380d8918 user=0xffff8000380d2000, vmspace=0xfffff8807f229450
    estcpu=36, cpticks=1, pctcpu=0.0, user=0, sys=1, intr=0
ddb>