assert "kd_lookup(kd->kd_unit) == NULL" failed in kcov.c

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 08948b0a81ee Avoid use after free when retrying the -o file
git tree: openbsd
console output: https://syzkaller.appspot.com/x/log.txt?x=14ad7607980000
kernel config: https://syzkaller.appspot.com/x/.config?x=1bc15e68cd2a49e5
dashboard link: https://syzkaller.appspot.com/bug?extid=884281bd3a80f838bdef

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2556c1dfe67b/disk-08948b0a.raw.xz
bsd.gdb: https://storage.googleapis.com/syzbot-assets/8c48872e6a31/bsd-08948b0a.gdb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e2f5c041fb3d/kernel-08948b0a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+884281...@syzkaller.appspotmail.com

panic: kernel diagnostic assertion "kd_lookup(kd->kd_unit) == NULL" failed: file "/syzkaller/managers/main/kernel/sys/dev/kcov.c", line 311
Starting stack trace...
panic(ffffffff830aeaa5) at panic+0x1ba sys/kern/subr_prf.c:229
__assert(ffffffff83068efa,ffffffff82fff96d,137,ffffffff8304d31e) at __assert+0x29
kcovopen(113d4,6,2000,ffff80002f9d7c10) at kcovopen+0x14f kd_lookup sys/dev/kcov.c:483 [inline]
kcovopen(113d4,6,2000,ffff80002f9d7c10) at kcovopen+0x14f sys/dev/kcov.c:311
spec_open_clone(ffff80003767b218) at spec_open_clone+0x287 sys/kern/spec_vnops.c:720
spec_open(ffff80003767b218) at spec_open+0x326 sys/kern/spec_vnops.c:148
VOP_OPEN(fffffd8058d45638,6,fffffd807f7d7750,ffff80002f9d7c10) at VOP_OPEN+0x82 sys/kern/vfs_vops.c:138
vn_open(ffff80003767b468,206,0) at vn_open+0x708 sys/kern/vfs_vnops.c:177
doopenat(ffff80002f9d7c10,ffffff9c,200000c0,205,0,ffff80003767b610) at doopenat+0x31d sys/kern/vfs_syscalls.c:1123
syscall(ffff80003767b6c0) at syscall+0x97e sys/arch/amd64/amd64/trap.c:577
Xsyscall() at Xsyscall+0x128
end of kernel
end trace frame: 0xe031aeaa670, count: 247
End of stack trace.


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