syncing disks...panic: kernel diagnostic assertion "vp->v_usecount == 0" failed: file "/syzkaller/managers/setuid/kernel/sys/kern/vfs_subr.c", line 639
Stopped at      db_enter+0x25:  addq    $0x8,%rsp
    TID    PID    UID     PRFLAGS     PFLAGS  CPU  COMMAND
*464474      1      0   0x8000002          0    0K init
db_enter() at db_enter+0x25 sys/arch/amd64/amd64/db_interface.c:437
panic(ffffffff830d8f7b) at panic+0x1e5 sys/kern/subr_prf.c:198
__assert(ffffffff8308c773,ffffffff8304144b,27f,ffffffff8302787c) at __assert+0x29
vdoom(fffffd806c8702e8) at vdoom+0x105 sys/kern/vfs_subr.c:641
ufs_inactive(ffff800029f89bd8) at ufs_inactive+0x188 sys/ufs/ufs/ufs_inode.c:89
VOP_INACTIVE(fffffd806c8702e8,ffff8000fffffbd8) at VOP_INACTIVE+0x107 sys/kern/vfs_vops.c:495
vclean(fffffd806c8702e8,8,ffff8000fffffbd8) at vclean+0x234 sys/kern/vfs_subr.c:1107
vgonel(fffffd806c8702e8,ffff8000fffffbd8) at vgonel+0xec sys/kern/vfs_subr.c:1197
vflush_vnode(fffffd806c8702e8,ffff800029f89d50) at vflush_vnode+0x2e5 sys/kern/vfs_subr.c:1011
vflush(ffff800000a66c00,0,2) at vflush+0x72 sys/kern/vfs_subr.c:1021
ffs_flushfiles(ffff800000a66c00,2,ffff8000fffffbd8) at ffs_flushfiles+0x80 sys/ufs/ffs/ffs_vfsops.c:985
ffs_unmount(ffff800000a66c00,80000,ffff8000fffffbd8) at ffs_unmount+0x5a sys/ufs/ffs/ffs_vfsops.c:928
dounmount_leaf(ffff800000a66c00,80000,ffff8000fffffbd8) at dounmount_leaf+0x18d sys/kern/vfs_syscalls.c:496
dounmount(ffff800000a66c00,80000,ffff8000fffffbd8) at dounmount+0x20f
end trace frame: 0xffff800029f89f90, count: 0
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{0}> 
ddb{0}> set $lines = 0
ddb{0}> set $maxwidth = 0
ddb{0}> show panic
*cpu0: kernel diagnostic assertion "vp->v_usecount == 0" failed: file "/syzkaller/managers/setuid/kernel/sys/kern/vfs_subr.c", line 639
ddb{0}>