[Bug 255208] FATAL crash/reboot upon trying to mount a VirtualBox shared folder in FreeBSD guest (13.0 RELEASE)

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=255208

Daniel Tameling <tamelingdaniel at gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |tamelingdaniel at gmail.com

--- Comment #3 from Daniel Tameling <tamelingdaniel at gmail.com> ---
I observed the same problem with a Windows 10 host. It works with 12.2 but
crashes consistently with 13.0. I managed to get a crash dump, and the panic is
caused by a page fault in kernel mode:

Fatal trap 12: page fault while in kernel mode
cpuid = 0; apic id = 00
fault virtual address   = 0x0
fault code              = supervisor read instruction, page not present
instruction pointer     = 0x20:0x0
stack pointer           = 0x0:0xfffffe009db5e688
frame pointer           = 0x0:0xfffffe009db5e6e0
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, long 1, def32 0, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 926 (mount_vboxvfs)
trap number             = 12
panic: page fault

The backtrace points to vn_lock:

#7  0xffffffff8108a83d in trap (frame=0xfffffe009db5e5c0)
    at /usr/src/sys/amd64/amd64/trap.c:398
#8  <signal handler called>
#9  0x0000000000000000 in ?? ()
#10 0xffffffff80cfc1b8 in VOP_LOCK1 (vp=0xfffff80070b687a0, flags=525312, 
    file=0xffffffff8299449d
"/wrkdirs/usr/ports/emulators/virtualbox-ose-additions/work/VirtualBox-6.1.18/src/VBox/Additions/freebsd/vboxvfs/vboxvfs_vnops.c",
line=252) at ./vnode_if.h:1127
#11 _vn_lock (vp=0xfffff80070b687a0, flags=525312, 
    file=0xffffffff8299449d
"/wrkdirs/usr/ports/emulators/virtualbox-ose-additions/work/VirtualBox-6.1.18/src/VBox/Additions/freebsd/vboxvfs/vboxvfs_vnops.c",
line=252) at /usr/src/sys/kern/vfs_vnops.c:1742

The corresponding code seems to be this:

/* Get a new vnode and associate it with our node. */
error = getnewvnode("vboxfs", mp, &vboxfs_vnodeops, &vp);
if (error != 0)
        goto unlock;
MPASS(vp != NULL);

/* lkflag is ignored, the lock is exclusive */
(void) vn_lock(vp, lkflag | LK_RETRY);

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