[Bug 267028] kernel panics when booting with both (zfs,ko or vboxnetflt,ko or acpi_wmi.ko) and amdgpu.ko

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=267028

--- Comment #85 from George Mitchell <george@m5p.com> ---
I have a new crash, but I did not get a dump because of an issue I will explain
below.

For those who came in late, here's a summary of my system.  dmesg says I
have:CPU: AMD Ryzen 3 2200G with Radeon Vega Graphics     (3493.71-MHz K8-class
CPU)
  Origin="AuthenticAMD"  Id=0x810f10  Family=0x17  Model=0x11  Stepping=0
 
Features=0x178bfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,MMX,FXSR,SSE,SSE2,HTT>
 
Features2=0x7ed8320b<SSE3,PCLMULQDQ,MON,SSSE3,FMA,CX16,SSE4.1,SSE4.2,MOVBE,POPCNT,AESNI,XSAVE,OSXSAVE,AVX,F16C,RDRAND>
  AMD Features=0x2e500800<SYSCALL,NX,MMX+,FFXSR,Page1GB,RDTSCP,LM>
  AMD
Features2=0x35c233ff<LAHF,CMP,SVM,ExtAPIC,CR8,ABM,SSE4A,MAS,Prefetch,OSVW,SKINIT,WDT,TCE,Topology,PCXC,PNXC,DBE,PL2I,MWAITX>
  Structured Extended
Features=0x209c01a9<FSGSBASE,BMI1,AVX2,SMEP,BMI2,RDSEED,ADX,SMAP,CLFLUSHOPT,SHA>
  XSAVE Features=0xf<XSAVEOPT,XSAVEC,XINUSE,XSAVES>
  AMD Extended Feature Extensions ID EBX=0x1007<CLZERO,IRPerf,XSaveErPtr,IBPB>
  SVM: NP,NRIP,VClean,AFlush,DAssist,NAsids=32768
  TSC: P-state invariant, performance statistics

My motherboard is a Gigabyte B450M D53H.
BIOS is American Megatrends version F4, dated 1/25/2019.

pciconf -lv says:
vgapci0@pci0:6:0:0:     class=0x030000 rev=0xc8 hdr=0x00 vendor=0x1002
device=0x15dd subvendor=0x1458 subdevice=0xd000
    vendor     = 'Advanced Micro Devices, Inc. [AMD/ATI]'
    device     = 'Raven Ridge [Radeon Vega Series / Radeon Vega Mobile Series]'
    class      = display
    subclass   = VGA

Until recently, when I was running FBSD 12-RELEASE, my box had one hard drive. 
I added a new drive when I upgraded to FBSD 13-RELEASE so I would still have
FBSD 12 as an emergency backup.  Part of the upgrade is that on the new disk I
created a small UFS slice for /, /var, and /tmp, and most of the rest of the
disk is a ZFS slice for /usr (so I wouldn't have to wait for fsck on reboot
after crashes).  That means that it isn't practical to do a test without ZFS on
that new disk (I'll call it my regular disk now).  So I installed FBSD 13 (same
version as my regular disk) on the old disk (I'll call it the test disk now),
which had (and still has) a small UFS slice for /, /var, and /tmp and a big UFS
slice for /usr.

To boot from the test disk, I use the BIOS boot menu, since (unsurprisingly) I
have set the default boot disk to my regular disk.

I removed all mentions of ZFS and VBOX from /boot/loader.conf and /etc/rc.conf
on the test disk.  Then I booted up a whole bunch of times.  On the thirteenth
try, I got the crash.  Unfortunately, I don't have a crash summary from it
because the system rebooted from my regular disk instead of the test disk while
I was still staring at the crash message on the screen.  Subsequently, I booted
20 more times from the test disk without getting the crash again.

What I saw (for a few seconds) on the screen from the one crash sure looked
like the same old backtrace, and I have to say, to an ignorant yokel like
myself, it seemed to be saying that there's a locking problem in amdgpu.  There
was absolutely no virtual terminal switching, because I had not started an X
server and I did not type ALT+Fn.

I'll try getting a proper crash dump later (possibly tomorrow).  My thanks to
all of you for your patience.

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