Comment 20 for bug 1773162

With `loglevel=7 initcall_debug nosplash` on the command line I got a little further, I believe.

```
[…]
[ 0.000000] Linux version 4.15.0-22-generic (buildd@bos02-ppc64el-009) (gcc version 7.3.0 (Ubuntu 7.3.0-16ubuntu3)) #24-Ubuntu SMP Wed May 16 12:12:37 UTC 2018 (Ubuntu 4.15.0-22.24-generic 4.15.17)
[…]
[ 0.000000] Kernel command line: root=UUID=2c3dd738-785a-469b-843e-9f0ba8b47b0d ro rootflags=subvol=@ loglevel=7 initcall_debug nosplash
[…]
[ 3.290595] Bad kernel stack pointer 7fffc010e3d0 at c00000000000b9ec
[ 3.290639] Oops: Bad kernel stack pointer, sig: 6 [#1]
[ 3.290671] LE SMP NR_CPUS=2048 NUMA PowerNV
[ 3.290705] Modules linked in:
[ 3.290731] CPU: 56 PID: 1200 Comm: modprobe Not tainted 4.15.0-22-generic #24-Ubuntu
[ 3.290778] NIP: c00000000000b9ec LR: 0000000000000000 CTR: 0000000000000000
[ 3.290826] REGS: c00000003fd5fd40 TRAP: 0300 Not tainted (4.15.0-22-generic)
[ 3.290872] MSR: 9000000000001031 <SF,HV,ME,IR,DR,LE> CR: 00000000 XER: 00000000
[ 3.290922] CFAR: c00000000000b934 DAR: 000000000002b200 DSISR: 40000000 SOFTE: -4611686018403131680
[ 3.290922] GPR00: 0000000000000000 00007fffc010e3d0 0000000000000000 0000000000000000
[ 3.290922] GPR04: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 3.290922] GPR08: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 3.290922] GPR12: 000074c38e101700 000000000002b200 0000000000000000 0000000000000000
[ 3.290922] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 3.290922] GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 3.290922] GPR24: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 3.290922] GPR28: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 3.291350] NIP [c00000000000b9ec] fast_exception_return+0x9c/0x184
[ 3.291389] LR [0000000000000000] (null)
[ 3.291419] Call Trace:
[ 3.291435] Instruction dump:
[ 3.291460] e84101a0 7c4ff120 e8410170 7c5a03a6 e8010070 e8410080 e8610088 e8810090
[ 3.291509] e8210078 7db243a6 7db142a6 7c0004ac <e9ad0000> 63ff0000 7db242a6 63ff0000
[ 3.291560] ---[ end trace 12eb35aa3ef49d58 ]---
```

Please find the full log attached.