[5.6.0-rc2-next-20200218/powerpc] Boot failure on POWER9

[Michael Ellerman]

Sachin Sant <sachinp at linux.vnet.ibm.com> writes:
>> The patch below might work. Sachin can you test this? I tried faking up
>> a system with a memoryless node zero but couldn't get it to even start
>> booting.
>> 
> The patch did not help. The kernel crashed during
> the boot with the same call trace.
>
> BUG_ON() introduced with the patch was not triggered.

OK, that's weird.

I eventually managed to get a memoryless node going in sim, and it
appears to work there.

eg in dmesg:

  [    0.000000][    T0] numa:   NODE_DATA [mem 0x2000fffa2f80-0x2000fffa7fff]
  [    0.000000][    T0] numa:     NODE_DATA(0) on node 1
  [    0.000000][    T0] numa:   NODE_DATA [mem 0x2000fff9df00-0x2000fffa2f7f]
  ...
  [    0.000000][    T0] Early memory node ranges
  [    0.000000][    T0]   node   1: [mem 0x0000000000000000-0x00000000ffffffff]
  [    0.000000][    T0]   node   1: [mem 0x0000200000000000-0x00002000ffffffff]
  [    0.000000][    T0] Could not find start_pfn for node 0
  [    0.000000][    T0] Initmem setup node 0 [mem 0x0000000000000000-0x0000000000000000]
  [    0.000000][    T0] On node 0 totalpages: 0
  [    0.000000][    T0] Initmem setup node 1 [mem 0x0000000000000000-0x00002000ffffffff]
  [    0.000000][    T0] On node 1 totalpages: 131072
  
  # dmesg | grep set_numa
  [    0.000000][    T0] set_numa_mem: mem node for 0 = 1
  [    0.005654][    T0] set_numa_mem: mem node for 1 = 1

So is the problem more than just node zero having no memory?

cheers