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

[Vlastimil Babka]

On 3/13/20 12:12 PM, Srikar Dronamraju wrote:
> * Michael Ellerman <mpe at ellerman.id.au> [2020-03-13 21:48:06]:
> 
>> 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?
>> 
> 
> The problem would happen with possible nodes which are not yet present. i.e
> no cpus, no memory attached to those nodes.
> 
> Please look at
> http://lore.kernel.org/lkml/20200312131438.GB3277@linux.vnet.ibm.com/t/#u
> for more details.
> 
> The summary being: pgdat/Node_Data for such nodes is not allocated. Hence

Michael's log shows that his pgdat is still allocated. But perhaps Sachin had
also your 3 patches from the other thread applied, in addition to Michael's
patch. So in his case pgdat for node 0 would indeed be no longer allocated, and
thus SLUB code was crashing in node_present_pages() instead.

> the node_present_pages(nid) called  where nid is a possible but not yet
> present node fails. Currently node_present_pages(nid) and node_to_mem_node
> don't seem to be equipped to handle possible but not present nodes.
> 
>> cheers
>