Re: [PATCH 1/2] arm64: avoid alloc memory on offline node

[Xie XiuQi]

Hi Michal,

On 2018/6/11 16:52, Michal Hocko wrote:
> On Mon 11-06-18 11:23:18, Xie XiuQi wrote:
>> Hi Michal,
>>
>> On 2018/6/7 20:21, Michal Hocko wrote:
>>> On Thu 07-06-18 19:55:53, Hanjun Guo wrote:
>>>> On 2018/6/7 18:55, Michal Hocko wrote:
>>> [...]
>>>>> I am not sure I have the full context but pci_acpi_scan_root calls
>>>>> kzalloc_node(sizeof(*info), GFP_KERNEL, node)
>>>>> and that should fall back to whatever node that is online. Offline node
>>>>> shouldn't keep any pages behind. So there must be something else going
>>>>> on here and the patch is not the right way to handle it. What does
>>>>> faddr2line __alloc_pages_nodemask+0xf0 tells on this kernel?
>>>>
>>>> The whole context is:
>>>>
>>>> The system is booted with a NUMA node has no memory attaching to it
>>>> (memory-less NUMA node), also with NR_CPUS less than CPUs presented
>>>> in MADT, so CPUs on this memory-less node are not brought up, and
>>>> this NUMA node will not be online (but SRAT presents this NUMA node);
>>>>
>>>> Devices attaching to this NUMA node such as PCI host bridge still
>>>> return the valid NUMA node via _PXM, but actually that valid NUMA node
>>>> is not online which lead to this issue.
>>>
>>> But we should have other numa nodes on the zonelists so the allocator
>>> should fall back to other node. If the zonelist is not intiailized
>>> properly, though, then this can indeed show up as a problem. Knowing
>>> which exact place has blown up would help get a better picture...
>>>
>>
>> I specific a non-exist node to allocate memory using kzalloc_node,
>> and got this following error message.
>>
>> And I found out there is just a VM_WARN, but it does not prevent the memory
>> allocation continue.
>>
>> This nid would be use to access NODE_DADA(nid), so if nid is invalid,
>> it would cause oops here.
>>
>> 459 /*
>> 460  * Allocate pages, preferring the node given as nid. The node must be valid and
>> 461  * online. For more general interface, see alloc_pages_node().
>> 462  */
>> 463 static inline struct page *
>> 464 __alloc_pages_node(int nid, gfp_t gfp_mask, unsigned int order)
>> 465 {
>> 466         VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES);
>> 467         VM_WARN_ON(!node_online(nid));
>> 468
>> 469         return __alloc_pages(gfp_mask, order, nid);
>> 470 }
>> 471
>>
>> (I wrote a ko, to allocate memory on a non-exist node using kzalloc_node().)
> 
> OK, so this is an artificialy broken code, right. You shouldn't get a
> non-existent node via standard APIs AFAICS. The original report was
> about an existing node which is offline AFAIU. That would be a different
> case. If I am missing something and there are legitimate users that try
> to allocate from non-existing nodes then we should handle that in
> node_zonelist.

I think hanjun's comments may help to understood this question:
 - NUMA node will be built if CPUs and (or) memory are valid on this NUMA node;

 - But if we boot the system with memory-less node and also with CONFIG_NR_CPUS
   less than CPUs in SRAT, for example, 64 CPUs total with 4 NUMA nodes, 16 CPUs
   on each NUMA node, if we boot with CONFIG_NR_CPUS=48, then we will not built
   numa node for node 3, but with devices on that numa node, alloc memory will
   be panic because NUMA node 3 is not a valid node.

I triggered this BUG on arm64 platform, and I found a similar bug has been fixed
on x86 platform. So I sent a similar patch for this bug.

Or, could we consider to fix it in the mm subsystem?