On 2025/2/13 2:28, Catalin Marinas wrote:
@@ -1339,9 +1349,27 @@ int arch_add_memory(int nid, u64 start, u64 size,
struct mhp_params *params)
{
int ret, flags = NO_EXEC_MAPPINGS;
+ unsigned long start_pfn = PFN_DOWN(start);
+ struct mem_section *ms = __pfn_to_section(start_pfn);
VM_BUG_ON(!mhp_range_allowed(start, size, true));
+ /* should not be invoked by early section */
+ WARN_ON(early_section(ms));
I don't remember the discussion, do we still need this warning here if
the sections are not marked as early? I guess we can keep it if one does
an arch_add_memory() on an early section.
I think I suggested to use a WARN_ON_ONCE(!present_section()) but I
completely forgot the memory hotplug code paths.
Dear Catalin,
The previous discussion can be found at
https://lore.kernel.org/lkml/aedbbc4f-8f6c-46d8-a8d7-53103675a816@xxxxxxxxxxx/,
I highlighted the key points from conversation between me and Anshuman
for your reference:
"
>>
>> BTW, shall we remove the check for !early_section since
arch_add_memory is only called during hotplugging case? Correct me
please if I'm mistaken :)
>
> While this is true, still might be a good idea to keep the
early_section()
> check in place just to be extra careful here. Otherwise an WARN_ON()
might
> be needed.
Make sense. I would like to add some comments and WARN_ON() if
early_section().
"
Regarding your suggestion, I believed it was intended for the
vmemmap_populate() function ?(Discussion:
https://lore.kernel.org/linux-mm/Z3_d59kp4CuHQp97@xxxxxxx/), but as
workflow below indicates:
Hot plug:
1. section_activate -> vmemmap_populate
2. mark PRESENT
In contrast, the early flow:
1. memblocks_present -> mark PRESENT
2. __populate_section_memmap -> vmemmap_populate
Could this result in a false warning during hotplugging? I replied with
the doubt in above link before but seems you missed :) Could you please
share your thoughts if you have a different idea ?
I will include your tags, correct capitalization nit and post one new
version.
