On 13.04.22 22:55, Mike Rapoport wrote:
> On Tue, Apr 12, 2022 at 02:05:51PM -0700, David Rientjes wrote:
>> On Tue, 12 Apr 2022, Andrew Morton wrote:
>>
>>> On Tue, 12 Apr 2022 13:16:23 -0700 Sudarshan Rajagopalan <quic_sudaraja@xxxxxxxxxxx> wrote:
>>>
>>>> Check if pfn is valid before or not before moving it to freelist.
>>>>
>>>> There are possible scenario where a pageblock can have partial physical
>>>> hole and partial part of System RAM. This happens when base address in RAM
>>>> partition table is not aligned to pageblock size.
>>>>
>>>> ...
>>>>
>>>>
>>>> Signed-off-by: Sudarshan Rajagopalan <quic_sudaraja@xxxxxxxxxxx>
>>>> Fixes: 4c7b9896621be ("mm: remove pfn_valid_within() and CONFIG_HOLES_IN_ZONE")
>>>
>>> I made that 859a85ddf90e714092dea71a0e54c7b9896621be and added
>>> cc:stable. I'll await reviewer input before proceeding further.
>>>
>>
>> Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
>>
>>>> --- a/mm/page_alloc.c
>>>> +++ b/mm/page_alloc.c
>>>> @@ -2521,6 +2521,11 @@ static int move_freepages(struct zone *zone,
>>>> int pages_moved = 0;
>>>>
>>>> for (pfn = start_pfn; pfn <= end_pfn;) {
>>>> + if (!pfn_valid(pfn)) {
>>>
>>> Readers will wonder how we can encounter an invalid pfn here. A small
>>> comment might help clue them in.
>>>
>>
>> Sudarshan can correct me if I'm wrong, but this has to do with the
>> pageblock alignment of the caller that assumes all pages in the range has
>> an underlying struct page that we can access but that fails to hold true
>> when we have a memory hole. A comment would definitely help:
>
> We do have a struct page for every page in a pageblock even if there is a
> hole in the physical memory. If this is not the case, there is more
> fundamental bug that should be fixed.
Also, I dislike handling such a corner case in a way that affects all
other sane cases. move_freepages() is also used for page isolation.
I agree that this should be fixed differently, if possible.
--
Thanks,
David / dhildenb
