linux-kernel - Re: [PATCH v4 2/2] mm: Init page count in reserve_bootmem_region when MEMINIT

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Date:   Thu, 12 Oct 2023 17:36:40 +0800
From:   Yajun Deng <yajun.deng@...ux.dev>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     David Hildenbrand <david@...hat.com>, akpm@...ux-foundation.org,
        mike.kravetz@...cle.com, muchun.song@...ux.dev,
        willy@...radead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] mm: Init page count in reserve_bootmem_region when
 MEMINIT_EARLY


On 2023/10/12 17:19, Mike Rapoport wrote:
> On Thu, Oct 05, 2023 at 10:04:28PM +0800, Yajun Deng wrote:
>>>>>>>> That 'if' breaks the invariant that __free_pages_core is
>>>>>>>> always called for pages with initialized page count. Adding
>>>>>>>> it may lead to subtle bugs and random memory corruption so we
>>>>>>>> don't want to add it at the first place.
>>>>>>> As long as we have to special-case memory hotplug, we know that
>>>>>>> we are always coming via generic_online_page() in that case. We
>>>>>>> could either move some logic over there, or let
>>>>>>> __free_pages_core() know what it should do.
>>>>>> Looks like the patch rather special cases MEMINIT_EARLY, although
>>>>>> I didn't check throughfully other code paths.  Anyway, relying on
>>>>>> page_count() to be correct in different ways for different
>>>>>> callers of __free_pages_core() does not sound right to me.
>>>>> Absolutely agreed.
>>>>>
>>>> I already sent v5  a few days ago. Comments, please...
>>> Does it address all the feedback from this thread?
>> Except hotplug.
> Please reread carefully the last comments from me and from David above.
>

I replied in another thread about that 'if' statement. David just 
replied to me, let's discuss in another thread.