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 12:19:06 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Yajun Deng <yajun.deng@...ux.dev>
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 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.

-- 
Sincerely yours,
Mike.