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

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Message-ID: <20231005050619.GB3303@kernel.org>
Date:   Thu, 5 Oct 2023 08:06:19 +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 Tue, Oct 03, 2023 at 10:38:09PM +0800, Yajun Deng wrote:
> 
> On 2023/10/2 19:25, David Hildenbrand wrote:
> > On 02.10.23 13:10, Mike Rapoport 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?

-- 
Sincerely yours,
Mike.