linux-kernel - Re: [PATCH 2/2] mm,memory_hotplug: {READ,WRITE}

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Message-ID: <Zk39BD7NPbP7WJOz@google.com>
Date: Wed, 22 May 2024 14:11:16 +0000
From: Brendan Jackman <jackmanb@...gle.com>
To: David Hildenbrand <david@...hat.com>
Cc: Oscar Salvador <osalvador@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Rapoport <rppt@...nel.org>, Michal Hocko <mhocko@...e.com>,
	Anshuman Khandual <anshuman.khandual@....com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Pavel Tatashin <pasha.tatashin@...een.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm,memory_hotplug: {READ,WRITE}_ONCE unsynchronized
 zone data

On Wed, May 22, 2024 at 04:05:12PM +0200, David Hildenbrand wrote:
> On 21.05.24 14:57, Brendan Jackman wrote:
> > +	return zone->zone_start_pfn + READ_ONCE(zone->spanned_pages);
> 
> It's weird to apply that logic only to spanned_pages, whereby zone_start_pfn
> can (and will) similarly change when onlining/offlining memory.
> 
Oh, yep. For some reason I had decided that zone_start_pfn was fixed
but that is (actually very obviously) not true!

Will take a closer look and extend v2 to cover that too, unless
someone finds a reason this whole patch is nonsense.

Thanks for the review.