linux-kernel - Re: [PATCH v6 03/10] mm,memory_hotplug: Implement numa node notifier

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Message-ID: <aFADwYs9LcyK5tVn@localhost.localdomain>
Date: Mon, 16 Jun 2025 13:45:05 +0200
From: Oscar Salvador <osalvador@...e.de>
To: David Hildenbrand <david@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Harry Yoo <harry.yoo@...cle.com>, Rakie Kim <rakie.kim@...com>,
	Hyeonggon Yoo <42.hyeyoo@...il.com>,
	Joshua Hahn <joshua.hahnjy@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 03/10] mm,memory_hotplug: Implement numa node notifier

On Mon, Jun 16, 2025 at 10:52:31AM +0200, David Hildenbrand wrote:
> Probably worth checking, to make sure we don't have accidental bugs in there
> ...

I did a quick sweep, and we should be cool since users of the node notifier
don't really use *_CANCEL* action. Only ADDED/REMOVED.

Now, users of memory notifier is a different story.
E.g: page_ext will call offline_page_ext to mark the section->page_ext invalid.

online_page_ext does:

 base = alloc_page_ext(table_size, nid);
 section->page_ext = (void *)base - page_ext_size * pfn;

This is fine, I think, offline_page_ext will not mark it as INVALID because
section->page_ext is NULL, so we just skip it.

This is just one example. I checked some others like kasan and hyperv and they
seem fine.
And anyway, the we could already hit this situation with MEM_* notifiers, so
nothing new.
I'll just make sure to document it so new users take this into account.

-- 
Oscar Salvador
SUSE Labs