linux-kernel - Re: [PATCH 2/2] mm/memory_hotplug: remove head page reference in scan_movable

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Message-ID: <Y87wdBlxBrYjzADJ@casper.infradead.org>
Date:   Mon, 23 Jan 2023 20:39:16 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Sidhartha Kumar <sidhartha.kumar@...cle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, david@...hat.com, osalvador@...e.de
Subject: Re: [PATCH 2/2] mm/memory_hotplug: remove head page reference in
 scan_movable_pages()

On Mon, Jan 23, 2023 at 12:23:47PM -0800, Sidhartha Kumar wrote:
> -		if (!PageHuge(page))
> +		folio = page_folio(page);
> +		if (!folio_test_hugetlb(folio))
>  			continue;
> -		head = compound_head(page);
>  		/*
>  		 * This test is racy as we hold no reference or lock.  The
>  		 * hugetlb page could have been free'ed and head is no longer

Assuming the comment is correct, this patch is also unsafe.