From: Matthew Wilcox <willy@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: mm-commits@vger.kernel.org, vbabka@kernel.org, surenb@google.com,
stable@vger.kernel.org, sourabhjain@linux.ibm.com,
rppt@kernel.org, ritesh.list@gmail.com, mhocko@suse.com,
luizcap@redhat.com, ljs@kernel.org, liam@infradead.org,
david@kernel.org, aboorvad@linux.ibm.com
Subject: Re: + mm-util-dont-read-__page_2-for-order-1-folios-in-snapshot_page.patch added to mm-hotfixes-unstable branch
Date: Wed, 8 Jul 2026 23:06:42 +0100 [thread overview]
Message-ID: <ak7J8oaLkNsWNOrx@casper.infradead.org> (raw)
In-Reply-To: <20260708205653.14D251F000E9@smtp.kernel.org>
On Wed, Jul 08, 2026 at 01:56:52PM -0700, Andrew Morton wrote:
> From: Aboorva Devarajan <aboorvad@linux.ibm.com>
> Subject: mm/util: don't read __page_2 for order-1 folios in snapshot_page()
> Date: Thu, 9 Jul 2026 01:49:54 +0530
>
> snapshot_page() currently reads __page_2 after checking nr_pages > 1, but
> it should only do so when nr_pages > 2.
>
> If an order-1 folio is allocated at the end of a vmemmap section,
> __page_2 will not exist and reading it will cause a fault.
>
> During DLPAR memory remove on a 22 TB ppc64le LPAR, snapshot_page() oopsed
> on the page isolation path while reading an order-1 folio's __page_2 from
> an adjacent absent section (unmapped vmemmap).
>
> Fix this to avoid reading memmap that doesn't exist (e.g., a vmemmap
> hole).
>
> Link: https://lore.kernel.org/20260708201954.686111-1-aboorvad@linux.ibm.com
> Fixes: 31a31da8a618 ("mm: move _pincount in folio to page[2] on 32bit")
> Signed-off-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
> Reported-by: Sourabh Jain <sourabhjain@linux.ibm.com>
> Acked-by: David Hildenbrand (Arm) <david@kernel.org>
> Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
You're taking my R-b without taking my rewording of the second
paragraph?
next prev parent reply other threads:[~2026-07-08 22:06 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-08 20:56 + mm-util-dont-read-__page_2-for-order-1-folios-in-snapshot_page.patch added to mm-hotfixes-unstable branch Andrew Morton
2026-07-08 22:06 ` Matthew Wilcox [this message]
2026-07-09 0:22 ` Andrew Morton
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