From: "David Hildenbrand (Arm)" <david@kernel.org>
To: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Zi Yan <ziy@nvidia.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
"Liam R. Howlett" <liam@infradead.org>,
Nico Pache <npache@redhat.com>,
Ryan Roberts <ryan.roberts@arm.com>, Dev Jain <dev.jain@arm.com>,
Barry Song <baohua@kernel.org>, Lance Yang <lance.yang@linux.dev>,
Usama Arif <usama.arif@linux.dev>,
Pankaj Raghav <p.raghav@samsung.com>,
Hannes Reinecke <hare@suse.de>, Hugh Dickins <hughd@google.com>,
Yang Shi <shy828301@gmail.com>, Kiryl Shutsemau <kas@kernel.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Hengbin Zhang <uqbarz@gmail.com>,
stable@vger.kernel.org
Subject: Re: [PATCH mm-hotfixes 2/2] mm/huge_memory: fix huge_zero_pfn race
Date: Thu, 30 Jul 2026 14:10:23 +0200 [thread overview]
Message-ID: <39b527d7-9c6e-4798-be9d-b834c8a3d2a0@kernel.org> (raw)
In-Reply-To: <amsch6HvEH5IJjfM@lucifer>
On 7/30/26 11:55, Lorenzo Stoakes (ARM) wrote:
> On Thu, Jul 30, 2026 at 11:22:09AM +0200, David Hildenbrand (Arm) wrote:
>> [...]
>>
>>> So invariants are required - huge_zero_refcount MUST:
>>>
>>> * Only be set in the huge_zero_lock critical section to ensure
>>> serialisation of huge_zero_pfn, huge_zero_folio and huge_zero_refcount
>>> writes.
>>>
>>> * Be set non-zero only AFTER huge_zero_[pfn, folio] are set to valid values
>>> so installation of the huge zero folio on read page fault ensures
>>> concurrent is_huge_zero_*() calls correctly identify the huge zero folio.
>>>
>>> * Be set zero only BEFORE huge_zero_[pfn, folio] are set to NULL and ~0UL
>>> respectively, and atomically.
>>>
>>> Establish these by:
>>>
>>> * Only updating huge_zero_refcount in the huge_zero_lock critical section
>>> in get_huge_zero_folio() and shrink_huge_zero_folio_scan().
>>
>> That is imprecise. huge_zero_refcount is updated (incremented) outside of
>> huge_zero_lock in get_huge_zero_folio().
>
> You're right.
>
> ->
>
> * Only setting huge_zero_refcount to zero or an absolute value in the
> huge_zero_lock critical section in get_huge_zero_folio() and
> shrink_huge_zero_folio_scan() and updating atomically elsewhere.
>
> Seems better?
Yes, I guess the transition from/to 0 are the problematic bits. Everything else
can just be lockless.
--
Cheers,
David
next prev parent reply other threads:[~2026-07-30 12:10 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-28 12:05 [PATCH mm-hotfixes 0/2] mm/huge_memory: fix huge_zero_pfn race Lorenzo Stoakes (ARM)
2026-07-28 12:05 ` [PATCH mm-hotfixes 1/2] mm/huge_memory: separate out CONFIG_PERSISTENT_HUGE_ZERO_FOLIO logic Lorenzo Stoakes (ARM)
2026-07-28 15:08 ` Kiryl Shutsemau
2026-07-28 15:41 ` Lorenzo Stoakes (ARM)
2026-07-28 12:05 ` [PATCH mm-hotfixes 2/2] mm/huge_memory: fix huge_zero_pfn race Lorenzo Stoakes (ARM)
2026-07-30 9:22 ` David Hildenbrand (Arm)
2026-07-30 9:55 ` Lorenzo Stoakes (ARM)
2026-07-30 12:10 ` David Hildenbrand (Arm) [this message]
2026-07-30 13:09 ` Lorenzo Stoakes (ARM)
2026-07-28 19:02 ` [PATCH mm-hotfixes 0/2] " David Hildenbrand (Arm)
2026-07-29 8:15 ` Lorenzo Stoakes (ARM)
2026-07-30 0:55 ` Andrew Morton
2026-07-30 9:05 ` David Hildenbrand (Arm)
2026-07-30 9:15 ` Lorenzo Stoakes (ARM)
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=39b527d7-9c6e-4798-be9d-b834c8a3d2a0@kernel.org \
--to=david@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=baohua@kernel.org \
--cc=baolin.wang@linux.alibaba.com \
--cc=dev.jain@arm.com \
--cc=hare@suse.de \
--cc=hughd@google.com \
--cc=kas@kernel.org \
--cc=lance.yang@linux.dev \
--cc=liam@infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=ljs@kernel.org \
--cc=npache@redhat.com \
--cc=p.raghav@samsung.com \
--cc=ryan.roberts@arm.com \
--cc=shy828301@gmail.com \
--cc=stable@vger.kernel.org \
--cc=uqbarz@gmail.com \
--cc=usama.arif@linux.dev \
--cc=ziy@nvidia.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox