From: "David Hildenbrand (Arm)" <david@kernel.org>
To: Wandun Chen <chenwandun1@gmail.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: akpm@linux-foundation.org, ljs@kernel.org, ziy@nvidia.com,
baolin.wang@linux.alibaba.com, liam@infradead.org,
npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com,
baohua@kernel.org, lance.yang@linux.dev
Subject: Re: [PATCH v3] mm/khugepaged: avoid underflow in madvise_collapse for sub-PMD MADV_COLLAPSE
Date: Wed, 13 May 2026 09:24:49 +0200 [thread overview]
Message-ID: <3fbd1959-8619-4c10-b191-fb7b4ba029ff@kernel.org> (raw)
In-Reply-To: <20260513055428.1664898-1-chenwandun@lixiang.com>
On 5/13/26 07:54, Wandun Chen wrote:
> From: Chen Wandun <chenwandun@lixiang.com>
>
> madvise_collapse() computes the THP-aligned window:
>
> hstart = ALIGN(start, HPAGE_PMD_SIZE); /* round up */
> hend = ALIGN_DOWN(end, HPAGE_PMD_SIZE); /* round down */
>
> The following case will cause hstart > hend, and result in underflow
> in the return statement, avoid it by returning zero early when
> hstart > hend. The return value is due to input is valid to madvise(),
> and there is nothing to collapse.
>
> madvise(PMD-aligned + PAGE_SIZE, PAGE_SIZE, MADV_COLLAPSE);
>
> In addition, kmalloc_obj(), mmgrab() and lru_add_drain_all() are
> unnecessary when hstart == hend, so skip these operations by
> returning early too.
>
> Signed-off-by: Chen Wandun <chenwandun@lixiang.com>
> ---
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
--
Cheers,
David
next prev parent reply other threads:[~2026-05-13 7:24 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-13 5:54 [PATCH v3] mm/khugepaged: avoid underflow in madvise_collapse for sub-PMD MADV_COLLAPSE Wandun Chen
2026-05-13 7:24 ` David Hildenbrand (Arm) [this message]
2026-05-13 9:24 ` Lorenzo Stoakes
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