From: Baolin Wang <baolin.wang@linux.alibaba.com>
To: "Lorenzo Stoakes (Oracle)" <ljs@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@kernel.org>, Zi Yan <ziy@nvidia.com>,
"Liam R . Howlett" <Liam.Howlett@oracle.com>,
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>,
Vlastimil Babka <vbabka@kernel.org>,
Mike Rapoport <rppt@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Michal Hocko <mhocko@suse.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 4/9] mm/huge_memory: handle buggy PMD entry in zap_huge_pmd()
Date: Fri, 20 Mar 2026 11:20:03 +0800 [thread overview]
Message-ID: <87a5618e-3ae8-43f7-b0a2-3c1e808277df@linux.alibaba.com> (raw)
In-Reply-To: <1ec18767b106a1ee1ed6e33e332c3ad5531dc636.1773924928.git.ljs@kernel.org>
On 3/19/26 9:00 PM, Lorenzo Stoakes (Oracle) wrote:
> A recent bug I analysed [0] managed to, through a bug in the userfaultfd
> implementation, reach an invalid point in the zap_huge_pmd() code where the
> PMD was none of:
>
> - A non-DAX, PFN or mixed map.
> - The huge zero folio
> - A present PMD entry
> - A softleaf entry
>
> The code at this point calls folio_test_anon() on a known-NULL
> folio. Having logic like this explicitly NULL dereference in the code is
> hard to understand, and makes debugging potentially more difficult.
>
> Add an else branch to handle this case and WARN().
>
> [0]:https://lore.kernel.org/all/6b3d7ad7-49e1-407a-903d-3103704160d8@lucifer.local/
>
> Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
LGTM.
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
next prev parent reply other threads:[~2026-03-20 3:20 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-19 13:00 [PATCH v2 0/9] mm/huge_memory: refactor zap_huge_pmd() Lorenzo Stoakes (Oracle)
2026-03-19 13:00 ` [PATCH v2 1/9] mm/huge_memory: simplify vma_is_specal_huge() Lorenzo Stoakes (Oracle)
2026-03-19 16:52 ` Kiryl Shutsemau
2026-03-19 17:16 ` Lorenzo Stoakes (Oracle)
2026-03-19 13:00 ` [PATCH v2 2/9] mm/huge: avoid big else branch in zap_huge_pmd() Lorenzo Stoakes (Oracle)
2026-03-19 13:00 ` [PATCH v2 3/9] mm/huge_memory: have zap_huge_pmd return a boolean, add kdoc Lorenzo Stoakes (Oracle)
2026-03-19 13:00 ` [PATCH v2 4/9] mm/huge_memory: handle buggy PMD entry in zap_huge_pmd() Lorenzo Stoakes (Oracle)
2026-03-20 3:20 ` Baolin Wang [this message]
2026-03-19 13:00 ` [PATCH v2 5/9] mm/huge_memory: add a common exit path to zap_huge_pmd() Lorenzo Stoakes (Oracle)
2026-03-20 3:27 ` Baolin Wang
2026-03-19 13:00 ` [PATCH v2 6/9] mm/huge_memory: remove unnecessary VM_BUG_ON_PAGE() Lorenzo Stoakes (Oracle)
2026-03-20 3:31 ` Baolin Wang
2026-03-19 13:00 ` [PATCH v2 7/9] mm/huge_memory: deduplicate zap deposited table call Lorenzo Stoakes (Oracle)
2026-03-19 17:03 ` Kiryl Shutsemau
2026-03-19 17:18 ` Lorenzo Stoakes (Oracle)
2026-03-19 21:56 ` Kiryl Shutsemau
2026-03-20 13:59 ` Lorenzo Stoakes (Oracle)
2026-03-20 14:14 ` Lorenzo Stoakes (Oracle)
2026-03-19 13:00 ` [PATCH v2 8/9] mm/huge_memory: deduplicate zap_huge_pmd() further by tracking state Lorenzo Stoakes (Oracle)
2026-03-20 3:49 ` Baolin Wang
2026-03-20 13:51 ` Lorenzo Stoakes (Oracle)
2026-03-21 5:15 ` Baolin Wang
2026-03-19 13:00 ` [PATCH v2 9/9] mm/huge_memory: have zap_huge_pmd() use vm_normal_folio_pmd() Lorenzo Stoakes (Oracle)
2026-03-20 3:09 ` [PATCH v2 0/9] mm/huge_memory: refactor zap_huge_pmd() Andrew Morton
2026-03-20 13:27 ` Lorenzo Stoakes (Oracle)
2026-03-21 3:21 ` Roman Gushchin
2026-03-21 3:33 ` Andrew Morton
2026-03-22 0:15 ` Andrew Morton
2026-03-22 2:12 ` Roman Gushchin
2026-03-23 11:19 ` Lorenzo Stoakes (Oracle)
2026-03-23 11:24 ` David Hildenbrand (Arm)
2026-03-23 11:31 ` Lorenzo Stoakes (Oracle)
2026-03-23 12:34 ` Pedro Falcato
2026-03-23 21:36 ` Andrew Morton
2026-03-23 23:27 ` Pedro Falcato
2026-03-24 0:05 ` Andrew Morton
2026-03-24 7:35 ` Lorenzo Stoakes (Oracle)
2026-03-24 7:58 ` Mike Rapoport
2026-03-24 9:55 ` Lorenzo Stoakes (Oracle)
2026-03-24 1:08 ` Roman Gushchin
2026-03-24 7:56 ` Lorenzo Stoakes (Oracle)
2026-03-24 15:24 ` Roman Gushchin
2026-03-24 18:05 ` Lorenzo Stoakes (Oracle)
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