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Wed, 17 Jun 2026 08:10:43 -0700 (PDT) Received: from hu-ketakish-hyd.qualcomm.com ([202.46.22.19]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2c42f2e5369sm173008955ad.9.2026.06.17.08.10.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Jun 2026 08:10:43 -0700 (PDT) From: Ketan Date: Wed, 17 Jun 2026 20:39:37 +0530 Subject: [PATCH] mm: page_ext: validate section in for_each_page_ext iterator Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260617-page_ext-v1-1-37ad802b1a38@oss.qualcomm.com> X-B4-Tracking: v=1; b=H4sIALC4MmoC/yXMQQ5AMBSE4avIW2uiaBeuIiJVU54F0iIScXfF8 kv+mYsCPCNQlVzkcXDgZY6QaUJ2NPMAwX005VmuMy21WM2AFucmCgmnlCqVdpZivno4Pr+ruvk d9m6C3d493fcD7ufg2WwAAAA= X-Change-ID: 20260616-page_ext-31ef555456fc To: Andrew Morton , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Luiz Capitulino , David Hildenbrand Cc: kernel@oss.qualcomm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Ketan Kishore X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; 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When dynamically adding memory in hotplug path, it can lead to a NULL pointer dereference during page_ext_lookup at the boundary of the last valid section. [ 14.555124][ T846] Call trace: [ 14.555125][ T846] lookup_page_ext+0x6c/0x108 (P) [ 14.555127][ T846] page_ext_lookup+0x30/0x3c [ 14.555129][ T846] __reset_page_owner+0x11c/0x260 [ 14.571201][ T846] __free_pages_ok+0x5e8/0x8e0 [ 14.571204][ T846] __free_pages_core+0x78/0xf0 [ 14.571206][ T846] generic_online_page+0x14/0x24 [ 14.597782][ T846] online_pages+0x178/0x30c [ 14.597784][ T846] memory_block_change_state+0x284/0x32c [ 14.597787][ T846] memory_subsys_online+0x4c/0x64 [ 14.597789][ T846] device_online+0x88/0xb0 [ 14.597791][ T846] online_memory_block+0x30/0x40 [ 14.597793][ T846] walk_memory_blocks+0xac/0xe8 [ 14.597794][ T846] add_memory_resource+0x280/0x298 [ 14.656161][ T846] add_memory+0x60/0x98 Add a valid-section check before looking up the next page_ext so the iterator stops cleanly at section boundaries. Fixes: 9039b9096ea2 ("mm: page_owner: use new iteration API") Signed-off-by: Ketan Kishore --- mm/page_ext.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/mm/page_ext.c b/mm/page_ext.c index e2e92bd27ebd..74067ea740fe 100644 --- a/mm/page_ext.c +++ b/mm/page_ext.c @@ -253,6 +253,18 @@ static struct page_ext *lookup_page_ext(const struct page *page) { unsigned long pfn = page_to_pfn(page); struct mem_section *section = __pfn_to_section(pfn); + + /* + * section can be NULL when the page_ext iterator's for-loop increment + * computes a PFN one step beyond the last registered section. This + * occurs because pfn_to_page() uses __nr_to_section() which succeeds + * for unregistered sections that share a root array with registered + * sections,while __pfn_to_section() returns NULL for them. + * + */ + if (!section) + return NULL; + struct page_ext *page_ext = READ_ONCE(section->page_ext); WARN_ON_ONCE(!rcu_read_lock_held()); --- base-commit: c425609d6ac4012c8bbf01ec2e10e801b1923a7b change-id: 20260616-page_ext-31ef555456fc Best regards, -- Ketan Kishore