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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38dd8dee385sm7263297f8f.61.2025.02.11.01.37.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 11 Feb 2025 01:37:56 -0800 (PST) Message-ID: <2b0bb476-5bd6-489a-9b9e-7aa20964abfa@redhat.com> Date: Tue, 11 Feb 2025 10:37:54 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [REGRESSION] NULL pointer dereference on ARM (AT91SAM9G25) during compaction To: Qi Zheng Cc: "Russell King (Oracle)" , Ezra Buehler , linux-mm@kvack.org, Andrew Morton , "Mike Rapoport (Microsoft)" , Muchun Song , Vlastimil Babka , Ryan Roberts , "Vishal Moola (Oracle)" , Hugh Dickins , Matthew Wilcox , Peter Xu , Nicolas Ferre , Alexandre Belloni , Claudiu Beznea , open list , linux-arm-kernel@lists.infradead.org References: <5d50d714-197f-44c0-94e0-ff70ee51e866@bytedance.com> <34bcf011-b4ac-479c-92ce-852623e73039@redhat.com> <3f7babee-b232-4e6b-a896-947150dcd1ef@bytedance.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Stat-Signature: 356unx6hu6h35wquit3bo11xbywzaxpj X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 144E71C0009 X-Rspam-User: X-HE-Tag: 1739266681-722985 X-HE-Meta: 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 PxRs6Rc5 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11.02.25 10:29, Qi Zheng wrote: > > > On 2025/2/11 17:14, David Hildenbrand wrote: >> On 11.02.25 04:45, Qi Zheng wrote: >>> Hi Russell, >>> >>> On 2025/2/11 01:03, Russell King (Oracle) wrote: >>>> On Mon, Feb 10, 2025 at 05:49:38PM +0100, Ezra Buehler wrote: >>>>> When running vanilla Linux 6.13 or newer (6.14-rc2) on the >>>>> AT91SAM9G25-based GARDENA smart Gateway, we are seeing a NULL pointer >>>>> dereference resulting in a kernel panic. The culprit seems to be commit >>>>> fc9c45b71f43 ("arm: adjust_pte() usepte_offset_map_rw_nolock()"). >>>>> Reverting the commit apparently fixes the issue. >>>> >>>> The blamed commit is buggy: >>>> >>>> arch/arm/include/asm/tlbflush.h: >>>> #define update_mmu_cache(vma, addr, ptep) \ >>>>           update_mmu_cache_range(NULL, vma, addr, ptep, 1) >>>> >>>> So vmf can be NULL. This didn't used to matter before this commit, >>>> because vmf was not used by ARM's update_mmu_cache_range(). However, >>>> the commit introduced a dereference of it, which now causes a NULL >>>> point dereference. >>>> >>>> Not sure what the correct solution is, but at a guess, both: >>>> >>>>     if (ptl != vmf->ptl) >>>> >>>> need to become: >>>> >>>>     if (!vmf || ptl != vmf->ptl) >>> >>> No, we can't do that, because without using split PTE locks, we would >>> use shared mm->page_table_lock, which would create a deadlock. >> >> Maybe we can simply special-case on CONFIG_SPLIT_PTE_PTLOCKS ? >> >> if (IS_ENABLED(CONFIG_SPLIT_PTE_PTLOCKS)) { > > In this case, if two vmas map the same PTE page, then the same PTE lock > will be held repeatedly. Right? Hmm, the comment says: /* * This is called while another page table is mapped, so we * must use the nested version. This also means we need to * open-code the spin-locking. */ "another page table" implies that it cannot be the same. But maybe that comment was also wrong? -- Cheers, David / dhildenb