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[2003:cb:c714:1700:305a:4df7:c043:7a59]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38f259f85c2sm23455945f8f.91.2025.02.21.00.13.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 21 Feb 2025 00:13:59 -0800 (PST) Message-ID: Date: Fri, 21 Feb 2025 09:13:58 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/migrate_device: Do not access pgmap for non zone device pages To: Alistair Popple , Balbir Singh Cc: akpm@linux-foundation.org, linux-mm@kvack.org, Jason Gunthorpe , Dan Williams References: <20250219231337.364133-1-balbirs@nvidia.com> <329060a2-8871-4adf-9a45-f0afaedc8848@redhat.com> <22cff2d7-a9db-4a86-a168-d610fc00cdd9@nvidia.com> <66467b8d-9e8c-4a74-b932-9ddc3fcf459a@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: K_QsPPFDWCQtUu9DDz1Iv8wpyjic2t2Tbogz1akZaGk_1740125641 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: AACD580005 X-Stat-Signature: rnufw1mn94io4e5h55amatd4cegndtau X-Rspamd-Server: rspam03 X-HE-Tag: 1740125643-37260 X-HE-Meta: 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 dmSdswUn 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000038, 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 20.02.25 23:45, Alistair Popple wrote: > On Thu, Feb 20, 2025 at 11:38:10PM +1100, Balbir Singh wrote: >> On 2/20/25 23:05, David Hildenbrand wrote: >>> On 20.02.25 12:58, Balbir Singh wrote: >>>> On 2/20/25 22:48, David Hildenbrand wrote: >>>>> On 20.02.25 00:13, Balbir Singh wrote: >>>>>> page_pgmap() is referenced before checking if the page is a zone >>>>>> device page and this triggers the warning in page_pgmap(). Refactor >>>>>> the code to use the helper function after relevant checks. >>>>>> >>>>>> Cc: Alistair Popple >>>>>> Cc: Jason Gunthorpe >>>>>> Cc: David Hildenbrand >>>>>> Cc: Dan Williams >>>>>> >>>>>> Signed-off-by: Balbir Singh >>>>>> --- >>>>>> >>>>>> Fixes: 7f1cfd71153b ("mm: allow compound zone device pages") on >>>>>> mm-unstable >>>>> >>>>> Is there actually something broken? At least for now, reading folio->pgmap should just work, although it might be garbage. >>>>> >>>> >>>> It triggers the VM_WARN_ON_ONCE_PAGE >>>> >>>> static inline struct dev_pagemap *page_pgmap(const struct page *page) >>>> { >>>>     VM_WARN_ON_ONCE_PAGE(!is_zone_device_page(page), page); >>>>     return page_folio(page)->pgmap; >>>> } >>>> >>>> Nothing is broken, because the code below has checks for is_device_coherent_page(), >>>> but in general I think the WARN_ON is correct because it warns us against garbage >>>> and it's propagation if the correct checks are not in place. >>> >>> Ah! Now I read your "triggers the warning in page_pgmap()" in the description. >>> >>> It's usually a good idea to just include the splat you observed, if you did, and call it "triggers the VM_WARN_ON_ONCE_PAGE". >> >> Sure >> >>> >>> The "Fixes:" should go above the "---" in that case. >> >> I was not sure if the commit-ids in mm-unstable are persistent, so I put it >> below the --- to avoid confusion > > They are not, but I'm unsure what the process is here. I guess either I roll > this fix into my series and repost or maybe Andrew takes it as is a separate fix > on top of my series? Ah, I completely ignored that this is not in mm/mm-stable yet. Yes, that should best just be squashed into the original commit as long as it is not in mm/mm-stable. -- Cheers, David / dhildenb