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[2003:d8:2f4e:fd00:8e13:e3b5:90c8:1159]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-453647070cesm115773945e9.33.2025.06.23.09.59.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 Jun 2025 09:59:20 -0700 (PDT) Message-ID: <6f92b7d6-7d3c-4830-a591-75dc4d55c46c@redhat.com> Date: Mon, 23 Jun 2025 18:59:19 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [syzbot] [mm?] kernel BUG in sanity_check_pinned_pages To: Pavel Begunkov , Jens Axboe , Alexander Potapenko Cc: syzbot , akpm@linux-foundation.org, catalin.marinas@arm.com, jgg@ziepe.ca, jhubbard@nvidia.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, peterx@redhat.com, syzkaller-bugs@googlegroups.com References: <6857299a.a00a0220.137b3.0085.GAE@google.com> <56862a1d-71c0-4f07-9c1a-9d70069b4d9e@redhat.com> <014a3820-8082-43a6-8bb2-70859cabdbc0@kernel.dk> 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: RIYP5J1TMk4yBrEanv9pHv5KVuCc4IP-Wupfui-oI2o_1750697961 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 58B0640002 X-Stat-Signature: y6n1gm533znw8hqm8tdo634e11suqfaf X-Rspam-User: X-HE-Tag: 1750697966-698363 X-HE-Meta: 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 b+R1Teit hnUWr9SC5odF83GUYEZ1YLnaOm2B2XCpG5PGQGG44JSgtZCN93xSSvL0yVlPFCsfFRBp3zUnETDI1Ul+L8qI4QTSHXwltxZJ53SJ7zcuYIfF9xRwcZiAypSP2+X+RPeCXq7aAYdXNBpohnSveV9/y5Lvs8dHJ6rSKS7j6hZCYGM3cGR+NhbUAsO0yxOKnEMY1rD7L9eZSsgG8CUK5BON/IrkPPS/sbNGzmWzBgxCquKeZ2Ea2YKyoBRoPxkax/k5QT63F259Wolv+3bgtX10StAEA9NKqWl7cZORl85xI6I5+Jy4kjtC2AOUYhN8G8qhGPTu+kQSEi+MZ+ME34poDD8E6pZz3MzU6BqoCW4/b6NYDi/0XvgW95oV0XxfQ4JETpG8vYg0wr5uBVwjHcx84I/6BAVyzMYcdH30fFFOMCPWSaeaWgEiAIX+qkcE6YxjjAdpMDoMb6uxInO6lmfdSEjLemWXwjf2FDQhDHJSsge+IW3jaRjP/uCqUIVHkqtEhQN+NeXFqpyzKiEdY9+68xbd1yLmmmDanHmOHyazrc8fSy1rGAHbK5selDJr5UUKQl4hO8CIhGHSotvFHFyV4iuW94Fm8+dNl5oM6IJnZHK4/mPkHYgDi1xuWq2CgJ/NlQM/DIbLeugLlhbxt3b6qnpMi8B5zO5f1HLto585iOAH45OE= 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 23.06.25 18:48, Pavel Begunkov wrote: > On 6/23/25 16:11, David Hildenbrand wrote: >> On 23.06.25 16:58, Jens Axboe wrote: >>> On 6/23/25 6:22 AM, David Hildenbrand wrote: >>>> On 23.06.25 12:10, David Hildenbrand wrote: >>>>> On 23.06.25 11:53, Alexander Potapenko wrote: >>>>>> On Mon, Jun 23, 2025 at 11:29?AM 'David Hildenbrand' via >>>>>> syzkaller-bugs wrote: >>>>>>> > ...>>> When only pinning a single tail page (iovec.iov_len = pagesize), it works as expected. >>>> >>>> So, if we pinned two tail pages but end up calling io_release_ubuf()->unpin_user_page() >>>> on the head page, meaning that "imu->bvec[i].bv_page" points at the wrong folio page >>>> (IOW, one we never pinned). >>>> >>>> So it's related to the io_coalesce_buffer() machinery. >>>> >>>> And in fact, in there, we have this weird logic: >>>> >>>> /* Store head pages only*/ >>>> new_array = kvmalloc_array(nr_folios, sizeof(struct page *), GFP_KERNEL); >>>> ... >>>> >>>> >>>> Essentially discarding the subpage information when coalescing tail pages. >>>> >>>> >>>> I am afraid the whole io_check_coalesce_buffer + io_coalesce_buffer() logic might be >>>> flawed (we can -- in theory -- coalesc different folio page ranges in >>>> a GUP result?). >>>> >>>> @Jens, not sure if this only triggers a warning when unpinning or if we actually mess up >>>> imu->bvec[i].bv_page, to end up pointing at (reading/writing) pages we didn't even pin in the first >>>> place. >>>> >>>> Can you look into that, as you are more familiar with the logic? >>> >>> Leaving this all quoted and adding Pavel, who wrote that code. I'm >>> currently away, so can't look into this right now. > > Chenliang Li did, but not like it matters > >> I did some more digging, but ended up being all confused about io_check_coalesce_buffer() and io_imu_folio_data(). >> >> Assuming we pass a bunch of consecutive tail pages that all belong to the same folio, then the loop in io_check_coalesce_buffer() will always >> run into the >> >> if (page_folio(page_array[i]) == folio && >>     page_array[i] == page_array[i-1] + 1) { >>     count++; >>     continue; >> } >> >> case, making the function return "true" ... in io_coalesce_buffer(), we then store the head page ... which seems very wrong. >> >> In general, storing head pages when they are not the first page to be coalesced seems wrong. > > Yes, it stores the head page even if the range passed to > pin_user_pages() doesn't cover the head page. > > It should be converted to unpin_user_folio(), which doesn't seem > to do sanity_check_pinned_pages(). Do you think that'll be enough > (conceptually)? Nobody is actually touching the head page in those > cases apart from the final unpin, and storing the head page is > more convenient than keeping folios. I'll take a look if it can > be fully converted to folios w/o extra overhead. Assuming we had from GUP nr_pages = 2 pages[0] = folio_page(folio, 1) pages[1] = folio_page(folio, 2) After io_coalesce_buffer() we have nr_pages = 1 pages[0] = folio_page(folio, 0) Using unpin_user_folio() in all places where we could see something like that would be the right thing to do. The sanity checks are not in unpin_user_folio() for exactly that reason: we don't know which folio pages we pinned. But now I wonder where you make sure that "Nobody is actually touching the head page"? How do you get back the "which folio range" information after io_coalesce_buffer() ? If you rely on alignment in virtual address space for you, combined with imu->folio_shift, that might not work reliably ... -- Cheers, David / dhildenb