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[2003:cb:c732:e600:4982:2903:710f:f20a]) by smtp.gmail.com with ESMTPSA id bq21-20020a5d5a15000000b00341cb22a8d4sm14229799wrb.108.2024.04.02.05.58.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 02 Apr 2024 05:58:52 -0700 (PDT) Message-ID: <736b982a-57c9-441a-812c-87cdee2e096e@redhat.com> Date: Tue, 2 Apr 2024 14:58:50 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv2 1/1] mm: fix unproperly folio_put by changing API in read_pages To: "zhaoyang.huang" , Andrew Morton , NeilBrown , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Zhaoyang Huang , steve.kang@unisoc.com Cc: Matthew Wilcox , Christoph Hellwig References: <20240401081734.1433755-1-zhaoyang.huang@unisoc.com> Content-Language: en-US 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: <20240401081734.1433755-1-zhaoyang.huang@unisoc.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 01.04.24 10:17, zhaoyang.huang wrote: > From: Zhaoyang Huang > > An VM_BUG_ON in step 9 of [1] could happen as the refcnt is dropped > unproperly during the procedure of read_pages()->readahead_folio->folio_put. > This is introduced by commit 9fd472af84ab ("mm: improve cleanup when > ->readpages doesn't process all pages")'. > > key steps of[1] in brief: > 2'. Thread_truncate get folio to its local fbatch by find_get_entry in step 2 > 7'. Last refcnt remained which is not as expect as from alloc_pages > but from thread_truncate's local fbatch in step 7 > 8'. Thread_reclaim succeed to isolate the folio by the wrong refcnt(not > the value but meaning) in step 8 > 9'. Thread_truncate hit the VM_BUG_ON in step 9 > > [1] > Thread_readahead: > 0. folio = filemap_alloc_folio(gfp_mask, 0); > (refcount 1: alloc_pages) > 1. ret = filemap_add_folio(mapping, folio, index + i, gfp_mask); > (refcount 2: alloc_pages, page_cache) > > Thread_truncate: > 2. folio = find_get_entries(&fbatch_truncate); > (refcount 3: alloc_pages, page_cache, fbatch_truncate)) > > Thread_readahead: > 3. Then we call read_pages() > First we call ->readahead() which for some reason stops early. > 4. Then we call readahead_folio() which calls folio_put() > (refcount 2: page_cache, fbatch_truncate) > 5. Then we call folio_get() > (refcount 3: page_cache, fbatch_truncate, read_pages_temp) > 6. Then we call filemap_remove_folio() > (refcount 2: fbatch_truncate, read_pages_temp) > 7. Then we call folio_unlock() and folio_put() > (refcount 1: fbatch_truncate) > > Thread_reclaim: > 8. collect the page from LRU and call shrink_inactive_list->isolate_lru_folios > shrink_inactive_list > { > isolate_lru_folios > { > if (!folio_test_lru(folio)) //false > bail out; > if (!folio_try_get(folio)) //false > bail out; > } > } > (refcount 2: fbatch_truncate, reclaim_isolate) > > 9. call shrink_folio_list->__remove_mapping > shrink_folio_list() > { > folio_try_lock(folio); > __remove_mapping() > { > if (!folio_ref_freeze(2)) //false > bail out; > } > folio_unlock(folio) > list_add(folio, free_folios); > } > (folio has refcount 0) > > Thread_truncate: > 10. Thread_truncate will hit the refcnt VM_BUG_ON(refcnt == 0) in > release_pages->folio_put_testzero > truncate_inode_pages_range > { > folio = find_get_entries(&fbatch_truncate); > truncate_inode_pages(&fbatch_truncate); > folio_fbatch_release(&fbatch_truncate); > { > folio_put_testzero(folio); //VM_BUG_ON here > } > } > > fix: commit 9fd472af84ab ("mm: improve cleanup when ->readpages doesn't process all pages")' Something that would help here is an actual reproducer that triggersthis issue. To me, it's unclear at this point if we are talking about an actual issue or a theoretical issue? -- Cheers, David / dhildenb