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[2003:d8:2f38:b600:7d6d:5e38:70ec:12c6]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-447f73d4a3csm193343385e9.22.2025.05.24.14.48.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 24 May 2025 14:48:03 -0700 (PDT) Message-ID: <5815d9ed-e59f-4129-b20b-a0c07a2cf874@redhat.com> Date: Sat, 24 May 2025 23:48:01 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V2 2/2] mm/khugepaged: fix race with folio split/free using temporary reference To: Shivank Garg , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, fengwei.yin@intel.com, bharata@amd.com, syzbot+2b99589e33edbe9475ca@syzkaller.appspotmail.com References: <20250523091432.17588-1-shivankg@amd.com> <20250523091432.17588-2-shivankg@amd.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: <20250523091432.17588-2-shivankg@amd.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: MwTr-5dx9MEJGj68l3XYpCM8NrgdJOJqQuQ6J3z3TT0_1748123285 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 94EB540007 X-Stat-Signature: sznpzajckwib579ix416rdr9pgd3jnn1 X-Rspam-User: X-HE-Tag: 1748123288-87078 X-HE-Meta: U2FsdGVkX19WveeaDCSqgnK2NUde8v9nd8eZqYumpA5BAy3//voQXUF//o9h3loJRqxSfwla9iPqKqr5lqx/erVYi456i8dnzZWmKoNELZ9cf/DlQt8asBaaCTAUy6L3b22UkJBofU8YVOQ03r6KfkzFjzgEt48MtMNP8ASO736RSz1nR9DD8yNnFOtojb/kWSq/sUCAVlKhZd8E+exEwDjv80jEwltuuJQVHAaOINNDefKLpskYCvhQp+tVA1xdLbwf/lhl9ST7zD27NzJ1uVtX8fLukzcYUQU17Uoa1TcCBji97Hq/hl7LXMvV4++X5R1+7PEgYQ6FOnpkqdWYvZzm0GbRiqD+CD4Vzb/BChMqCZC2lBMAYS90/SIOV6TYK0TDNzMGqfQci7ZcAttsA6qmkcw0bB5KNu9/2KpGAZ8hzfNxBXXCXMrWRUdHlEStKNH8FB7o3Sl/uc1rq+X8fPewS7asSdVFK6ytp/dVwSLo7qCoFu/QKOd2JXJxYeTBEa+MHrwMf3Y5HiYWlNnml60CuqHr1TFQTjedwFD2sfkSHNuxxJz3WeG3TWEqxcsQEnvLpglEV9yCWLQsrSFM4TqsBrt42T4g9KJx+6unqpPQnqnhZapY8iak4AImiaFpHsB/Zx7hA5PqTQ8g5QtXfW8ChxoukFSh1fHQb5FboYHdqhVz6dHnWZGAnrdUbGiF9nuYDjyYAXxoJDM7r08+04fEg33OUSUpnCw3zMVyS0ItPXdqAeMvUSwVLTqFWPEEz81d/o/bth4uCYbM6fZLMl3VLZKfDj+Tz3Qd4mQ/YBgfByeQ2RYTH6XEB/naXCH+YtJnYsBnDDN3tBEpgcIn32R991AGvG7EvcUvFVBI4P1/hUNK7Uz2CpEKP5Z5NZq6hDWJhzjGddoIj0BrxFoLiv7JT3YhJw4SJJQQc0BRJ+6Bp3sloAD47yiXhGGZnKRNye0Q4Ttr0VeK3BEbkCZ U6xZFOZH 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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 23.05.25 11:14, Shivank Garg wrote: > hpage_collapse_scan_file() calls folio_expected_ref_count(), which in turn > calls folio_mapcount(). folio_mapcount() checks folio_test_large() before > proceeding to folio_large_mapcount(), but there is a race window where the > folio may get split/freed between these checks, triggering: > > VM_WARN_ON_FOLIO(!folio_test_large(folio), folio) > > Take a temporary reference to the folio in hpage_collapse_scan_file(). > This stabilizes the folio during refcount check and prevents incorrect > large folio detection due to concurrent split/free. > > Fixes: 05c5323b2a34 ("mm: track mapcount of large folios in single value") > Reported-by: syzbot+2b99589e33edbe9475ca@syzkaller.appspotmail.com > Closes: https://lore.kernel.org/all/6828470d.a70a0220.38f255.000c.GAE@google.com > Suggested-by: David Hildenbrand > Signed-off-by: Shivank Garg > --- > V1: https://lore.kernel.org/linux-mm/20250522093452.6379-1-shivankg@amd.com > --- Assuming we have this as patch #1: Acked-by: David Hildenbrand -- Cheers, David / dhildenb