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[2003:d8:2f28:7c00:a95e:ac49:f2ad:ab84]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a35ca5a841sm16793693f8f.34.2025.05.20.07.05.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 20 May 2025 07:05:37 -0700 (PDT) Message-ID: Date: Tue, 20 May 2025 16:05:35 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [syzbot] [mm?] WARNING in folio_large_mapcount To: Shivank Garg , syzbot , Liam.Howlett@oracle.com, akpm@linux-foundation.org, baolin.wang@linux.alibaba.com, dev.jain@arm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, npache@redhat.com, ryan.roberts@arm.com, syzkaller-bugs@googlegroups.com, ziy@nvidia.com, Matthew Wilcox References: <6828470d.a70a0220.38f255.000c.GAE@google.com> <5cdc53ff-ff48-4deb-9551-92bd47590a53@redhat.com> <7d20b14c-5739-4556-9f6e-d19cc7e3ee9b@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: <7d20b14c-5739-4556-9f6e-d19cc7e3ee9b@amd.com> X-Mimecast-Spam-Score: 1 X-Mimecast-MFC-PROC-ID: 4Cb3pKzXONkGQoSRg_FsqQbEIuAFTo1FRODd6fEzOWw_1747749938 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: 50F01120011 X-Rspam-User: X-Stat-Signature: mht8jecrd4mo6rwjn647bdgzwd71mh1p X-HE-Tag: 1747749941-340199 X-HE-Meta: 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 l+2islm6 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 LanSKrLa jZJN1Jbip3ABVPLZIfHDL5C9rLqGd24czq9JO4ojDgkkeVHDg1Cdq9uc3xR6NO+H9MmSt5tQGObgbzBfWaWWqK6Q9San4OzoRtEgQ/xRam4= 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 20.05.25 07:45, Shivank Garg wrote: > On 5/19/2025 6:56 PM, David Hildenbrand wrote: >> On 17.05.25 10:21, syzbot wrote: >>> Hello, >>> >>> syzbot found the following issue on: >>> >>> HEAD commit:    627277ba7c23 Merge tag 'arm64_cbpf_mitigation_2025_05_08' .. >>> git tree:       upstream >>> console output: https://syzkaller.appspot.com/x/log.txt?x=1150f670580000 >>> kernel config:  https://syzkaller.appspot.com/x/.config?x=5929ac65be9baf3c >>> dashboard link: https://syzkaller.appspot.com/bug?extid=2b99589e33edbe9475ca >>> compiler:       Debian clang version 20.1.2 (++20250402124445+58df0ef89dd6-1~exp1~20250402004600.97), Debian LLD 20.1.2 >>> >>> Unfortunately, I don't have any reproducer for this issue yet. >>> >>> Downloadable assets: >>> disk image: https://storage.googleapis.com/syzbot-assets/0a42ae72fe0e/disk-627277ba.raw.xz >>> vmlinux: https://storage.googleapis.com/syzbot-assets/0be88297bb66/vmlinux-627277ba.xz >>> kernel image: https://storage.googleapis.com/syzbot-assets/31808a4b1210/bzImage-627277ba.xz >>> >>> IMPORTANT: if you fix the issue, please add the following tag to the commit: >>> Reported-by: syzbot+2b99589e33edbe9475ca@syzkaller.appspotmail.com >>> >>> ------------[ cut here ]------------ >>> WARNING: CPU: 1 PID: 38 at ./include/linux/mm.h:1335 folio_large_mapcount+0xd0/0x110 include/linux/mm.h:1335 >> >> This should be >> >> VM_WARN_ON_FOLIO(!folio_test_large(folio), folio); >> >>> Modules linked in: >>> CPU: 1 UID: 0 PID: 38 Comm: khugepaged Not tainted 6.15.0-rc6-syzkaller-00025-g627277ba7c23 #0 PREEMPT(full) >>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025 >>> RIP: 0010:folio_large_mapcount+0xd0/0x110 include/linux/mm.h:1335 >>> Code: 04 38 84 c0 75 29 8b 03 ff c0 5b 41 5e 41 5f e9 96 d2 2b 09 cc e8 d0 cb 99 ff 48 89 df 48 c7 c6 20 de 77 8b e8 a1 dc de ff 90 <0f> 0b 90 eb b6 89 d9 80 e1 07 80 c1 03 38 c1 7c cb 48 89 df e8 87 >>> RSP: 0018:ffffc90000af77e0 EFLAGS: 00010246 >>> RAX: e1fcb38c0ff8ce00 RBX: ffffea00014c8000 RCX: e1fcb38c0ff8ce00 >>> RDX: 0000000000000001 RSI: ffffffff8d9226df RDI: ffff88801e2fbc00 >>> RBP: ffffc90000af7b50 R08: ffff8880b8923e93 R09: 1ffff110171247d2 >>> R10: dffffc0000000000 R11: ffffed10171247d3 R12: 1ffffd4000299000 >>> R13: dffffc0000000000 R14: 0000000000000000 R15: dffffc0000000000 >>> FS:  0000000000000000(0000) GS:ffff8881261fb000(0000) knlGS:0000000000000000 >>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>> CR2: 00007ffe58f12dc0 CR3: 0000000030e04000 CR4: 00000000003526f0 >>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >>> Call Trace: >>>   >>>   folio_mapcount include/linux/mm.h:1369 [inline] >> >> And here we come through >> >> if (likely(!folio_test_large(folio))) { >>     ... >> } >> return folio_large_mapcount(folio); >> >> >> So the folio is split concurrently. And I think there is nothing stopping it from getting freed. >> >> We do a xas_for_each() under RCU. So yes, this is racy. >> >> In  collapse_file(), we re-validate everything. >> >> We could >> >> (A) Take proper pagecache locks >> >> (B) Try grabbing a temporary folio reference >> >> (C) Try snapshotting the folio >> >> Probably, in this code, (B) might be cleanest for now? Handling it just like other code in mm/filemap.c. >> > > Hi, Hi, > > I've implemented your suggestion (B) using folio_try_get(). > Could you please review if my patch looks correct? You should probably drop both comments, the code merely mimics what filemap.c does. Apart from that, nothing jumped at me. -- Cheers, David / dhildenb