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[2003:cb:c70c:de00:1200:8636:b63b:f43]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3825490c2easm4396200f8f.29.2024.11.21.01.46.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 21 Nov 2024 01:46:24 -0800 (PST) Message-ID: <7bab1234-45d7-43f6-8ebf-4a2c923c6a46@redhat.com> Date: Thu, 21 Nov 2024 10:46:23 +0100 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: [syzbot] [mm?] BUG: Bad page state in iomap_write_begin From: David Hildenbrand To: syzbot , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com Cc: David Howells References: <673d9fc5.050a0220.363a1b.0007.GAE@google.com> Content-Language: en-US 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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 21.11.24 10:26, David Hildenbrand wrote: > On 20.11.24 09:37, syzbot wrote: >> Hello, >> >> syzbot found the following issue on: >> >> HEAD commit: e8bdb3c8be08 Merge tag 'riscv-for-linus-6.12-rc8' of git:/.. >> git tree: upstream >> console output: https://syzkaller.appspot.com/x/log.txt?x=1644d2c0580000 >> kernel config: https://syzkaller.appspot.com/x/.config?x=d2aeec8c0b2e420c >> dashboard link: https://syzkaller.appspot.com/bug?extid=c317c107c68f8bc257d9 >> compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40 >> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1144d2c0580000 >> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=176252e8580000 >> >> Downloadable assets: >> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-e8bdb3c8.raw.xz >> vmlinux: https://storage.googleapis.com/syzbot-assets/fcae16ff0e0f/vmlinux-e8bdb3c8.xz >> kernel image: https://storage.googleapis.com/syzbot-assets/758973beace8/bzImage-e8bdb3c8.xz >> mounted in repro #1: https://storage.googleapis.com/syzbot-assets/a097a300c8a9/mount_0.gz >> mounted in repro #2: https://storage.googleapis.com/syzbot-assets/36b9fff6ab5e/mount_6.gz >> >> IMPORTANT: if you fix the issue, please add the following tag to the commit: >> Reported-by: syzbot+c317c107c68f8bc257d9@syzkaller.appspotmail.com >> >> BUG: Bad page state in process syz-executor315 pfn:49e01 >> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x49e01 >> head: order:0 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:-1 > > So, we have a pincount underflow on a large folio (order-9). We > allocated the folio in iomap_write_begin()->__iomap_get_folio(). Nothing > special. > > [...] > >> >> BUG: Bad page state in process syz-executor315 pfn:49e00 >> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x49e00 >> head: order:0 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0 >> flags: 0x4fff0000000004d(locked|referenced|uptodate|head|node=1|zone=1|lastcpupid=0x7ff) >> raw: 04fff0000000004d dead000000000100 dead000000000122 0000000000000000 >> raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000 >> head: 04fff0000000004d dead000000000100 dead000000000122 0000000000000000 >> head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000 >> head: 04fff00000000000 0000000000000000 ffffffffffffffff 0000000000000000 >> head: 0000000000000200 0000000000000000 00000000ffffffff 0000000000000000 >> page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set > > And we seem to have an unexpected flag set on the head page of the same > large folio. Likely PG_locked. > > ... > >> XFS (loop0): Unmounting Filesystem 9f1cad42-11bd-4e12-8f0b-f07876b81d9a >> BUG: Bad page state in process syz-executor315 pfn:49c01 >> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x49c01 >> head: order:0 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:-1 >> flags: 0x4fff0000000004d(locked|referenced|uptodate|head|node=1|zone=1|lastcpupid=0x7ff) >> raw: 04fff00000000000 ffffea0001270001 ffffffffffffffff ffffffff00000000 >> raw: 0000000000000200 0000000000000000 00000000ffffffff 0000000000000000 >> head: 04fff0000000004d dead000000000100 dead000000000122 0000000000000000 >> head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000 >> head: 04fff00000000000 ffffea0001270001 ffffffffffffffff ffffffff00000000 >> head: 0000000000000200 0000000000000000 00000000ffffffff 0000000000000000 >> page dumped because: nonzero pincount > > [...] > >> >> BUG: Bad page state in process syz-executor315 pfn:49c00 >> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x49c00 >> head: order:0 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0 >> flags: 0x4fff0000000004d(locked|referenced|uptodate|head|node=1|zone=1|lastcpupid=0x7ff) >> raw: 04fff0000000004d dead000000000100 dead000000000122 0000000000000000 >> raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000 >> head: 04fff0000000004d dead000000000100 dead000000000122 0000000000000000 >> head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000 >> head: 04fff00000000000 0000000000000000 ffffffffffffffff 0000000000000000 >> head: 0000000000000200 0000000000000000 00000000ffffffff 0000000000000000 >> page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set >> page_owner tracks the page as allocated > > Same thing, different folio. > > > So we seem to be repeatedly freeing a large folio that > (a) Is locked > (b) Has a pincount underflow > > Likely because we have an unbalanced unpin, that happens before > evicting/truncating the folio. If we then evict/truncate the (locked) > folio, we free the folio before unlocking it and dropping the actual > last reference. > > Not sure why we see a comparable thing with small folios (pincount part > of refcount, but on unpin our refcount should seriously underflow > immediately) > > CCing David If I get the reproducer right, it does: (1) Create a temporary folder and chdir into it (2) Mounts an (XFS?) image (syz_mount_image() magic ) (3) Opens a file1 in there (4) Writes some data into it using write(). Likely this allocates the folios. (5) Mmaps the file1 (MAP_UNINITIALIZED|MAP_LOCKED|MAP_FIXED|MAP_SHARED) (6) Creates a socket -- socket() -- and binds it -- bind(). (7) Writes some more data into the mmap of file1 using memcpy. (8) Mounts another (?) image (syz_mount_image() magic ) (9) Opens a file2 in there with O_SYNC|O_DIRECT|O_CREAT|O_RDWR. (10) Calls ioctl(0xc0185879) on the file2 (11) Calls sendmsg() on the socket. msghdr and all data seems to reside completely in the mmap of file1. (12) Calls symlink(0,0) (13) Calls rename(0,0) I doubt 12+13 are relevant. Likely (11) is the problematic bit: we are performing direct-io on folios allocated during (4) from file1 into file2. I have not deciphered yet what the ioctl in (10) does. It triggers on first attempt, so it doesn't seem to be racy. -- Cheers, David / dhildenb