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[2003:cb:c744:ac00:ef5c:b66d:1075:254a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-37ccca61e15sm2657340f8f.88.2024.09.26.03.48.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 26 Sep 2024 03:48:20 -0700 (PDT) Message-ID: <60e29e62-4864-4393-b899-01489ee73b91@redhat.com> Date: Thu, 26 Sep 2024 12:48:19 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [syzbot] [mm?] WARNING in copy_huge_pmd To: Peter Xu Cc: syzbot , akpm@linux-foundation.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, jgg@ziepe.ca, leitao@debian.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mingo@redhat.com, rppt@kernel.org, syzkaller-bugs@googlegroups.com, tglx@linutronix.de, x86@kernel.org References: <66f15c8d.050a0220.c23dd.000f.GAE@google.com> <4f96130c-12b7-4afa-ada3-bec354576112@redhat.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: X-Mimecast-Spam-Score: 1 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: C53404001C X-Stat-Signature: 6x6yyhncntbqxaycxp3hyxpsx8dch9gt X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1727347704-996545 X-HE-Meta: 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 K66/0DQq 52Izz6roMuHTMwlAb9riXd+C66if+9sJCocoHledXayKlXhOh4OETvgAsFyXkb7DS9DG+U+VY/h/+IdN5y/6ntuRoSkw3Ny3CpLVvwC7+BLCZEhOac4vm77MP5KGlslxxPFtgimuF30Uz3eRIcBXCBYn1fVxLbG1YHT1uSBVM06CPr16IkrSkOZ15dHYeDBtgPn2EsXnkH4Som7EJr2GLAGGghxTLMUCwx4UzV4oONcWMV0oYGaf7QvJ2jjtnpD1B/25E2LmWzH2NmvFdjyaT4Ze4gnel7Q9ABq5RQdbhMv+1SyhnujUd+KbYSQRjIpSt0CrxKDPAWph/QNCXRxGdU2UJiMoMvBQlXVw5NhJW7P62zgQ7QXoFzulaEvagM9YK9zugZPfe3AT8qh2cCHzow+awBwRmXGas7d2z9urkcsUMKBQt6V+T9HuHgZ1inaNYRjs6JgqlrqkLlyTdxX0JSs2cE1DywhUF+EaQT/FLvMWGiyZiHgqwI7tw3aNOd7LkZr58V4Cg5W6qZMb+UXoQzB+dnwJptIJPvJ4uB0hKBXYdHD0OgltaJPfdQOspQFvprvUmCYnY8EvKMltuHS1e1+VTX6KANpfLZg9tKV4yU8OgrcCXXlIGmv+bSP4HZKBdXRHPwqGLhpK4Hor/KcN/Nk6C5y73QqnoKFXCicYKJsAd2eSs2Dq+ppDkKWvY6tUz5M1WQ5PE0s3N5enqd00YA/ZUFeRSQdZynW/t3agQdClAauKzB1r8JIQBAtXqpAO9zAGFGUI+XZbYp0px6BWAzTwRs04CQ5ouOGK0XGpMYdH4sTk4YjbChhYe26y/JZ+pI/8dMwcGgO6KdReCJ8+CWkygPOiPKv9nSilaLE/xm6Er2VV/NHeiKEWGEOXdkuNy5YYnrNRIu2zU9HApA6HtCowP+zs37nerpC/u3HTsAMTvUY2v5TDKYPin3s8vsfklugHutJ27E32Fmm5v3xAe6eps6Pv5 6j21v35P R9DZJK5jk+lW5zhtZibYKx7bKxjCddTbulMR00ygVjLp6S63cZw1nxIswbVxw0haqrNcIINWw9jGckNGVFIlP2k1MDP465ZmPf5vykKssSc= 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 25.09.24 18:59, Peter Xu wrote: > On Tue, Sep 24, 2024 at 04:45:00PM +0200, David Hildenbrand wrote: >> On 23.09.24 14:18, syzbot wrote: >>> Hello, >>> >>> syzbot found the following issue on: >>> >>> HEAD commit: 88264981f208 Merge tag 'sched_ext-for-6.12' of git://git.k.. >>> git tree: upstream >>> console+strace: https://syzkaller.appspot.com/x/log.txt?x=16c36c27980000 >>> kernel config: https://syzkaller.appspot.com/x/.config?x=e851828834875d6f >>> dashboard link: https://syzkaller.appspot.com/bug?extid=bf2c35fa302ebe3c7471 >>> 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=12773080580000 >>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16ed5e9f980000 >>> >>> Downloadable assets: >>> disk image: https://storage.googleapis.com/syzbot-assets/0e011ac37c93/disk-88264981.raw.xz >>> vmlinux: https://storage.googleapis.com/syzbot-assets/f5c65577e19e/vmlinux-88264981.xz >>> kernel image: https://storage.googleapis.com/syzbot-assets/984d963c8ea1/bzImage-88264981.xz >>> >>> The issue was bisected to: >>> >>> commit 75182022a0439788415b2dd1db3086e07aa506f7 >>> Author: Peter Xu >>> Date: Mon Aug 26 20:43:51 2024 +0000 >>> >>> mm/x86: support large pfn mappings >>> >>> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=17df9c27980000 >>> final oops: https://syzkaller.appspot.com/x/report.txt?x=143f9c27980000 >>> console output: https://syzkaller.appspot.com/x/log.txt?x=103f9c27980000 >>> >>> IMPORTANT: if you fix the issue, please add the following tag to the commit: >>> Reported-by: syzbot+bf2c35fa302ebe3c7471@syzkaller.appspotmail.com >>> Fixes: 75182022a043 ("mm/x86: support large pfn mappings") >>> >>> ------------[ cut here ]------------ >>> WARNING: CPU: 1 PID: 5508 at mm/huge_memory.c:1602 copy_huge_pmd+0x102c/0x1c60 mm/huge_memory.c:1602 >> >> This is the >> >> VM_WARN_ON_ONCE(is_cow_mapping(src_vma->vm_flags) && pmd_write(pmd)) >> >> So we have a special-marked PMD in a COW mapping. >> >> The reproducer seems to involve fuse, but not sure if that makes a >> difference here. > > That chunk of code seems to be there only making sure the test won't get > blocked due to any fused based fs being stuck, via writting to the "abort" > file: > > snprintf(abort, sizeof(abort), "/sys/fs/fuse/connections/%s/abort", > ent->d_name); > int fd = open(abort, O_WRONLY); > if (fd == -1) { > continue; > } > if (write(fd, abort, 1) < 0) { > } > close(fd); > > So far looks not relevant to this issue indeed. > > Unfortunately I cannot reproduce it even with the reproducer. So this one > is a bit tricky.. > > What confuses me yet is how that special bit is set, if it's only used so > far with vfio-pci, and this test doesn't seem to have it involved. > > The test keeps invoking processes, then threads, doing concurrent accesses > over a few stuff (madvise, mremap, migrate_pages, munmap, etc.) on the > pre-mapped areas, but none of them seem to create new memory that can > provide hint on how special bit can start to occur. > > I wonder if some of these operations can race in a way that mm can wrongly > create the special bit (alone with it being writable).. and then it could > be a historical bug, only captured by this patchset due to the newly added > WARN_ON_ONCE somehow, then it could mean that it's not the WRITE bit that > is not intended, but the SPECIAL bit altogether. I assume you are missing a check for present/non-swap pmds. Assume you have a migration entry and end up using the special bit -- which is perfectly fine -- your code would assume it's a present PMD with the special bit set. Maybe for the time being something like: diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 0580ac9e47b9..e55efcad1e6c 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1586,7 +1586,7 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, int ret = -ENOMEM; pmd = pmdp_get_lockless(src_pmd); - if (unlikely(pmd_special(pmd))) { + if (unlikely(pmd_present(pmd) && pmd_special(pmd))) { dst_ptl = pmd_lock(dst_mm, dst_pmd); src_ptl = pmd_lockptr(src_mm, src_pmd); spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING); -- Cheers, David / dhildenb