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Thu, 11 Jul 2024 14:45:55 -0700 (PDT) Message-ID: <3879ee72-84de-4d2a-93a8-c0b3dc3f0a4c@redhat.com> Date: Thu, 11 Jul 2024 23:45:54 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: Fix mmap_assert_locked() in follow_pte() From: David Hildenbrand To: Pei Li , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, skhan@linuxfoundation.org, syzkaller-bugs@googlegroups.com, linux-kernel-mentees@lists.linuxfoundation.org, syzbot+35a4414f6e247f515443@syzkaller.appspotmail.com, Peter Xu References: <20240710-bug12-v1-1-0e5440f9b8d3@gmail.com> <92a2dc30-6e48-44ea-9cde-693b911f200d@redhat.com> 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: <92a2dc30-6e48-44ea-9cde-693b911f200d@redhat.com> X-Mimecast-Spam-Score: 0 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-Rspam-User: X-Rspamd-Queue-Id: 86E6D20003 X-Stat-Signature: btczyjw31bp6czhk3jxp3u6ywcz418j1 X-HE-Tag: 1720734367-579200 X-HE-Meta: U2FsdGVkX1+WL2e3ofA8OyGGDDX/4YT7Sk3Vz9g6X7Cxk7626A3UYdNM56ikLnD/eUCmFNP3kn4HPMWYBXj9lpJySeqP5bAgDT3RG/yOJgRfyDl32SZ6uxtBMbOsM5PmRTnn2zZiVWjDWAcI4XKVmwX6gtyWcfnb8D3bj8vSpDkJjV3nJeaxOhypPjdHFx6/ehNf2jEPY7/8AUHPmVPi0xP6FZM9hjxSf2xbRC5HBOCkt//mbanv+HJy2z1IIU/GCM5w01jjuOOISH8dj1XolhM8gdbMWgr1K5evdp3mZHzszBuVCsWUJxcb6MNcbVEamGodY+OsKEcu7c8sOBU2x526+0wXhBu3wkcUzNw19X6jPaNY7YCYxroF1qfl79YIkzjj3V5UZmkFGUqshx00MlgTil3/QM59qU+e3iyVbcitcy3Iu8BkeAiUlUUEBGRWWYuNpk5JKi7auoNmLvk3WwcnI2SQxa6sd8pzUv4EJpP0WtDAhHPUoLXiZrtJvt3WEm3vtKC+UVtrCMAcSWrrvpRDFAH6EDa9hu/pICK9dxUYqnu64H/Inc8thlQMRqRC8x4vYuhwUPH11v4Q4dvjujOM1gS9c8zyNGGq2k7FHT4iP19DI9rAlCOKEdJk6NjqE2a258uLq+9QE1i8Wzz6SL8thrHgnS0HTUhpsk7UlE1czWK5xA0or3O9Qk5KN8Yp4G26qHfdLyBHwu2HNAoMJ2H9VoGHtkx2Ykm+d827b8bTM5ILCmPDwoOtVTkIj0PSmrEkQMMOaD0zE7929qF0oGkLX5tL+6UVBZ2s+AwxR7zdv7QOIE9ljmHZafcGuD0/ndaykyAdxf60C6zs5r5pG9rESZH4QsWgeigPmNWpTuD1z6OZPz8Gyjp5gShXPYshTAgGJQih/bz8IpHfAO7k9HQ5RP+CjqWHU5Vzjey9J6IIwl5eSQxlT536nCU4SbHM/eEJQQJcw5+VONp7KQ3 iB4BHA6W 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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 11.07.24 23:33, David Hildenbrand wrote: > On 11.07.24 07:13, Pei Li wrote: >> This patch fixes this warning by acquiring read lock before entering >> untrack_pfn() while write lock is not held. >> >> syzbot has tested the proposed patch and the reproducer did not >> trigger any issue. >> >> Reported-by: syzbot+35a4414f6e247f515443@syzkaller.appspotmail.com >> Closes: https://syzkaller.appspot.com/bug?extid=35a4414f6e247f515443 >> Tested-by: syzbot+35a4414f6e247f515443@syzkaller.appspotmail.com >> Signed-off-by: Pei Li >> --- >> Syzbot reported the following warning in follow_pte(): >> >> WARNING: CPU: 3 PID: 5192 at include/linux/rwsem.h:195 rwsem_assert_held include/linux/rwsem.h:195 [inline] >> WARNING: CPU: 3 PID: 5192 at include/linux/rwsem.h:195 mmap_assert_locked include/linux/mmap_lock.h:65 [inline] >> WARNING: CPU: 3 PID: 5192 at include/linux/rwsem.h:195 follow_pte+0x414/0x4c0 mm/memory.c:5980 >> >> This is because we are assuming that mm->mmap_lock should be held when >> entering follow_pte(). This is added in commit c5541ba378e3 (mm: >> follow_pte() improvements). >> >> However, in the following call stack, we are not acquring the lock: >> follow_phys arch/x86/mm/pat/memtype.c:957 [inline] >> get_pat_info+0xf2/0x510 arch/x86/mm/pat/memtype.c:991 >> untrack_pfn+0xf7/0x4d0 arch/x86/mm/pat/memtype.c:1104 >> unmap_single_vma+0x1bd/0x2b0 mm/memory.c:1819 >> zap_page_range_single+0x326/0x560 mm/memory.c:1920 > > That implies that unmap_vmas() is called without the mmap lock in read > mode, correct? > > Do we know how this happens? > > * exit_mmap() holds the mmap lock in read mode > * unmap_region is documented to hold the mmap lock in read mode I think this is it (missed the call from zap_page_range_single()): follow_phys arch/x86/mm/pat/memtype.c:957 [inline] get_pat_info+0xf2/0x510 arch/x86/mm/pat/memtype.c:991 untrack_pfn+0xf7/0x4d0 arch/x86/mm/pat/memtype.c:1104 unmap_single_vma+0x1bd/0x2b0 mm/memory.c:1819 zap_page_range_single+0x326/0x560 mm/memory.c:1920 unmap_mapping_range_vma mm/memory.c:3684 [inline] unmap_mapping_range_tree mm/memory.c:3701 [inline] unmap_mapping_pages mm/memory.c:3767 [inline] unmap_mapping_range+0x1ee/0x280 mm/memory.c:3804 truncate_pagecache+0x53/0x90 mm/truncate.c:731 simple_setattr+0xf2/0x120 fs/libfs.c:886 notify_change+0xec6/0x11f0 fs/attr.c:499 do_truncate+0x15c/0x220 fs/open.c:65 handle_truncate fs/namei.c:3308 [inline] I think Peter recently questioned whether untrack_pfn() should be even called from the place, but I might misremember things. Fix should work (I suspect we are not violating some locking rules?), PFNMAP should not happen there too often that we really care. If everything fails, we could drop the assert, but I'm hoping we can avoid that. We really want most users of follow_pte() to do the right thing. -- Cheers, David / dhildenb