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[2003:d8:2f09:3f00:d228:bd67:7baa:d604]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-36e4cfee31fsm9640140f8f.47.2024.08.13.02.27.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 13 Aug 2024 02:27:53 -0700 (PDT) Message-ID: <5d7059b0-9e2f-4f50-9316-f2cd63d0d909@redhat.com> Date: Tue, 13 Aug 2024 11:27:52 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] userfaultfd: Don't BUG_ON() if khugepaged yanks our page table To: Jann Horn , Andrew Morton , Pavel Emelyanov , Andrea Arcangeli , Hugh Dickins Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20240812-uffd-thp-flip-fix-v1-0-4fc1db7ccdd0@google.com> <20240812-uffd-thp-flip-fix-v1-2-4fc1db7ccdd0@google.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: <20240812-uffd-thp-flip-fix-v1-2-4fc1db7ccdd0@google.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: rspam12 X-Rspamd-Queue-Id: EFA1410000D X-Stat-Signature: asomcp3gnjudy1ng6n6y37z1amrcqxim X-Rspam-User: X-HE-Tag: 1723541277-194591 X-HE-Meta: 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 9Cvl+UB/ 2KT/X27o+yTskenGYZEcfJINLN6jpT7VO/dMNz1pmVQhsw5iEz2m9szGLzm0AaIwMD6MFgnn82USdRv0MvYA/T/kb10fBH4yyR1MEJTS+X78mptUexQmcB8qL+Ig6Hm5iA8/s8J1E4TLIMgVm9gkrXV41fSURxs8BzVZf4ZcMx+58LbEs+ul1hMDJ30aNWfka/PrO7uOzj/jel/Kny6+++U0KbtPdzTFFC1GbeDkuUSwJPv/tPrV6vvu/OYZk5ZVVJtV1wAu7ONzuEklbLivvnSa5PcGEIZey6LnYSiq7JNewKUMgWnwI0wXkWlw3qThfqm4n44coi/S4Zj2wpuXBwwmzVvl/Ots7JXOPYbC6XUWKJrljlWFU8KXCl/cwsFvPWT3VtNEe7qnKntLptfVNds/YmW6fdwmTmLFSoBK5bV9aXlizoSbn8sf8z1ge5UWscZ5FGFq6dtIkS08mDQ0qHwC82SlxcuhiWO65 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 12.08.24 18:42, Jann Horn wrote: > Since khugepaged was changed to allow retracting page tables in file > mappings without holding the mmap lock, these BUG_ON()s are wrong - get rid > of them. > > We could also remove the preceding "if (unlikely(...))" block, but then > we could reach pte_offset_map_lock() with transhuge pages not just for file > mappings but also for anonymous mappings - which would probably be fine but > I think is not necessarily expected. > > Cc: stable@vger.kernel.org > Fixes: 1d65b771bc08 ("mm/khugepaged: retract_page_tables() without mmap or vma lock") > Signed-off-by: Jann Horn > --- > mm/userfaultfd.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index ec3750467aa5..0dfa97db6feb 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -806,9 +806,10 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, > err = -EFAULT; > break; > } > - > - BUG_ON(pmd_none(*dst_pmd)); > - BUG_ON(pmd_trans_huge(*dst_pmd)); > + /* > + * For shmem mappings, khugepaged is allowed to remove page > + * tables under us; pte_offset_map_lock() will deal with that. > + */ > > err = mfill_atomic_pte(dst_pmd, dst_vma, dst_addr, > src_addr, flags, &folio); > Acked-by: David Hildenbrand -- Cheers, David / dhildenb