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[2003:cb:c713:a600:7ca0:23b3:d48a:97c7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-427f93592b6sm113534545e9.3.2024.07.26.02.19.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 26 Jul 2024 02:19:15 -0700 (PDT) Message-ID: <7d88ac63-46b9-4b2e-a46b-c78d8d1d9f0e@redhat.com> Date: Fri, 26 Jul 2024 11:19:15 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 0/2] mm/hugetlb: fix hugetlb vs. core-mm PT locking To: Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Muchun Song , Peter Xu , Oscar Salvador References: <20240725183955.2268884-1-david@redhat.com> <20240725134129.fc9165ac6413c4f774b786c1@linux-foundation.org> 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: <20240725134129.fc9165ac6413c4f774b786c1@linux-foundation.org> 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-Stat-Signature: kpz6pif89j5hp56i4bgf388eyib1mj7e X-Rspamd-Queue-Id: 2070340017 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1721985561-278446 X-HE-Meta: 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 qKFpKOTD EKtB0ZR9zQXynzHhnnKo0riJn37fwaR9w3sS4s+SYGDjbUW56WlloWEF6c3ClFxKuB96X7b/OXtpHnOZbBCzdHr+aSb7rPCrAZOuZhTWLVOT/ThIY4HWMebocHpCx+/GBohHJMhWYWI8ZCakZmrlGsI3rbwHNRLBPr+94uQen/fjy7iPCJ8SEF+UHPsb8ZVnHdH3042bxlxYS0JUlcWAj0+N6SjyqXLPSrwMtB5P9BhqHVpCf0qy1ojOAAHYaOtNaw5XJS55kTOudTTeUzoZd2ZOQazWMWWMFwjwcdcVIKJoVi1PPjeRwVIhUsWrPT9veYYmhUcqnPmx6i9i53m/5yhk4GQnDwS+1U0tw7nYQtLxIb3C5Z/9NueWEIS42jeetyt7hYTHxjYMouuZXuWf9BIaLZ9CFUa7dFFDxs924+Tps6n5sLUeGnHL0KpvHItQB/4ElklVbenEvBoKdWtaaU4GXM4Kv8fWzkkJfPivw9LvnjM0= 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 25.07.24 22:41, Andrew Morton wrote: > On Thu, 25 Jul 2024 20:39:53 +0200 David Hildenbrand wrote: > >> Working on another generic page table walker that tries to avoid >> special-casing hugetlb, I found a page table locking issue with hugetlb >> folios that are not mapped using a single PMD/PUD. >> >> For some hugetlb folio sizes, GUP will take different page table locks >> when walking the page tables than hugetlb when modifying the page tables. >> >> I did not actually try reproducing an issue, but looking at >> follow_pmd_mask() where we might be rereading a PMD value multiple times >> it's rather clear that concurrent modifications are rather unpleasant. >> >> In follow_page_pte() we might be better in that regard -- ptep_get() does >> a READ_ONCE() -- but who knows what else could happen concurrently in >> some weird corner cases (e.g., hugetlb folio getting unmapped and freed). >> >> Did some basic sanity testing with various hugetlb sizes on x86-64 and >> arm64. Maybe I'll find some time to actually write a simple reproducer in >> the common weeks, so this wouldn't have to be all-theoretical for now. > > When can we be confident that this change is merge-worthy? I'm convinced that it is the right thing to do, but I don't think we have to rush this. As Baolin notes, we fixed the same issue in the past, unfortunately also without a reproducer IIUC, so I'll try to reproduce the race, but I'm not 100% sure if I'll manage to do so.. So it's certainly merge-worthy after it had a bit of exposure to -next, but no need to rush this upstream. Thanks! -- Cheers, David / dhildenb