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[2003:d8:2f31:700:3851:c66a:b6b9:3490]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a568a60d0fsm13622090f8f.22.2025.06.17.05.08.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Jun 2025 05:08:17 -0700 (PDT) Message-ID: <3eb8e1e2-5887-47ed-addc-3be664dd7053@redhat.com> Date: Tue, 17 Jun 2025 14:08:16 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/5] mm,hugetlb: Document the reason to lock the folio in the faulting path To: Oscar Salvador Cc: Andrew Morton , Muchun Song , James Houghton , Peter Xu , Gavin Guo , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <44f0f1cc-307a-46e3-9e73-8b2061e4e938@redhat.com> <1297fdd5-3de2-45bc-b146-e14061643fee@redhat.com> <11a1d0f7-ef4e-4836-9bde-d7651eebcd03@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: 0 X-Mimecast-MFC-PROC-ID: bAvf7Us6gAoKza07P1boKxizYO1gEHKNr0pGodWxrlE_1750162098 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: DC2CFA000F X-Stat-Signature: fq1h7s5qeoozb3uzjw9zwttsfbis6gju X-HE-Tag: 1750162105-395090 X-HE-Meta: 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 uWf6cN1/ 8uSKUHaEPjyk6OVdtUEgcKMhqm6UpsPOBQnMq5n6kXLWjW7K8uhJADEkloMitrKF9EuBJtlIKNfIJLOORUYUOKL4YtgNlOlG9CqN4Bc7TNcC98YVGgvAUtY4Jnpu51JEmNIJCgxtJ20VFx1HY+1vKEoEYBbgT/SeHD+dE/nILn82o/gPlu84IPPJ9zu3N5i4btB1cD2pHJQOw+DUvJEwL4B2vNRAQS8KG1reNnQ503FWY45Ve54GpHgu3NcuCpnzcp04J53VsbfrfoqphEqtVzJmtvAH0BPvpFzXLQEqG+KXzIJPdMhOldWlh/jXM6Bnh2PY/nwY3oCcutzoC3rbyZdT/kiXCgLIKbIQRuozdLBrtDG9DeEWXTiueMJm0+3VNxk/EoVXq0VWQx8T//r9JOL8bthqTuXLl3xeRIQoIEjINfbqJILwJebsWqA== 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 17.06.25 14:04, Oscar Salvador wrote: > On Tue, Jun 17, 2025 at 01:27:18PM +0200, David Hildenbrand wrote: >>> @@ -6198,6 +6198,8 @@ static vm_fault_t hugetlb_wp(struct vm_fault *vmf) >>> * in scenarios that used to work. As a side effect, there can still >>> * be leaks between processes, for example, with FOLL_GET users. >>> */ >>> + if (folio_test_anon(old_folio)) >>> + folio_lock(old_folio); >> >> If holding the PTL, this would not work. You'd have to unlock PTL, lock >> folio, retake PTL, check pte_same. > > Why so? > > hugetlb_no_page() has already checked pte_same under PTL, then mapped the page > and called hugetlb_wp(). > > hugetlb_no_page > vmf->ptl = huge_pte_lock() > pte_same > set_huge_pte_at > hugetlb_wp > > and in hugetlb_wp() we're still holding the PTL. > Why do we have to release PTL in order to lock the folio? > This folio can't have been unmapped because we're holding PTL, right? > And it can't have been truncaed for the same reason. > > It's because some lock-order issue? folio lock is a sleeping lock, PTL is a spinlock. :) -- Cheers, David / dhildenb