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([2a01:599:929:885b:12c0:a824:1abd:41c4]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4390db1150csm215908075e9.39.2025.02.11.07.15.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 11 Feb 2025 07:15:50 -0800 (PST) Message-ID: <40036244-644a-42e0-a5e4-4838a98b1cbc@redhat.com> Date: Tue, 11 Feb 2025 16:15:48 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 2/4] mm: page_owner: use new iteration API To: Luiz Capitulino , linux-kernel@vger.kernel.org, linux-mm@kvack.org, yuzhao@google.com Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, muchun.song@linux.dev, lcapitulino@gmail.com References: <712c1e058c58ba0d4c407089fbcc45c55ceb8efc.1737754625.git.luizcap@redhat.com> From: David Hildenbrand Content-Language: en-US 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: <712c1e058c58ba0d4c407089fbcc45c55ceb8efc.1737754625.git.luizcap@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 24.01.25 22:37, Luiz Capitulino wrote: > The page_ext_next() function assumes that page extension objects for a > page order allocation always reside in the same memory section, which > may not be true and could lead to crashes. Use the page_ext_iter API > instead. > > Fixes: e98337d11bbd ("mm/contig_alloc: support __GFP_COMP") > Signed-off-by: Luiz Capitulino > --- [...] > void __folio_copy_owner(struct folio *newfolio, struct folio *old) > @@ -364,24 +376,26 @@ void __folio_copy_owner(struct folio *newfolio, struct folio *old) > int i; > struct page_ext *old_ext; > struct page_ext *new_ext; > + struct page_ext_iter old_iter; > + struct page_ext_iter new_iter; > struct page_owner *old_page_owner; > struct page_owner *new_page_owner; > depot_stack_handle_t migrate_handle; > > - old_ext = page_ext_get(&old->page); > + old_ext = page_ext_iter_begin(&old_iter, &old->page); > if (unlikely(!old_ext)) > return; > > - new_ext = page_ext_get(&newfolio->page); > + new_ext = page_ext_iter_begin(&new_iter, &newfolio->page); > if (unlikely(!new_ext)) { > - page_ext_put(old_ext); > + page_ext_iter_end(&old_iter); > return; > } > > old_page_owner = get_page_owner(old_ext); > new_page_owner = get_page_owner(new_ext); > migrate_handle = new_page_owner->handle; > - __update_page_owner_handle(new_ext, old_page_owner->handle, > + __update_page_owner_handle(&new_iter, old_page_owner->handle, > old_page_owner->order, old_page_owner->gfp_mask, > old_page_owner->last_migrate_reason, > old_page_owner->ts_nsec, old_page_owner->pid, > @@ -390,8 +404,13 @@ void __folio_copy_owner(struct folio *newfolio, struct folio *old) > * Do not proactively clear PAGE_EXT_OWNER{_ALLOCATED} bits as the folio > * will be freed after migration. Keep them until then as they may be > * useful. > + * > + * Note that we need to re-grab the page_ext iterator since > + * __update_page_owner_handle changed it. > */ > - __update_page_owner_free_handle(new_ext, 0, old_page_owner->order, > + page_ext_iter_end(&new_iter); > + page_ext_iter_begin(&new_iter, &newfolio->page); So a page_ext_iter_reset() could be helpful, that wouldn't drop the RCU lock. With that, we could probably also drop the comment. > + __update_page_owner_free_handle(&new_iter, 0, old_page_owner->order, > old_page_owner->free_pid, > old_page_owner->free_tgid, > old_page_owner->free_ts_nsec); > @@ -402,12 +421,12 @@ void __folio_copy_owner(struct folio *newfolio, struct folio *old) > */ > for (i = 0; i < (1 << new_page_owner->order); i++) { > old_page_owner->handle = migrate_handle; > - old_ext = page_ext_next(old_ext); > + old_ext = page_ext_iter_next(&old_iter); > old_page_owner = get_page_owner(old_ext); > } > > - page_ext_put(new_ext); > - page_ext_put(old_ext); > + page_ext_iter_end(&new_iter); > + page_ext_iter_end(&old_iter); In general, we should look into implementing the iterator without temporarily dropping the RCU lock I think. Nothing jumped at me from a quick glimpse, but yes, this usage is not that easy. -- Cheers, David / dhildenb