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[2003:cb:c715:a000:40d8:86b1:96c0:9382]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-37cd564d2c7sm4332934f8f.9.2024.09.28.01.39.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 28 Sep 2024 01:39:07 -0700 (PDT) Message-ID: Date: Sat, 28 Sep 2024 10:39:06 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/5] mm: memory_hotplug: remove head variable in do_migrate_range() From: David Hildenbrand To: Matthew Wilcox , Kefeng Wang Cc: Andrew Morton , Oscar Salvador , Miaohe Lin , Naoya Horiguchi , linux-mm@kvack.org, dan.carpenter@linaro.org, Jonathan Cameron References: <20240827114728.3212578-1-wangkefeng.wang@huawei.com> <20240827114728.3212578-2-wangkefeng.wang@huawei.com> <20a75b57-12a6-468f-bd7c-0aeb2f259228@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: <20a75b57-12a6-468f-bd7c-0aeb2f259228@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-Stat-Signature: eomcpfmmewqfifdi98dhz69xtxxtwriz X-Rspamd-Queue-Id: D170B140008 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1727512751-843247 X-HE-Meta: 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 9R3av2W5 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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 28.09.24 10:34, David Hildenbrand wrote: > On 28.09.24 06:55, Matthew Wilcox wrote: >> On Tue, Aug 27, 2024 at 07:47:24PM +0800, Kefeng Wang wrote: >>> Directly use a folio for HugeTLB and THP when calculate the next pfn, then >>> remove unused head variable. >> >> I just noticed this got merged. You're going to hit BUG_ON with it. >> >>> - if (PageHuge(page)) { >>> - pfn = page_to_pfn(head) + compound_nr(head) - 1; >>> - isolate_hugetlb(folio, &source); >>> - continue; >>> - } else if (PageTransHuge(page)) >>> - pfn = page_to_pfn(head) + thp_nr_pages(page) - 1; >>> + /* >>> + * No reference or lock is held on the folio, so it might >>> + * be modified concurrently (e.g. split). As such, >>> + * folio_nr_pages() may read garbage. This is fine as the outer >>> + * loop will revisit the split folio later. >>> + */ >>> + if (folio_test_large(folio)) { >> >> But it's not fine. Look at the implementation of folio_test_large(): >> >> static inline bool folio_test_large(const struct folio *folio) >> { >> return folio_test_head(folio); >> } >> >> That's going to be provided by: >> >> #define FOLIO_TEST_FLAG(name, page) \ >> static __always_inline bool folio_test_##name(const struct folio *folio) \ >> { return test_bit(PG_##name, const_folio_flags(folio, page)); } >> >> and here's the BUG: >> >> static const unsigned long *const_folio_flags(const struct folio *folio, >> unsigned n) >> { >> const struct page *page = &folio->page; >> >> VM_BUG_ON_PGFLAGS(PageTail(page), page); >> VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags), page); >> return &page[n].flags; >> } >> >> (this page can be transformed from a head page to a tail page because, >> as the comment notes, we don't hold a reference. >> >> Please back this out. > > Should we generalize the approach in dump_folio() to locally copy a > folio, so we can safely perform checks before deciding whether we want > to try grabbing a reference on the real folio (if it's still a folio :) )? > Oh, and I forgot: isn't the existing code already racy? PageTransHuge() -> VM_BUG_ON_PAGE(PageTail(page), page); -- Cheers, David / dhildenb