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[79.242.53.228]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-428e6e0357asm2331665e9.12.2024.08.01.09.24.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 01 Aug 2024 09:24:54 -0700 (PDT) Message-ID: <8cc5b94c-f861-4ca1-b339-704140ad9255@redhat.com> Date: Thu, 1 Aug 2024 18:24:53 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/hugetlb: fix hugetlb vs. core-mm PT locking To: Peter Xu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, James Houghton , stable@vger.kernel.org, Oscar Salvador , Muchun Song , Baolin Wang References: <20240731122103.382509-1-david@redhat.com> <541f6c23-77ad-4d46-a8ed-fb18c9b635b3@redhat.com> <934885c5-512b-41bf-8501-b568ece34e18@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-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-Queue-Id: 9040118002D X-Rspamd-Server: rspam01 X-Stat-Signature: mj5sb51fdhcohe7ak5yfx7sbtmcmfq4r X-HE-Tag: 1722529500-747799 X-HE-Meta: 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 BLm+Ap1j GoktfFyDBc0SaDx2JQrzSIPrSCTE+ysdLdThidvfdrkAU8+QQIs/NeS6yd9vlu37aVJcd0J4DWiLiQYruP8+PDOdOWkI5Z9EyIaQAUM+cKqEhyH0zvxpE9u3W0tvlpZDt69l5pLjGIm/RnI4I+Ms3nifa36V2t6m1rsDPuVuZ53a7Jlt4YtgHd0E7IUzkaKCfRfablhKc54euX1B6qAMx7oeSJnlpI2TQDCgGvUKJqpxxDhnUXKdx++PZjFvQggO7cJ7gO1Lf+ArSfTRJup7RWOtyPUPMg3K0DnWObghwWmflJ2/iGHEcjZ8EL4hKoLIvrVcYjgNnimcgfFKeQc3lhwvRJARAaMUE02jQXyXhvFwVMP98fWI+eILTrc/nf/ytrXBRiVXNGZNjhaw= 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 01.08.24 18:07, Peter Xu wrote: > On Thu, Aug 01, 2024 at 05:35:20PM +0200, David Hildenbrand wrote: >> Hi Peter, > > [...] > >>>> + else if (size >= PUD_SIZE) >>>> + return pud_lockptr(mm, (pud_t *) pte); >>>> + else if (size >= PMD_SIZE || IS_ENABLED(CONFIG_HIGHPTE)) >>> >>> I thought this HIGHPTE can also be dropped? Because in HIGHPTE it should >>> never have lower-than-PMD huge pages or we're in trouble. That's why I >>> kept one WARN_ON() in my pesudo code but only before trying to take the pte >>> lockptr. >> >> Then the compiler won't optimize out the ptep_lockptr() call and we'll run >> into a build error. And I think the HIGHPTE builderror serves good purpose. >> >> In file included from : >> In function 'ptep_lockptr', >> inlined from 'huge_pte_lockptr' at ./include/linux/hugetlb.h:974:9, >> inlined from 'huge_pte_lock' at ./include/linux/hugetlb.h:1248:8, >> inlined from 'pagemap_scan_hugetlb_entry' at fs/proc/task_mmu.c:2581:8: >> ././include/linux/compiler_types.h:510:45: error: call to '__compiletime_assert_256' declared with attribute error: BUILD_BUG_ON failed: IS_ENABLED(CONFIG_HIGHPTE) >> 510 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) >> | ^ >> ././include/linux/compiler_types.h:491:25: note: in definition of macro '__compiletime_assert' >> 491 | prefix ## suffix(); \ >> | ^~~~~~ >> ././include/linux/compiler_types.h:510:9: note: in expansion of macro '_compiletime_assert' >> 510 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) >> | ^~~~~~~~~~~~~~~~~~~ >> ./include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert' >> 39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg) >> | ^~~~~~~~~~~~~~~~~~ >> ./include/linux/build_bug.h:50:9: note: in expansion of macro 'BUILD_BUG_ON_MSG' >> 50 | BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition) >> | ^~~~~~~~~~~~~~~~ >> ./include/linux/mm.h:2874:9: note: in expansion of macro 'BUILD_BUG_ON' >> 2874 | BUILD_BUG_ON(IS_ENABLED(CONFIG_HIGHPTE)); > > Ahh.. this is in "ifdef USE_SPLIT_PTE_PTLOCKS" section. I'm thinking maybe > we should drop this BUILD_BUG_ON - it says "HIGHPTE shouldn't co-exist with > USE_SPLIT_PTE_PTLOCKS", but I think it can? > > Said that, I think I can also understand your point, where you see > ptep_lockptr() a hugetlb-only function, in that case the BUILD_BUG_ON would > make sense in hugetlb world. > > So.. per my previous nitpick suggestion, IIUC we'll need to drop this > BUILD_BUG_ON, just to say "USE_SPLIT_PTE_PTLOCKS can work with HIGHPTE" and > perhaps slightly more readable; we'll rely on the WARN_ON to guard HIGHPTE > won't use pte lock. I really don't want to drop the BUILD_BUG_ON. The function cannot possibly work with HIGHPTE, especially once used in other context by accident. So I'll leave it like that. Feel free to optimize the hugetlb code further once the fix has landed (e.g., really optimize it out if we cannot possibly have such hugetlb sizes). Thanks! -- Cheers, David / dhildenb