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[149.14.88.26]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7f4eef7101asm266977985a.38.2025.08.27.02.35.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 27 Aug 2025 02:35:33 -0700 (PDT) Message-ID: <4e148b62-a7c1-4162-a487-1ab0199b774e@redhat.com> Date: Wed, 27 Aug 2025 11:35:30 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] huge_mm.h: is_huge_zero_folio(NULL) should return false To: Andrew Morton , Max Kellermann Cc: lorenzo.stoakes@oracle.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, shikemeng@huaweicloud.com, kasong@tencent.com, nphamcs@gmail.com, bhe@redhat.com, chrisl@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250826231626.218675-1-max.kellermann@ionos.com> <20250826185515.7fbe1821713195b170ac1b31@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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20250826185515.7fbe1821713195b170ac1b31@linux-foundation.org> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: iq30lV6L7I99bboXeGt50OBtChHj3ool6onn9EC7Qo0_1756287335 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 74A0812000A X-Stat-Signature: b5695mt38rtnhkww38ttb3p8p1ukusj3 X-Rspam-User: X-HE-Tag: 1756287337-377642 X-HE-Meta: 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 XlqwONWx 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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 27.08.25 03:55, Andrew Morton wrote: > On Wed, 27 Aug 2025 01:16:24 +0200 Max Kellermann wrote: > >> Calling is_huge_zero_folio(NULL) should not be legal - it makes no >> sense, and a different (theoretical) implementation may dereference >> the pointer. But currently, lacking any explicit documentation, this >> call is legal. >> >> But if somebody really passes NULL, the function should not return >> true - this isn't the huge zero folio after all! However, if the >> `huge_zero_folio` hasn't been allocated yet, it's NULL, and >> is_huge_zero_folio(NULL) just happens to return true, which is a lie. > > Isn't it a bug to call is_huge_zero_folio() before the huge_zero_folio > has been created? It's a bug to call a function that expects a folio without a folio. > > Being a simple soul, I'm thinking > > VM_BUG_ON(!huge_zero_folio); > VM_BUG_ON(!folio); We should just do VM_WARN_ON(!folio); -- Cheers David / dhildenb