From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D0574342CA2 for ; Wed, 27 Aug 2025 09:35:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756287339; cv=none; b=cgHOgwNGM+bOfn3F+xj0UE6J1ZF7L8fzvIQ0a3uRKXMOhDWZaPz1yrJFu6lqt5kll2vm3k8+Z8GshnPnbzGRvwXsRZTIzflDoS97z2mDBf8uJxZZSQXzl1UByn04ORkrTwXgWktiLKM638Rzq6k5B2VYWNiolJ4GYw49QOXGDLU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756287339; c=relaxed/simple; bh=NZyjlx9JVrTus4PAEiK6hrf7n0f1GWNy3/KoGu3XbaM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=mMMO840R8my0p4ma/zDWEHt4cvXh28jMAckLfEBF008Tjw9dFLwKEHAouXTtjinr6/evf0KLS2DwXR9oSJSO49lbGGKkOPH3/T4uCYz6tSXTfE7zLIz2O2Up9pAh6Z8Nm3N/okAN8xnzQDbXHXCKy9oBpR6CeRyaaBRe5nEY/Do= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=EfMEX70+; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="EfMEX70+" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1756287336; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=z5fukYO7kXwNxBLuSBlCYQ0Hv0U0IOhmRPFv+8P4+0E=; b=EfMEX70+i9xsqHqNSLH5STbuETnTfDPmelLEEHcMYmI/FM1Xdbroj+rfD/pZBZ+avt4h4d 64LjevrKlCdwXa7GnmCU9APG5eeMZkvSBav8F74V1Q9NRTZzvR0cBMXKkxSCsMvnIXB59W 8xDP85KQ2tyWUnVc/YSTR8ZpvXdXTPI= Received: from mail-qv1-f70.google.com (mail-qv1-f70.google.com [209.85.219.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-187-9KUxZzOGMvuo9WtxVnQOog-1; Wed, 27 Aug 2025 05:35:35 -0400 X-MC-Unique: 9KUxZzOGMvuo9WtxVnQOog-1 X-Mimecast-MFC-AGG-ID: 9KUxZzOGMvuo9WtxVnQOog_1756287335 Received: by mail-qv1-f70.google.com with SMTP id 6a1803df08f44-70db634fadfso72352786d6.0 for ; Wed, 27 Aug 2025 02:35:35 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1756287335; x=1756892135; h=content-transfer-encoding:in-reply-to:autocrypt:content-language :from:references:cc:to:subject:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=z5fukYO7kXwNxBLuSBlCYQ0Hv0U0IOhmRPFv+8P4+0E=; b=LTp/1w+n3ZzBBNMOY1pu/BiWlvYjTac5fuOwVW7FmarxlPJ/xiKaSPakHFnKm8C63j CXq6eO3Lfyj91JiJ017X5DT5E/EEYvf0x6QES2LLkiOk3hhA3zAU/1WqRJsQnegMqoRN ceaWvEa8QUQcU0SFQ5XYdu2fyGQDclE4cG9n0rIZtN/FHqV8mrGe4M928f/zg9kL6lKI Bwcy3xMPoJ7x6vtZDGGQ+JCPoCoQrnyzNjn9vYpuIfKCRambmUxVh2Msfllf1vrMOt82 WKL3aC3it0hEKc4SYGcD9dLhVl/Nx/3u86tjkU8OwuUXXNJ2KXm9OZYHHqMa6kwZMHqz ADLw== X-Forwarded-Encrypted: i=1; AJvYcCW5eVHWYbPaty9LpALlMIe4pPXV/KxbZv4WXa/BzuWhR8b5j65P/Yg05slRmeHFWa3/g0FPVBPXrytvu44=@vger.kernel.org X-Gm-Message-State: AOJu0Yyvyhc+9qI2NgM5L0EZj4UQr0Go6XzmVyIwfnc2mFDFUmUQBfAo 2JCTEUjJz4r9w05uR3pSuHVl5s4ytazUCCJ+Nxn7NStAGg5V+8hap7v8qOx5A4nVTikKQ66KtvZ v9QF9pNrUK/YpzbXTdPY4xGEmGm8w7VF3sZoeB5FrcJrAQTSbiU7ULcqBD5nmph9mhw== X-Gm-Gg: ASbGncsxR0OzJ6SJGAxVLF+J1s1JkRjrngsjzsqmqAYMWMA0r3wHa/li+/GZ/KSpx34 T2qt2OBd+k8Kr1vWZtohDkOHgrWLwg+oZ1XuENa8yvAmys6C90EKnbFWtOOWYzThFF0rnpzpJAl VT/l8NM2nir0qPhZrbUf3qvm9813gN/5PPXl3/hKHAn4jwGmkezwLjgKXolFZyACFApVNvKDJQi XhoKlCZ2fphdzfFfHyjpn0Wa+Gh/7xk9Weuk4Kgb+6SgALBmvYYcHM8YOv0MBbHW6YCcgQLbv7j M61RYbxGG8MkS8lT8LMArAKV248vRRug+3NFriQ7dTWGo93s90HgB6pIMRxvrw== X-Received: by 2002:a05:620a:1913:b0:7f1:9a91:1dde with SMTP id af79cd13be357-7f19a9144d8mr989207085a.20.1756287334746; Wed, 27 Aug 2025 02:35:34 -0700 (PDT) X-Google-Smtp-Source: AGHT+IE2aVIZceEmeuIaXPM4E0OwdyqHE2I9pakBoXeuwOZHcZ1gpwYn5EvPozgzRW+JuFbVfaucVg== X-Received: by 2002:a05:620a:1913:b0:7f1:9a91:1dde with SMTP id af79cd13be357-7f19a9144d8mr989202885a.20.1756287334240; Wed, 27 Aug 2025 02:35:34 -0700 (PDT) Received: from [10.32.64.156] (nat-pool-muc-t.redhat.com. [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 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: [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 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 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> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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