From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id CDB0ACCD184 for ; Tue, 21 Oct 2025 07:57:17 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 30D9F8E0015; Tue, 21 Oct 2025 03:57:17 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2BDFD8E0002; Tue, 21 Oct 2025 03:57:17 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 186028E0015; Tue, 21 Oct 2025 03:57:17 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 02F058E0002 for ; Tue, 21 Oct 2025 03:57:17 -0400 (EDT) Received: from smtpin09.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 9F9CB1403B0 for ; Tue, 21 Oct 2025 07:57:16 +0000 (UTC) X-FDA: 84021366072.09.3F759A4 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf12.hostedemail.com (Postfix) with ESMTP id 26AC940007 for ; Tue, 21 Oct 2025 07:57:13 +0000 (UTC) Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Ayr+HPDm; dmarc=pass (policy=quarantine) header.from=redhat.com; spf=pass (imf12.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1761033434; h=from:from:sender: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:dkim-signature; bh=fUep2F5lenxxRi6fdUvVCk4rNKrfMBfN9N3PQW5oVLs=; b=L6i1/SvbJ6euqCdKWkUQoSObEgrtWjUQMPGOgpSq+UJPcD0+FwLKl1lGekI2buEOLlRTfZ vOw/IzVoj3eyJf5lk188H0hKfLTDWnH0pLeSRitbIbDQ0wiEdr2l//WhO2tTfbQWP97ZTy RCiL6K5bHMWwxlkb3EuTUUnbCStuzCk= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1761033434; a=rsa-sha256; cv=none; b=L0Oiump8IAkB6hO6WyeH7aioK6tTZswVDcg4JykG2Xh5qeqtQIZBIeQ1ElOR2xe6g20VW3 8MNk/ixT8HAaZvPsd2e+qFJI0yjNgoS+iZ8jEd1whdTbhrpyyR2MdNqfbhLtrjL5+MpEnD 3VaFYbxnDyESN25YqVbgianh/kHo73Q= ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Ayr+HPDm; dmarc=pass (policy=quarantine) header.from=redhat.com; spf=pass (imf12.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1761033433; 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=fUep2F5lenxxRi6fdUvVCk4rNKrfMBfN9N3PQW5oVLs=; b=Ayr+HPDmgDXCXU6zQzqozqZBbKq/HGxQA84Wl0T+TergI4cV/IeSmCe2jrR2xUUE34A8oq a7PmXeku6w8lFGbpUA0prhmlMf5qlHaQYP+CZ+GKZBryGEkdMLAC7YYWFo94ZZhgHSEWj5 vjZk6NeAASHH9aR1wp4fkNdEnshdTjA= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-693-gYK7ZIHAO-yw_CAJQw897Q-1; Tue, 21 Oct 2025 03:57:12 -0400 X-MC-Unique: gYK7ZIHAO-yw_CAJQw897Q-1 X-Mimecast-MFC-AGG-ID: gYK7ZIHAO-yw_CAJQw897Q_1761033431 Received: by mail-wr1-f69.google.com with SMTP id ffacd0b85a97d-427015f63faso2715264f8f.0 for ; Tue, 21 Oct 2025 00:57:11 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1761033431; x=1761638231; 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=fUep2F5lenxxRi6fdUvVCk4rNKrfMBfN9N3PQW5oVLs=; b=Hmoz/I2Ldg/He+yXeV9wOzQfLCkaXqMnqEYZZKupg3+J0X9OI5bMBcoDjIzi6oH801 T3V1IwDuXUEfs6k78Zq+v/TALpn1SkOoJNz30bKOX7QjdskES/9PxHZedZZO2kweI57b 7vsR6+45SR9CmsgQ6cYmLK2+zm+d/1RJImjI6deR4JfEGBl7HUL3r84mX/6xfGxrkEVQ p6t6dxCMGNtSK2cIKrrmAli8KNx30mfULaVce/MOSeIy0X8ja2xBEBo45l/NCpe1XRa0 TZMwHC+Qw+r39VfaEThqF5gaziC5lOL70yHpf08YxThO79bHsI2J6acPfFm1u/DbBZTv 2fTA== X-Forwarded-Encrypted: i=1; AJvYcCV7PUO9tIpR3lBaCJqZGB+Lk8N7ErpuW2TmsF7FPy/TBzTS9QQhJE3j691IYTcdrSE3SGAqDZURtA==@kvack.org X-Gm-Message-State: AOJu0Ywugey7FOPE4/I7XhEIn6tiT9QMXzGOXGNUzvSVzslHBZK2CQtG CbhzPf8Tib3MTzT7TpAIAVJmmN7o4pOIrq49+M7RnOGoMmFHFEtSK6K9LnmlwQtekQBC+M8ejD5 NJchnEuEMkHcmSGiMRkApTqEhsuU9Y9IOhTsBaUUYR0K2jT4cHPAm X-Gm-Gg: ASbGncsP1AisxWd8BDPfRbYGs+1DpHCATi541vfyQst8LqM25OlHJfDeuwCnISDGUkz iXq/MTfBFNmm/44gGyqZylSZtoB/QzPepw/QooKbNI6o2mMaWEUlCkyTdwRfVjL1myPHDe4GOAG 2403zGdzzOh44n/01jE9wi9ryhVn6OIsBa18ybcEQEFe229OeQyCQKdAn1J4DdV34DnXtAyt6C4 qzcNKfLdjyyJYw3qv4Q80BW2hZ1NcJ58SdGftfsBVrCcuaqaLngkpNvOZTCiNDscLf1gf7KYigd dtjcI+TnuiYi0El1OoMbhxPCSGWDRSvzkyRevA/IXtTVyjNgP+CGexUvqWGxfzrr2CrNxaToTSk 9mHls8usV+Rlf2/d2MQwRkz0VnfXerlE5sjiRloS2G035SP1DF/Zs9cIRhnOQRv6DpKJSnfIfeB 5PXxdhmDuCfXm3myuHw0jQo3gQhMw= X-Received: by 2002:a05:6000:2507:b0:414:6fe6:8fa1 with SMTP id ffacd0b85a97d-42704d95645mr11202336f8f.38.1761033430879; Tue, 21 Oct 2025 00:57:10 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGBqz1uZsEY1jCmnK5iipnnYUKFUGDAKuTU7UXJ/g7OrVHjIjgtlWv7fVh/TELjD+hkmZZH6Q== X-Received: by 2002:a05:6000:2507:b0:414:6fe6:8fa1 with SMTP id ffacd0b85a97d-42704d95645mr11202325f8f.38.1761033430520; Tue, 21 Oct 2025 00:57:10 -0700 (PDT) Received: from ?IPV6:2003:d8:2f4e:3200:c99d:a38b:3f3a:d4b3? (p200300d82f4e3200c99da38b3f3ad4b3.dip0.t-ipconnect.de. [2003:d8:2f4e:3200:c99d:a38b:3f3a:d4b3]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-427ea5a0f7dsm18728294f8f.4.2025.10.21.00.57.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Oct 2025 00:57:10 -0700 (PDT) Message-ID: <32a9b501-742d-4954-9207-bb7d0c08fccb@redhat.com> Date: Tue, 21 Oct 2025 09:57:08 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: O_DIRECT vs BLK_FEAT_STABLE_WRITES, was Re: [PATCH] btrfs: never trust the bio from direct IO To: Christoph Hellwig Cc: Jan Kara , Matthew Wilcox , Qu Wenruo , linux-btrfs@vger.kernel.org, djwong@kernel.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-mm@kvack.org, martin.petersen@oracle.com, jack@suse.com References: <1ee861df6fbd8bf45ab42154f429a31819294352.1760951886.git.wqu@suse.com> <56o3re2wspflt32t6mrfg66dec4hneuixheroax2lmo2ilcgay@zehhm5yaupav> <5bd1d360-bee0-4fa2-80c8-476519e98b00@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 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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: _5UBEVlqtdMPop7XyqPCSO9EMZjGT8n2jlQOtnSogiA_1761033431 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: rspam01 X-Stat-Signature: s9d5mhkrosi9mkcp3ngzoa8aqwh8zz7i X-Rspam-User: X-Rspamd-Queue-Id: 26AC940007 X-HE-Tag: 1761033433-499347 X-HE-Meta: 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 BcAkQzc0 Pz1+yRcfGixcGPvrsR/LWjBU7ccVmaq/D0kKDqV5UMWTZeHOzpg05/z9Q8B1aFjEovYvOjGCZ2Y6OlFmGnt032PoIoa3p6317SRIxf6HYioOuFoHvQa1t5S27dw/yELIxgd7//KqG+cHG7bQgnb55TVe1IlzzflyZoTTcF1FEa+LC/2SLWOJLNXyIugVPwRO+glQH/5mzyU00o4aRAKMxrhjGde/Z5QLkJpJ372cE/fyjlHYb+zvrL0Jx/AtKDl+m7PoaKPDX7KeDHZdcByIV8u5eQn1daRAE1z6AfZgzbR6GAkQ8gsGCrk/6gS7y2x3VeE+P/QFTobpleAzk/HBGlkFY7E9ozX+WELD98ghoknj2M6E50yxsdsqXmUgyxIvHOa6S4d5NspK7FMjYXVDFSPYIeXT/ox8YSw5+XoBAjeM9tEtOxXkw1f0yS9Nd+5fqa5czqSQw4hj2PghxGdNrlKi+BvfOJP+KICuN 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 21.10.25 09:49, Christoph Hellwig wrote: > On Mon, Oct 20, 2025 at 09:00:50PM +0200, David Hildenbrand wrote: >> Just FYI, because it might be interesting in this context. >> >> For anonymous memory we have this working by only writing the folio out if >> it is completely unmapped and there are no unexpected folio references/pins >> (see pageout()), and only allowing to write to such a folio ("reuse") if >> SWP_STABLE_WRITES is not set (see do_swap_page()). >> >> So once we start writeback the folio has no writable page table mappings >> (unmapped) and no GUP pins. Consequently, when trying to write to it we can >> just fallback to creating a page copy without causing trouble with GUP pins. > > Yeah. But anonymous is the easy case, the pain is direct I/O to file > mappings. Mapping the right answer is to just fail pinning them and fall > back to (dontcache) buffered I/O. Right, I think the rules could likely be a) Don't start writeback to such devices if there may be GUP pins (o writeble PTEs) b) Don't allow FOLL_WRITE GUP pins if there is writeback to such a device Regarding b), I would have thought that GUP would find the PTE to not be writable and consequently trigger a page fault first to make it writable? And I'd have thought that we cannot make such a PTE writable while there is writeback to such a device going on (otherwise the CPU could just cause trouble). -- Cheers David / dhildenb