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 D8D56CCD184 for ; Tue, 21 Oct 2025 09:43:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 41C5F8E0018; Tue, 21 Oct 2025 05:43:14 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3F3938E0002; Tue, 21 Oct 2025 05:43:14 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2E2C78E0018; Tue, 21 Oct 2025 05:43:14 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 1BED78E0002 for ; Tue, 21 Oct 2025 05:43:14 -0400 (EDT) Received: from smtpin29.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id E045814040D for ; Tue, 21 Oct 2025 09:43:13 +0000 (UTC) X-FDA: 84021633066.29.4592BFB Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf13.hostedemail.com (Postfix) with ESMTP id 96DF720003 for ; Tue, 21 Oct 2025 09:43:11 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=g1xABfhx; dmarc=pass (policy=quarantine) header.from=redhat.com; spf=pass (imf13.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1761039791; a=rsa-sha256; cv=none; b=g/xlna6a54JvYbIlAc+vkt+e/HYReGTksZCcQAE/HV0OKA11DRlWf7MbapwmRL1eyoBKrx 5hVt60jxDXWpFiKkahfu06+eZ8o3Qvq2VeGw9T1nDnCA2tQaJvKL5IP+9rAOAMb59gBJbO x6RgDSX2jtzvT+G1ntcyTF7GVAF2eNs= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=g1xABfhx; dmarc=pass (policy=quarantine) header.from=redhat.com; spf=pass (imf13.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=1761039791; 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=7N+UUsWkh/PxB+UVb+bOzD97AQ3e4XfF6EAoBhVIUg4=; b=nG/oySJYmagJOoKtBLkZwji7aDor0aCHmQhol4LEIMOW7hG72a2WonUQ4PUMfMojE/oHcw bfm8o6pNXF+VpXD0hFYEe7Yj5qsGc7yiX+lBkFYwGHrYer1CmqyC9ADpD7eDiigHRau+SD uRO4WIn+ySc9173JtPUGcSEWvwt9NwY= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1761039791; 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=7N+UUsWkh/PxB+UVb+bOzD97AQ3e4XfF6EAoBhVIUg4=; b=g1xABfhxzyrKP6ikXuP1zTqpiX3ePpk3eT7vAUSNSJ49XnTbcpH5Ze6CTMuOx6oG+bleP9 Q3x0eKCRekiuUENgi49tuliILI/nu1W9IRUky5fsGNYCCIWfw8dvNWlEbtu/sjpLRvG3RW Q/UfeYKoZdTwUjPpF+L1W9ySmeSF/Xw= Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-367-IZpDM85kO8qv5NyhcaINYA-1; Tue, 21 Oct 2025 05:43:09 -0400 X-MC-Unique: IZpDM85kO8qv5NyhcaINYA-1 X-Mimecast-MFC-AGG-ID: IZpDM85kO8qv5NyhcaINYA_1761039788 Received: by mail-wr1-f72.google.com with SMTP id ffacd0b85a97d-4270a273b6eso2825083f8f.0 for ; Tue, 21 Oct 2025 02:43:09 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1761039788; x=1761644588; 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=7N+UUsWkh/PxB+UVb+bOzD97AQ3e4XfF6EAoBhVIUg4=; b=eIs/hjiGLO0w1E0icCxfuVwsmPn2AWrY6f63UIIK15uVHb0lgnjkvFtdyHIaN19vkl jFNUgY+qmYLdZ0yd/A7CPAntldXe7OSx0nZKmdjHZC55qetmNW63P/FF820/f3CFebnL yYRFZgDSSpZdKdJwQ3SC9OmCKtTFedpjJ5ceLpjx97SxYOn1eOVlwvNqhx8Y2Tcie05u cwvAyZswDP8SJOUGOUWtlMgK+hhzsyWaJ+xwTr/xUfwmPbVTYwXComQmmYHIVp1PNReL mK9ThP9Q9j1ElljxtSARGXzDhbjZPFmVqYM/RAwDrn+5/qQpRB/2JU5W8SEGfTDOmygx XqvA== X-Forwarded-Encrypted: i=1; AJvYcCX0rexZuRmGOy+WoqnTlWMqQ41zhIIS39XdbReltEHha75iR+ZEZT7UlypLOwKtTfBzAdBDlVS4Tg==@kvack.org X-Gm-Message-State: AOJu0Yyzpk3cUPitMxFXVOoAAgJjYAXpXClBjftTorF6JHZGkc1PvWBn pnGtIR7ikzFYjLmONPdLAOrELNiGaZ/gv/RrFZvPTnnmkV4mKSTaZf+dZaS3rMmswLWv/4xAdhJ Q3sBl/sxD9/JRB1BvAVhZM82i5lzZ1KjLXN4Isp1pZ8LA6WKmWULP X-Gm-Gg: ASbGncsHMo1EXSRgbbvTYCYHihyDtJLhshiFIM4R39JLymmQXzILkiRVt6wmD24vxIQ Pw4DVtBdOacrVF+9SixLqxYv7+ZUZcQJa4JFTYj+it5C/lTRBuV+jJwxsiLITXUFmuybVUTM5Er A7ZTscQHFAvPylCf4IqeNnElN40wUe8iY9XHdeYmLopKgMrPev1IUUKNoocy6oeM9K6hfPEVqWP kPLK573GxqXt/TsUuOdnSchozzs5zsYUUFRTE1rU1l5tv8R3ua/0daRDQeVlMtRIsZOG49wA7hQ UBkMYmI39/wJcPWwDMt4kaI1oIAwp/0D7IQuzItbOAx8A+9GdA5m+gPIC+FQCu+mP7VWt4Jpw8y YkMrQBy3z8M79e9+HjtNb50Beg8ueqgsRMMz2C7F4sZS55zAtaI5mwqRKOI7A3aP9O1moNsOVgl DppkumKZC0rxDU+BS4IeYDt8UgMYQ= X-Received: by 2002:a05:6000:4024:b0:405:3028:1bf2 with SMTP id ffacd0b85a97d-42704e0eeb3mr10685017f8f.62.1761039787951; Tue, 21 Oct 2025 02:43:07 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGKdZ707i2yTNafAh3yeT5ocRi/+Z46tBstB8jxkIB6KoBbNLz4cy9huv2TFyZ6jk4HqWigdQ== X-Received: by 2002:a05:6000:4024:b0:405:3028:1bf2 with SMTP id ffacd0b85a97d-42704e0eeb3mr10684990f8f.62.1761039787436; Tue, 21 Oct 2025 02:43:07 -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-427f00ce3aesm19874869f8f.48.2025.10.21.02.43.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Oct 2025 02:43:06 -0700 (PDT) Message-ID: Date: Tue, 21 Oct 2025 11:43:05 +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: Jan Kara Cc: Christoph Hellwig , 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> <32a9b501-742d-4954-9207-bb7d0c08fccb@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: 3m1ScqK6G5X6n-auiUr-TiyomO9NkdyJbkb5TMZr4xo_1761039788 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-Server: rspam04 X-Rspamd-Queue-Id: 96DF720003 X-Stat-Signature: qf3todejkgnr6zsbpqgq45nn5f97acpi X-HE-Tag: 1761039791-765320 X-HE-Meta: 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 KnEzHxXg A7EcpcuVarzDFi44Y3wLbPVku2BkWpD53TG2sV5tFRLUFgFeQnZ62ul+FFVvOQsYV4ZvbvQ9mXyhl94Z+EjSH0ror3UoJCQg6FoFMcdaA6fwlU29SGWy40qoCpJCq36DleNO4uGFrBfNyfZS7FY0JpmtFpqamZJ3+v6xaQkKKfj5IttoJcq05Dtu2O6SU2d98uVO5qg7SY4X2/xbClKAfalJvpVeWuf00xR0Plu+qGgc/+VfYw5Y6fdWg7bHWqrEvbVIy0YFzBhOatO6B5i8YP4yGJ4t3/y8aJ5oJ8kAbeYzoRgMNyAWaC+o2aQk+Y6JnEXvcZTdx4KvSOtkpzQ49bCKIgtzIFW6g8txGzxP2ZBVlPW86vP9+GOjs8KO1GKJToiGL993NvRPVMOvcZRy3T2EZs2/tL4BpCV/VkKYOTznZfNYygTuXIB02kQ== 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 11:33, Jan Kara wrote: > On Tue 21-10-25 09:57:08, David Hildenbrand wrote: >> 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). > > See some of the cases in my reply to Christoph. It is also stuff like: > > c) Don't allow FOLL_WRITE GUP pins or writeable mapping if there are *any* > pins to the page. > > And we'd have to write-protect the page in the page tables at the moment we > obtain the FOLL_WRITE GUP pin to make sure the pin owner is the only thread > able to modify that page contents while the DIO is running. Oh that's nasty, but yeah I understood the problem now, thanks. -- Cheers David / dhildenb