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 X-Spam-Level: X-Spam-Status: No, score=-2.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 028D2C35646 for ; Fri, 21 Feb 2020 18:31:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BEC25206E2 for ; Fri, 21 Feb 2020 18:31:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="R5ysE0Kg" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726393AbgBUSbj (ORCPT ); Fri, 21 Feb 2020 13:31:39 -0500 Received: from mail-wm1-f52.google.com ([209.85.128.52]:36803 "EHLO mail-wm1-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726066AbgBUSbj (ORCPT ); Fri, 21 Feb 2020 13:31:39 -0500 Received: by mail-wm1-f52.google.com with SMTP id p17so2927576wma.1 for ; Fri, 21 Feb 2020 10:31:37 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=to:cc:references:from:autocrypt:subject:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=gT4MuTTV3d23PbgbepB1Ni4n6RPXtmL7nexcKO2jOZE=; b=R5ysE0KgC1oSD8CsKDl8QBzcLLcADld4lOqR2bkQ58LBQO4sHHQLS3me0Og9U4ZkFi ynJZZ8ZoqTXGK2ygML0Do+byXwfTKOfBaXvNjnMNrmbJvJc1vNrx0zJRhJEUDC0b4Qpz frVf/dQOwXQtpOMiJkfjxVsyTsogh74mpl50kE6JI3PqY9bJmmciNuSE0HgEwTaFWrcI jSU6hhN9QHsa9QZa1Sg8+qEK3B7s0VnMvXSfDufNC2a0JtZrKM/EV2/i3Pl6umLGaG8r c5Mt1AXegadPBei2Lmg7SMU3pZ+vSo5DQv8NUOTmTn20DiXHT3FIajHvqQVQOUrojzUJ h7mw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:to:cc:references:from:autocrypt:subject :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=gT4MuTTV3d23PbgbepB1Ni4n6RPXtmL7nexcKO2jOZE=; b=Xmsm6aubaR0HUjEbX5+1UJtV4FK+SUnFvEhT0XsHT4E9Aqrf5N8qi9GKpWR2OnokjA o3PSoDw9r9GZv+hSsmC38EeXXFEro1SvgRuOXQLOxgmd4vtTfAdCA2vPITvz851iRA+c kcwvY6R00oGJYoOIJHuq8iwC+KGud2mzIzLxfaRr8d03gcKtXYB9pArJbW4ss2hc6FJn X8CGO2GTYYdeibdttkUDnQSPFqfgTxaBazlTpv5qXkTm+406SP9RuJpTLE/gHqrE8nrV VpYBHzw0kx3fGJH16d7wtSczHrCDBUkYqaR6+fRANADfRcP+SA+OX4mAhkYFK/5YOuFq aF5Q== X-Gm-Message-State: APjAAAXywqvf1puMOLVFJF1VrPIkYbbniDfgJGjO7UlU7uFmogs3ENta LEtI/QA6AUhK5Q6S2ihXsaN5FSAo X-Google-Smtp-Source: APXvYqyFscDqopyfT+/h7Z0Bd37atk0BtroUcrpT4ajdbHOaKcCWsSRG8YnMYAFALfA/HG/RCT6GoQ== X-Received: by 2002:a05:600c:294:: with SMTP id 20mr5272002wmk.135.1582309896598; Fri, 21 Feb 2020 10:31:36 -0800 (PST) Received: from [192.168.43.74] ([109.126.144.14]) by smtp.gmail.com with ESMTPSA id p26sm4632534wmc.24.2020.02.21.10.31.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 21 Feb 2020 10:31:36 -0800 (PST) To: Jens Axboe , io-uring@vger.kernel.org Cc: glauber@scylladb.com, peterz@infradead.org, Jann Horn References: <20200220203151.18709-1-axboe@kernel.dk> <20200220203151.18709-8-axboe@kernel.dk> <862fb96f-cebe-dfd8-0042-3284985d8704@gmail.com> <3c9a3fca-a780-6d04-65cb-c08ef382a2eb@kernel.dk> From: Pavel Begunkov Autocrypt: addr=asml.silence@gmail.com; prefer-encrypt=mutual; keydata= mQINBFmKBOQBEAC76ZFxLAKpDw0bKQ8CEiYJRGn8MHTUhURL02/7n1t0HkKQx2K1fCXClbps bdwSHrhOWdW61pmfMbDYbTj6ZvGRvhoLWfGkzujB2wjNcbNTXIoOzJEGISHaPf6E2IQx1ik9 6uqVkK1OMb7qRvKH0i7HYP4WJzYbEWVyLiAxUj611mC9tgd73oqZ2pLYzGTqF2j6a/obaqha +hXuWTvpDQXqcOZJXIW43atprH03G1tQs7VwR21Q1eq6Yvy2ESLdc38EqCszBfQRMmKy+cfp W3U9Mb1w0L680pXrONcnlDBCN7/sghGeMHjGKfNANjPc+0hzz3rApPxpoE7HC1uRiwC4et83 CKnncH1l7zgeBT9Oa3qEiBlaa1ZCBqrA4dY+z5fWJYjMpwI1SNp37RtF8fKXbKQg+JuUjAa9 Y6oXeyEvDHMyJYMcinl6xCqCBAXPHnHmawkMMgjr3BBRzODmMr+CPVvnYe7BFYfoajzqzq+h EyXSl3aBf0IDPTqSUrhbmjj5OEOYgRW5p+mdYtY1cXeK8copmd+fd/eTkghok5li58AojCba jRjp7zVOLOjDlpxxiKhuFmpV4yWNh5JJaTbwCRSd04sCcDNlJj+TehTr+o1QiORzc2t+N5iJ NbILft19Izdn8U39T5oWiynqa1qCLgbuFtnYx1HlUq/HvAm+kwARAQABtDFQYXZlbCBCZWd1 bmtvdiAoc2lsZW5jZSkgPGFzbWwuc2lsZW5jZUBnbWFpbC5jb20+iQJOBBMBCAA4FiEE+6Ju PTjTbx479o3OWt5b1Glr+6UFAlmKBOQCGwMFCwkIBwIGFQgJCgsCBBYCAwECHgECF4AACgkQ Wt5b1Glr+6WxZA//QueaKHzgdnOikJ7NA/Vq8FmhRlwgtP0+E+w93kL+ZGLzS/cUCIjn2f4Q Mcutj2Neg0CcYPX3b2nJiKr5Vn0rjJ/suiaOa1h1KzyNTOmxnsqE5fmxOf6C6x+NKE18I5Jy xzLQoktbdDVA7JfB1itt6iWSNoOTVcvFyvfe5ggy6FSCcP+m1RlR58XxVLH+qlAvxxOeEr/e aQfUzrs7gqdSd9zQGEZo0jtuBiB7k98t9y0oC9Jz0PJdvaj1NZUgtXG9pEtww3LdeXP/TkFl HBSxVflzeoFaj4UAuy8+uve7ya/ECNCc8kk0VYaEjoVrzJcYdKP583iRhOLlZA6HEmn/+Gh9 4orG67HNiJlbFiW3whxGizWsrtFNLsSP1YrEReYk9j1SoUHHzsu+ZtNfKuHIhK0sU07G1OPN 2rDLlzUWR9Jc22INAkhVHOogOcc5ajMGhgWcBJMLCoi219HlX69LIDu3Y34uIg9QPZIC2jwr 24W0kxmK6avJr7+n4o8m6sOJvhlumSp5TSNhRiKvAHB1I2JB8Q1yZCIPzx+w1ALxuoWiCdwV M/azguU42R17IuBzK0S3hPjXpEi2sK/k4pEPnHVUv9Cu09HCNnd6BRfFGjo8M9kZvw360gC1 reeMdqGjwQ68o9x0R7NBRrtUOh48TDLXCANAg97wjPoy37dQE7e5Ag0EWYoE5AEQAMWS+aBV IJtCjwtfCOV98NamFpDEjBMrCAfLm7wZlmXy5I6o7nzzCxEw06P2rhzp1hIqkaab1kHySU7g dkpjmQ7Jjlrf6KdMP87mC/Hx4+zgVCkTQCKkIxNE76Ff3O9uTvkWCspSh9J0qPYyCaVta2D1 Sq5HZ8WFcap71iVO1f2/FEHKJNz/YTSOS/W7dxJdXl2eoj3gYX2UZNfoaVv8OXKaWslZlgqN jSg9wsTv1K73AnQKt4fFhscN9YFxhtgD/SQuOldE5Ws4UlJoaFX/yCoJL3ky2kC0WFngzwRF Yo6u/KON/o28yyP+alYRMBrN0Dm60FuVSIFafSqXoJTIjSZ6olbEoT0u17Rag8BxnxryMrgR dkccq272MaSS0eOC9K2rtvxzddohRFPcy/8bkX+t2iukTDz75KSTKO+chce62Xxdg62dpkZX xK+HeDCZ7gRNZvAbDETr6XI63hPKi891GeZqvqQVYR8e+V2725w+H1iv3THiB1tx4L2bXZDI DtMKQ5D2RvCHNdPNcZeldEoJwKoA60yg6tuUquvsLvfCwtrmVI2rL2djYxRfGNmFMrUDN1Xq F3xozA91q3iZd9OYi9G+M/OA01husBdcIzj1hu0aL+MGg4Gqk6XwjoSxVd4YT41kTU7Kk+/I 5/Nf+i88ULt6HanBYcY/+Daeo/XFABEBAAGJAjYEGAEIACAWIQT7om49ONNvHjv2jc5a3lvU aWv7pQUCWYoE5AIbDAAKCRBa3lvUaWv7pfmcEACKTRQ28b1y5ztKuLdLr79+T+LwZKHjX++P 4wKjEOECCcB6KCv3hP+J2GCXDOPZvdg/ZYZafqP68Yy8AZqkfa4qPYHmIdpODtRzZSL48kM8 LRzV8Rl7J3ItvzdBRxf4T/Zseu5U6ELiQdCUkPGsJcPIJkgPjO2ROG/ZtYa9DvnShNWPlp+R uPwPccEQPWO/NP4fJl2zwC6byjljZhW5kxYswGMLBwb5cDUZAisIukyAa8Xshdan6C2RZcNs rB3L7vsg/R8UCehxOH0C+NypG2GqjVejNZsc7bgV49EOVltS+GmGyY+moIzxsuLmT93rqyII 5rSbbcTLe6KBYcs24XEoo49Zm9oDA3jYvNpeYD8rDcnNbuZh9kTgBwFN41JHOPv0W2FEEWqe JsCwQdcOQ56rtezdCJUYmRAt3BsfjN3Jn3N6rpodi4Dkdli8HylM5iq4ooeb5VkQ7UZxbCWt UVMKkOCdFhutRmYp0mbv2e87IK4erwNHQRkHUkzbsuym8RVpAZbLzLPIYK/J3RTErL6Z99N2 m3J6pjwSJY/zNwuFPs9zGEnRO4g0BUbwGdbuvDzaq6/3OJLKohr5eLXNU3JkT+3HezydWm3W OPhauth7W0db74Qd49HXK0xe/aPrK+Cp+kU1HRactyNtF8jZQbhMCC8vMGukZtWaAwpjWiiH bA== Subject: Re: [PATCH 7/9] io_uring: add per-task callback handler Message-ID: Date: Fri, 21 Feb 2020 21:30:52 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: <3c9a3fca-a780-6d04-65cb-c08ef382a2eb@kernel.dk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 21/02/2020 17:50, Jens Axboe wrote: > On 2/21/20 6:51 AM, Pavel Begunkov wrote: >> On 20/02/2020 23:31, Jens Axboe wrote: >>> For poll requests, it's not uncommon to link a read (or write) after >>> the poll to execute immediately after the file is marked as ready. >>> Since the poll completion is called inside the waitqueue wake up handler, >>> we have to punt that linked request to async context. This slows down >>> the processing, and actually means it's faster to not use a link for this >>> use case. >>> >>> We also run into problems if the completion_lock is contended, as we're >>> doing a different lock ordering than the issue side is. Hence we have >>> to do trylock for completion, and if that fails, go async. Poll removal >>> needs to go async as well, for the same reason. >>> >>> eventfd notification needs special case as well, to avoid stack blowing >>> recursion or deadlocks. >>> >>> These are all deficiencies that were inherited from the aio poll >>> implementation, but I think we can do better. When a poll completes, >>> simply queue it up in the task poll list. When the task completes the >>> list, we can run dependent links inline as well. This means we never >>> have to go async, and we can remove a bunch of code associated with >>> that, and optimizations to try and make that run faster. The diffstat >>> speaks for itself. >> >> So, it piggybacks request execution onto a random task, that happens >> to complete a poll. Did I get it right? >> >> I can't find where it setting right mm, creds, etc., or why it have >> them already. > > Not a random task, the very task that initially tried to do the receive > (or whatever the operation may be). Hence there's no need to set > mm/creds/whatever, we're still running in the context of the original > task once we retry the operation after the poll signals readiness. Got it. Then, it may happen in the future after returning from __io_arm_poll_handler() and io_uring_enter(). And by that time io_submit_sqes() should have already restored creds (i.e. personality stuff) on the way back. This might be a problem. BTW, Is it by design, that all requests of a link use personality creds specified in the head's sqe? -- Pavel Begunkov