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=-5.6 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,UNPARSEABLE_RELAY,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 C8CF1C433DB for ; Fri, 5 Feb 2021 07:24:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6D81564FB8 for ; Fri, 5 Feb 2021 07:24:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230489AbhBEHX5 (ORCPT ); Fri, 5 Feb 2021 02:23:57 -0500 Received: from out30-132.freemail.mail.aliyun.com ([115.124.30.132]:52951 "EHLO out30-132.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230486AbhBEHXz (ORCPT ); Fri, 5 Feb 2021 02:23:55 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R291e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04394;MF=haoxu@linux.alibaba.com;NM=1;PH=DS;RN=3;SR=0;TI=SMTPD_---0UNwaEfj_1612509662; Received: from B-25KNML85-0107.local(mailfrom:haoxu@linux.alibaba.com fp:SMTPD_---0UNwaEfj_1612509662) by smtp.aliyun-inc.com(127.0.0.1); Fri, 05 Feb 2021 15:21:03 +0800 Subject: Re: Queston about io_uring_flush To: Pavel Begunkov , io-uring , Jens Axboe References: <63d16aae-1ca7-8939-1c8a-89c600be8462@linux.alibaba.com> <51499dcc-5991-e177-98c4-8cc8a909da70@gmail.com> From: Hao Xu Message-ID: <21456ca2-f5e6-9c93-b42b-697aba82cce7@linux.alibaba.com> Date: Fri, 5 Feb 2021 15:21:02 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <51499dcc-5991-e177-98c4-8cc8a909da70@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org 在 2021/2/4 下午7:00, Pavel Begunkov 写道: > On 04/02/2021 09:31, Hao Xu wrote: >> Hi all, >> Sorry for disturb all of you. Here comes my question. >> When we close a uring file, we go into io_uring_flush(), >> there is codes at the end: >> >> if (!(ctx->flags & IORING_SETUP_SQPOLL) || ctx->sqo_task == current) >>    io_uring_del_task_file(file); >> >> My understanding, this is to delete the ctx(associated with the uring >> file) from current->io_uring->xa. >> I'm thinking of this scenario: the task to close uring file is not the >> one which created the uring file. >> Then it doesn't make sense to delete the uring file from current->io_uring->xa. It should be "delete uring file from >> ctx->sqo_task->io_uring->xa" instead. > > 1. It's not only about created or not, look for > io_uring_add_task_file() call sites. > > 2. io_uring->xa is basically a map from task to used by it urings. > Every user task should clean only its own context (SQPOLL task is > a bit different), it'll be hell bunch of races otherwise. > > 3. If happens that it's closed by a task that has nothing to do > with this ctx, then it won't find anything in its > task->io_uring->xa, and so won't delete anything, and that's ok. > io_uring->xa of sqo_task will be cleaned by sqo_task, either > on another close() or on exit() (see io_uring_files_cancel). > > 4. There is a bunch of cases where that scheme doesn't behave > nice, but at least should not leak/fault when all related tasks > are killed. > Thank you Pavel for the detail explanation. I got it, basically just delay the clean work to sqo_task. I have this question since I'm looking into the tctx->inflight, it puzzles me a little bit. When a task exit(), it finally calls __io_uring_task_cancel(), where we wait until tctx->inflight is 0. What does tctx->inflight actually mean? I thought it stands for all the inflight reqs of ctxs of this task. But in tctx_inflight(): /* * If we have SQPOLL rings, then we need to iterate and find them, and * add the pending count for those. */ xa_for_each(&tctx->xa, index, file) { struct io_ring_ctx *ctx = file->private_data; if (ctx->flags & IORING_SETUP_SQPOLL) { struct io_uring_task *__tctx = ctx->sqo_task->io_uring; inflight += percpu_counter_sum(&__tctx->inflight); } } Why it adds ctx->sqo_task->io_uring->inflight. In a scenario like this: taskA->tctx: ctx0 ctx1 sqpoll normal Since ctx0->sqo_task is taskA, so isn't taskA->io_uring->inflight calculated twice? In another hand, count of requests submited by sqthread will be added to sqthread->io_uring, do we ommit this part？with that being said, should taskA wait for sqes/reqs created by taskA but handled by sqthread?