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=-16.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 3DAB6C433EF for ; Wed, 8 Sep 2021 12:03:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 193FD61131 for ; Wed, 8 Sep 2021 12:03:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349209AbhIHMEr (ORCPT ); Wed, 8 Sep 2021 08:04:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54814 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234758AbhIHMEq (ORCPT ); Wed, 8 Sep 2021 08:04:46 -0400 Received: from mail-wr1-x42b.google.com (mail-wr1-x42b.google.com [IPv6:2a00:1450:4864:20::42b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0CAF8C061575 for ; Wed, 8 Sep 2021 05:03:39 -0700 (PDT) Received: by mail-wr1-x42b.google.com with SMTP id g16so2932882wrb.3 for ; Wed, 08 Sep 2021 05:03:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=to:cc:references:from:subject:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=LRbktXegaJKSVRL9d31bRmsbZtAVR7sG+N4HNv5kDj8=; b=Jlm8SIakVD8LToT05m3/YZH8zv55e4wUJZ/+qqNoMg5pf93S5ZIJE9ixmHa71F96dV a3u6xDtv0ZhrPIUjCFiNPEHhS88SNaF7+z7dmJ82emP/PAJhYG6EtMLKIgdZkF3YR83t bsjJv/Y1V3jDv+deETyRZ0nehFOqr9ud2272l5WoePUU39a1LeCSUJUl73NrcgPvhiTc Meh8XJf4WE0S74mWNAbkyVMywwpiR3WuAlTeRJVsFPK49Usm2RAgV3zPXO5fXM7irhaR iGGS/kBlK2mwQALh5fuq019P9NUS5JkFJLDoUJTRpqsY9G+dBNcsCZTFMet+lvy1vQDd v96g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:to:cc:references:from:subject:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=LRbktXegaJKSVRL9d31bRmsbZtAVR7sG+N4HNv5kDj8=; b=SN5wv3uhpNDejZ9BqNencAvgcSAqoCX+vdfqTNE7IoHZn5xWzvasCh/nNtThIMTFp9 SfUdNWLcqPKhgBOofzEd82E5q1m5+9xmHfJIouAZqRbw047M/olfihtBfU2uno861+1P ix/Gydvm9m4rvCCHNEI0tsZ6k5CuxGYPcPbDhi0WM4I4swee86QDyausFhEXax6cQiEg trfCf9hRqmWCjmAsU0AphnDQjp5Gix1xOh3Qxu+O8KvF4wo/8XzNdPTWTqn09MToQFjs 7bCfObMbj3D+Wd9QOH12dLvHF27p5eWwcGh3Op2ar845eiLIfl5AgJTAFFg3ZCtILQeD YQEA== X-Gm-Message-State: AOAM530E7k2ImWQh1L3lWAPTn/xjSmkF2NTLW/FgVWyfTuKLTwS/ETc+ RjpMdN7fhl1JU1ASQSUHKzQ= X-Google-Smtp-Source: ABdhPJyI8F3rGb8nTooXUgovxYUQJtzwjyKhvLm6/c5YgauQ5mUcFWFg8BbRjjVR2gF7j6iDqCdCUw== X-Received: by 2002:adf:80eb:: with SMTP id 98mr3702455wrl.348.1631102617493; Wed, 08 Sep 2021 05:03:37 -0700 (PDT) Received: from [192.168.8.197] ([185.69.144.232]) by smtp.gmail.com with ESMTPSA id z1sm1854376wmi.34.2021.09.08.05.03.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 08 Sep 2021 05:03:37 -0700 (PDT) To: Hao Xu , Jens Axboe Cc: io-uring@vger.kernel.org, Joseph Qi References: <20210903110049.132958-1-haoxu@linux.alibaba.com> <20210903110049.132958-5-haoxu@linux.alibaba.com> <9a8efd19-a320-29a4-7132-7b5ae5b994ff@gmail.com> <8c052e2a-0ee6-7dac-1169-9d395d2ecad8@linux.alibaba.com> <2ba9fdb5-6d60-21f5-3e20-bc1687c9509f@linux.alibaba.com> From: Pavel Begunkov Subject: Re: [PATCH 4/6] io_uring: let fast poll support multishot Message-ID: Date: Wed, 8 Sep 2021 13:03:04 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <2ba9fdb5-6d60-21f5-3e20-bc1687c9509f@linux.alibaba.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 9/8/21 12:21 PM, Hao Xu wrote: > 在 2021/9/7 下午2:48, Hao Xu 写道: >> 在 2021/9/7 上午3:04, Pavel Begunkov 写道: >>> On 9/3/21 12:00 PM, Hao Xu wrote: >>>> For operations like accept, multishot is a useful feature, since we can >>>> reduce a number of accept sqe. Let's integrate it to fast poll, it may >>>> be good for other operations in the future. >>>> >>>> Signed-off-by: Hao Xu >>>> --- >>>>   fs/io_uring.c | 15 ++++++++++++--- >>>>   1 file changed, 12 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/fs/io_uring.c b/fs/io_uring.c >>>> index d6df60c4cdb9..dae7044e0c24 100644 >>>> --- a/fs/io_uring.c >>>> +++ b/fs/io_uring.c >>>> @@ -5277,8 +5277,15 @@ static void io_async_task_func(struct io_kiocb *req, bool *locked) >>>>           return; >>>>       } >>>> -    hash_del(&req->hash_node); >>>> -    io_poll_remove_double(req); >>>> +    if (READ_ONCE(apoll->poll.canceled)) >>>> +        apoll->poll.events |= EPOLLONESHOT; >>>> +    if (apoll->poll.events & EPOLLONESHOT) { >>>> +        hash_del(&req->hash_node); >>>> +        io_poll_remove_double(req); >>>> +    } else { >>>> +        add_wait_queue(apoll->poll.head, &apoll->poll.wait); >>> >>> It looks like it does both io_req_task_submit() and adding back >>> to the wq, so io_issue_sqe() may be called in parallel with >>> io_async_task_func(). If so, there will be tons of all kind of >>> races. >> IMHO, io_async_task_func() is called in original context one by >> one(except PF_EXITING is set, it is also called in system-wq), so >> shouldn't be parallel case there. > ping... fwiw, the case we're talking about: CPU0 | CPU1 io_async_task_func() | -> add_wait_queue(); | -> io_req_task_submit(); | /* no tw run happened in between */ | io_async_task_func() | --> io_req_task_submit() We called io_req_task_submit() twice without running tw in-between, both of the calls use the same req->io_task_work.node field in the request for accounting, and so the second call will screw tctx->task_list and not only by not considering that req->io_task_work.node is already taken/enqueued. io_req_task_work_add() { wq_list_add_tail(&req->io_task_work.node, &tctx->task_list); } >>> >>>> +    } >>>> + >>>>       spin_unlock(&ctx->completion_lock); >>>>       if (!READ_ONCE(apoll->poll.canceled)) >>>> @@ -5366,7 +5373,7 @@ static int io_arm_poll_handler(struct io_kiocb *req) >>>>       struct io_ring_ctx *ctx = req->ctx; >>>>       struct async_poll *apoll; >>>>       struct io_poll_table ipt; >>>> -    __poll_t ret, mask = EPOLLONESHOT | POLLERR | POLLPRI; >>>> +    __poll_t ret, mask = POLLERR | POLLPRI; >>>>       int rw; >>>>       if (!req->file || !file_can_poll(req->file)) >>>> @@ -5388,6 +5395,8 @@ static int io_arm_poll_handler(struct io_kiocb *req) >>>>           rw = WRITE; >>>>           mask |= POLLOUT | POLLWRNORM; >>>>       } >>>> +    if (!(req->flags & REQ_F_APOLL_MULTISHOT)) >>>> +        mask |= EPOLLONESHOT; >>>>       /* if we can't nonblock try, then no point in arming a poll handler */ >>>>       if (!io_file_supports_nowait(req, rw)) >>>> >>> > -- Pavel Begunkov