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=-8.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,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 EFD2DC433E2 for ; Wed, 9 Sep 2020 13:10:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A1492215A4 for ; Wed, 9 Sep 2020 13:10:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20150623.gappssmtp.com header.i=@kernel-dk.20150623.gappssmtp.com header.b="1fqoKCS9" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730306AbgIINKS (ORCPT ); Wed, 9 Sep 2020 09:10:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53848 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730288AbgIINKK (ORCPT ); Wed, 9 Sep 2020 09:10:10 -0400 Received: from mail-il1-x141.google.com (mail-il1-x141.google.com [IPv6:2607:f8b0:4864:20::141]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 02605C061573 for ; Wed, 9 Sep 2020 06:10:16 -0700 (PDT) Received: by mail-il1-x141.google.com with SMTP id b17so2255152ilh.4 for ; Wed, 09 Sep 2020 06:10:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:content-language:content-transfer-encoding; bh=JIwMMJvy8NSR72GjBzf/1/n1e32e3HoQ0TG7hZ1Z8iY=; b=1fqoKCS93zomLAPLYFvtAADRsHANxVXZwhlJs4tKEkEQ6NgNLNx44zLMvPqRizkaB/ b353JlemoegUZRgbeuZgIdY70GYzGeNYmhouqB014tqkp81r2xPaGP4WISGueCic1R/x Gyts3eWmogG8gT4sJhrTfZHMxmeUIGhevruSBQ00BXbP+D5vZxmARtbeitKoV+wPAOfJ bQJ3QlU89dGcOtoySKm1UF+dYaPEelrsUZFlQYpoRKRfMAwU+HRsOZ4OaP1Ca7pXkgWY 6zLhclNIMuaKzIHe3thwgUtkW40osedNEdl0985S5lBwtEVbUtpz1jLgFMCg4BmMr3DG AKwA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=JIwMMJvy8NSR72GjBzf/1/n1e32e3HoQ0TG7hZ1Z8iY=; b=PAXJgwkHr0zV3ZNXa2JIsq2cP3olvRjkAw+yO34JojQFHqzLEv4TrpV1nNen2rInVk n1WHWOtEK2ewaW6rrSeAIVMz0tW12k1SsJy6RgpiI7zf3hsHZ2wNDi2rE9T8aqrs7UO4 x4v0JXElZBpjyNPlXL3zLC4XW5HuHxmwwntJbMQaKUhtREgpnCj+2v/8jAVilSPaSASU IBLo3I5cidX3gR/J3B7HT6a+XBZWB/6HWMKR2u90Rxxq2cjMwLYjfE5YHBPdKM5g2g8o 3bcpOF7gGfhisZNcMS9P1yHtnu1N3G4jd9MbxcNuBU2pjX+LQXlejiW4537v2AwiYPjJ vBrg== X-Gm-Message-State: AOAM53343cT9cCF8MqhaB2DwHFxJTEAutoUX0Ko4zI0a8zPUK/SY1ztO frZc7vDcgoMOMUlT1upRtqicXhfpp3iX7ita X-Google-Smtp-Source: ABdhPJzbEeD9ds27pvC9J/pkP6BaSGrAh+j7vhjgy/O+QrbmWJMvj2AzjOp44FvsnATm1GRiKcAMDA== X-Received: by 2002:a92:9986:: with SMTP id t6mr3565849ilk.28.1599657014332; Wed, 09 Sep 2020 06:10:14 -0700 (PDT) Received: from [192.168.1.10] ([65.144.74.34]) by smtp.gmail.com with ESMTPSA id c12sm1337000ilm.17.2020.09.09.06.10.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 09 Sep 2020 06:10:12 -0700 (PDT) Subject: Re: [PATCH for-next] io_uring: ensure IOSQE_ASYNC file table grabbing works, with SQPOLL To: Pavel Begunkov , io-uring References: <8f6871c4-1344-8556-25a7-5c875aebe4a5@gmail.com> <622649c5-e30d-bc3c-4709-bbe60729cca1@kernel.dk> <1c088b17-53bb-0d6d-6573-a1958db88426@kernel.dk> <801ed334-54ea-bdee-4d81-34b7e358b506@gmail.com> From: Jens Axboe Message-ID: <370c055e-fa8d-0b80-bd34-ba3ba9bc6b37@kernel.dk> Date: Wed, 9 Sep 2020 07:10:12 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <801ed334-54ea-bdee-4d81-34b7e358b506@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 9/9/20 1:09 AM, Pavel Begunkov wrote: > On 09/09/2020 01:54, Jens Axboe wrote: >> On 9/8/20 3:22 PM, Jens Axboe wrote: >>> On 9/8/20 2:58 PM, Pavel Begunkov wrote: >>>> On 08/09/2020 20:48, Jens Axboe wrote: >>>>> Fd instantiating commands like IORING_OP_ACCEPT now work with SQPOLL, but >>>>> we have an error in grabbing that if IOSQE_ASYNC is set. Ensure we assign >>>>> the ring fd/file appropriately so we can defer grab them. >>>> >>>> IIRC, for fcheck() in io_grab_files() to work it should be under fdget(), >>>> that isn't the case with SQPOLL threads. Am I mistaken? >>>> >>>> And it looks strange that the following snippet will effectively disable >>>> such requests. >>>> >>>> fd = dup(ring_fd) >>>> close(ring_fd) >>>> ring_fd = fd >>> >>> Not disagreeing with that, I think my initial posting made it clear >>> it was a hack. Just piled it in there for easier testing in terms >>> of functionality. >>> >>> But the next question is how to do this right...> >> Looking at this a bit more, and I don't necessarily think there's a >> better option. If you dup+close, then it just won't work. We have no >> way of knowing if the 'fd' changed, but we can detect if it was closed >> and then we'll end up just EBADF'ing the requests. >> >> So right now the answer is that we can support this just fine with >> SQPOLL, but you better not dup and close the original fd. Which is not >> ideal, but better than NOT being able to support it. >> >> Only other option I see is to to provide an io_uring_register() >> command to update the fd/file associated with it. Which may be useful, >> it allows a process to indeed to this, if it absolutely has to. > > Let's put aside such dirty hacks, at least until someone actually > needs it. Ideally, for many reasons I'd prefer to get rid of BUt it is actually needed, otherwise we're even more in a limbo state of "SQPOLL works for most things now, just not all". And this isn't that hard to make right - on the flush() side, we just need to park/stall the thread and clear the ring_fd/ring_file, then mark the ring as needing a queue enter. On the queue enter, we re-set the fd/file if they're NULL, unpark/unstall the thread. That's it. I'll write this up and test it. > fcheck(ctx->ring_fd) in favour of synchronisation in io_grab_files(), > but I wish I knew how. That'd be nice, and apply equally to all cases as the SQPOLL case isn't special at all anymore. -- Jens Axboe