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=-15.1 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 7960BC433EF for ; Fri, 3 Sep 2021 12:28:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 58A0F610A2 for ; Fri, 3 Sep 2021 12:28:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235326AbhICM3U (ORCPT ); Fri, 3 Sep 2021 08:29:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39048 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230005AbhICM3Q (ORCPT ); Fri, 3 Sep 2021 08:29:16 -0400 Received: from mail-wr1-x42a.google.com (mail-wr1-x42a.google.com [IPv6:2a00:1450:4864:20::42a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BCC28C061575 for ; Fri, 3 Sep 2021 05:28:16 -0700 (PDT) Received: by mail-wr1-x42a.google.com with SMTP id b6so7986153wrh.10 for ; Fri, 03 Sep 2021 05:28:16 -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=RZUltNxN8swjKZJxh9uDkp4MdgFsPnFWDUBfK/eqmSs=; b=mg4rjNkDJUb2s4YPFsdsa6XykGehw1WE55/WYzU2wr3rXx7u2ilc/kg8Yzfaqq84oa eVm1uGv1X6kenucMqQIGuG+rMZKufd/+ynSNx0Zaj6QUXIc53tK+K4xeNRFn6mU/dSsX 9QdbLaAquximThuiunX/LzBljGORvJQg/dtF8dD5fi+P6swD6bNKD2BvSfJbzpfXJp7s aOE94war31DrAfjkfMIFEXhv5VuQ41ModpBea7xxGbTdRU7XOLshpDFpDGAxWN9wBq97 tjvs8TdLRwjLOaA+fVvxN+9e6QQS/zWQLKoNhI6k5g6aL5zb7YhaOJ45tbB+O/843xTQ ACEg== 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:subject:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=RZUltNxN8swjKZJxh9uDkp4MdgFsPnFWDUBfK/eqmSs=; b=CH+6czQ7usJDZM0v6Zbv9v6X/5Rt9bkzUAXYwmF89YNjm23V213QlQXn5/TGWSfwxe DD+Yrw7DSgOL7ikdJnZGU4SpF8rNmpQDsm46ohe5ANnBiA/qAKjdrkkgFGwwRZfx2mUf ctD25MrAC/Gmkj8GqEtPomf7nGZi5uB4xnMPzaqVO3zK+JybhkbjU+T8aDWEO+M6dmI9 GuIMU1M/PTNckCJ3puv7blflT1Pp4FXAVTUeqIZVmR/L2nNb00txr7y7EEGf5GkpqIix 51ZVPfwslc+FiU1l1IrSSye5hRKlSa0HbvOIu5/301ZQZwhZK8DOQeTaSDt9zCioS7Hw 2Bdg== X-Gm-Message-State: AOAM532n9j1/jNAMUV4GG7tF+3Kanvwqt4rgg/t13mv4G+HEV4QtCz3z g9ygl6ln6vD61yEg4XoucMw= X-Google-Smtp-Source: ABdhPJyPifUyATsp8PXeSPceVsFzV7Q1lahibnJ7pCn5gDd2oX19rthzpALLV/dHaEdPz5MonJzd6w== X-Received: by 2002:adf:ebcd:: with SMTP id v13mr3842291wrn.400.1630672095368; Fri, 03 Sep 2021 05:28:15 -0700 (PDT) Received: from [192.168.8.197] ([148.252.133.138]) by smtp.gmail.com with ESMTPSA id q13sm4039832wmj.46.2021.09.03.05.28.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 03 Sep 2021 05:28:15 -0700 (PDT) To: Hao Xu , Jens Axboe Cc: io-uring@vger.kernel.org, Joseph Qi References: <20210903110049.132958-1-haoxu@linux.alibaba.com> <20210903110049.132958-2-haoxu@linux.alibaba.com> <302430f6-f83e-4096-448e-9d35f8f4303e@linux.alibaba.com> From: Pavel Begunkov Subject: Re: [PATCH 1/6] io_uring: enhance flush completion logic Message-ID: <5dd28d14-24b5-e2dc-aa55-a68cb5d9f4e8@gmail.com> Date: Fri, 3 Sep 2021 13:27:41 +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: <302430f6-f83e-4096-448e-9d35f8f4303e@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 9/3/21 1:08 PM, Hao Xu wrote: > 在 2021/9/3 下午7:42, Pavel Begunkov 写道: >> On 9/3/21 12:00 PM, Hao Xu wrote: >>> Though currently refcount of a req is always one when we flush inline >> >> It can be refcounted and != 1. E.g. poll requests, or consider > It seems poll requests don't leverage comp cache, do I miss anything? Hmm, looks so. Not great that it doesn't, but probably it's because of trying to submit next reqs right in io_poll_task_func(). I'll be pushing for some changes around tw, with it should be easy to hook poll completion batching with no drawbacks. Would be great if you will be willing to take a shot on it. >> that tw also flushes, and you may have a read that goes to apoll >> and then get tw resubmitted from io_async_task_func(). And other > when it goes to apoll, (say no double wait entry) ref is 1, then read > completes inline and then the only ref is droped by flush. Yep, but some might have double entry. It also will have elevated refs if there was a linked timeout. Another case is io-wq, which takes a reference, and if iowq doesn't put it for a while (e.g. got rescheduled) but requests goes to tw (resubmit, poll, whatever) you have the same picture. >> cases. >> >>> completions, but still a chance there will be exception in the future. >>> Enhance the flush logic to make sure we maintain compl_nr correctly. >> >> See below >> >>> >>> Signed-off-by: Hao Xu >>> --- >>> >>> we need to either removing the if check to claim clearly that the req's >>> refcount is 1 or adding this patch's logic. >>> >>>   fs/io_uring.c | 6 ++++-- >>>   1 file changed, 4 insertions(+), 2 deletions(-) >>> >>> diff --git a/fs/io_uring.c b/fs/io_uring.c >>> index 2bde732a1183..c48d43207f57 100644 >>> --- a/fs/io_uring.c >>> +++ b/fs/io_uring.c >>> @@ -2291,7 +2291,7 @@ static void io_submit_flush_completions(struct io_ring_ctx *ctx) >>>       __must_hold(&ctx->uring_lock) >>>   { >>>       struct io_submit_state *state = &ctx->submit_state; >>> -    int i, nr = state->compl_nr; >>> +    int i, nr = state->compl_nr, remain = 0; >>>       struct req_batch rb; >>>         spin_lock(&ctx->completion_lock); >>> @@ -2311,10 +2311,12 @@ static void io_submit_flush_completions(struct io_ring_ctx *ctx) >>>             if (req_ref_put_and_test(req)) >>>               io_req_free_batch(&rb, req, &ctx->submit_state); >>> +        else >>> +            state->compl_reqs[remain++] = state->compl_reqs[i]; >> >> Our ref is dropped, and something else holds another reference. That >> "something else" is responsible to free the request once it put the last >> reference. This chunk would make the following io_submit_flush_completions() >> to underflow refcount and double free. > True, I see. Thanks Pavel. >> >>>       } >>>         io_req_free_batch_finish(ctx, &rb); >>> -    state->compl_nr = 0; >>> +    state->compl_nr = remain; >>>   } >>>     /* >>> >> > -- Pavel Begunkov