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=-14.4 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 D1C45C433E0 for ; Thu, 4 Feb 2021 11:17:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 94D4364D9D for ; Thu, 4 Feb 2021 11:17:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235657AbhBDLRR (ORCPT ); Thu, 4 Feb 2021 06:17:17 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39926 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235680AbhBDLPJ (ORCPT ); Thu, 4 Feb 2021 06:15:09 -0500 Received: from mail-wm1-x335.google.com (mail-wm1-x335.google.com [IPv6:2a00:1450:4864:20::335]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DA42EC061788 for ; Thu, 4 Feb 2021 03:14:53 -0800 (PST) Received: by mail-wm1-x335.google.com with SMTP id i9so2655476wmq.1 for ; Thu, 04 Feb 2021 03:14:53 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:autocrypt:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=mcwjGO5Ar/d/uL2JM4ctLnot0SxARJBpoaRveF5ued4=; b=QQ1Ie/K/yAVomos7lzUFwLeBMBSrvO7YFi3dMsnScDzGA1nKPkCJxND7bWLDYHpimD yCEAfu4FE83JdI5+uUhkwqpFs66NfPY4LiWFlV0Iwi+3G9aDQQkUOBxIqLGrw9vMdfMf WYqc8nKDy6xhTEgW3ho2PGUIYTCbs1VMKrw8p8u+2W0rCQnfZ1Np7VRymmlzTiLnn5AJ FOpPWQUZTRRVyBEo1RqOvdFA2YWkIQ1499yYZfalgXA/lJqqjuF1FFUAJUmX9pfJ1ZpL h43dTP0AFJLu4WcZvoqoY9v3LjsX3SEbRT6fXlX2G35XQKPJTKvu3OyOEHYfR21SK6Zu YvSQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:autocrypt :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=mcwjGO5Ar/d/uL2JM4ctLnot0SxARJBpoaRveF5ued4=; b=WO7iHoBQch1/LkFq0tyaJib0UcoD+OSfHVIdEWosAcdiX51YJYJhFgcnTC6Hk6JjrT nyXAjWYUVgzgsDyEqt70nOOKSMRgVvQZ21aY2YMJyyY3oJh0fKph7EX45V11+pTI0xCa Lj4f+RedAFUyHCEaIbx3ppi44fV7MX6/im9wyNWd/b/+ge1orvKwxZxaoTAYlbsBln+k 1SKEif/5D0CjQq6a6FAuyFAz9aIu+FMr0vUe10runyk1rmGaJ8MJZ/+BCreqN/Vxn/u9 5HLRemyngGiQsHWfwb2tTYErvYZXq+YRe3Z+cYhxjfKe1FSAqIrnJyPmMvBF+KxTxiRI 6qug== X-Gm-Message-State: AOAM530TBUfEWjajC33BF6+q4mvAbss7mqO1dDD3jotwvrvhH0DwpI0L Y/jNRv3mek8oxyIYUXQsSBM0ni5nhKAPAg== X-Google-Smtp-Source: ABdhPJxPzT8rRwxR0l8fHrkvnLUIdFTu/wD0RNOOBapk0KTILCh+ciNufUL617pcTEEWG/9wJxsAsA== X-Received: by 2002:a1c:1d8b:: with SMTP id d133mr7096751wmd.172.1612437292614; Thu, 04 Feb 2021 03:14:52 -0800 (PST) Received: from [192.168.8.171] ([148.252.133.145]) by smtp.gmail.com with ESMTPSA id b7sm7500382wru.33.2021.02.04.03.14.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 04 Feb 2021 03:14:52 -0800 (PST) Subject: Re: [PATCH 1/2] io_uring: add uring_lock as an argument to io_sqe_files_unregister() To: Hao Xu , Jens Axboe Cc: io-uring@vger.kernel.org, Joseph Qi References: <1612364276-26847-1-git-send-email-haoxu@linux.alibaba.com> <1612364276-26847-2-git-send-email-haoxu@linux.alibaba.com> <976179ed-6013-3cd7-46a0-aa3201444ac4@gmail.com> 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== Message-ID: <9792fbbb-fa88-a276-9a4a-42fed4426424@gmail.com> Date: Thu, 4 Feb 2021 11:11:07 +0000 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: 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 04/02/2021 03:34, Hao Xu wrote: > 在 2021/2/4 上午12:33, Pavel Begunkov 写道: >> On 03/02/2021 14:57, Hao Xu wrote: >>> io_sqe_files_unregister is currently called from several places: >>>      - syscall io_uring_register (with uring_lock) >>>      - io_ring_ctx_wait_and_kill() (without uring_lock) >>> >>> There is a AA type deadlock in io_sqe_files_unregister(), thus we need >>> to know if we hold uring_lock in io_sqe_files_unregister() to fix the >>> issue. >> >> It's ugly, just take the lock and kill the patch. There can't be any >> contention during io_ring_ctx_free anyway. > Hi Pavel, I don't get it, do you mean this patch isn't needed, and we can just unlock(&uring_lock) before io_run_task_work_sig() and lock(&uring_lock) after it? I knew there won't be contention during io_ring_ctx_free that's why there is no uring_lock in it. > I tried to just do unlock(&uring_lock) before io_run_task_sig() without if(locked) check, it reports something like "there are unpaired mutex lock/unlock" since we cannot just unlock if it's from io_ring_ctx_free. The ugly part is @locked. I know that there is already similar stuff around, but I may go long why and how much I don't like it. io_ring_ctx_free() { ... lock(uring_lock); files_unregister(); unlock(uring_lock); ... } With this you'll always have the mutex locked in unregister, so can drop it unconditionally (if that will ever be needed). It's also cleaner from the synchronisation perspective. >> >>> >>> Signed-off-by: Hao Xu >>> --- >>>   fs/io_uring.c | 10 +++++----- >>>   1 file changed, 5 insertions(+), 5 deletions(-) >>> >>> diff --git a/fs/io_uring.c b/fs/io_uring.c >>> index 38c6cbe1ab38..efb6d02fea6f 100644 >>> --- a/fs/io_uring.c >>> +++ b/fs/io_uring.c >>> @@ -7339,7 +7339,7 @@ static void io_sqe_files_set_node(struct fixed_file_data *file_data, >>>       percpu_ref_get(&file_data->refs); >>>   } >>>   -static int io_sqe_files_unregister(struct io_ring_ctx *ctx) >>> +static int io_sqe_files_unregister(struct io_ring_ctx *ctx, bool locked) >>>   { >>>       struct fixed_file_data *data = ctx->file_data; >>>       struct fixed_file_ref_node *backup_node, *ref_node = NULL; >>> @@ -7872,13 +7872,13 @@ static int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg, >>>         ret = io_sqe_files_scm(ctx); >>>       if (ret) { >>> -        io_sqe_files_unregister(ctx); >>> +        io_sqe_files_unregister(ctx, true); >>>           return ret; >>>       } >>>         ref_node = alloc_fixed_file_ref_node(ctx); >>>       if (!ref_node) { >>> -        io_sqe_files_unregister(ctx); >>> +        io_sqe_files_unregister(ctx, true); >>>           return -ENOMEM; >>>       } >>>   @@ -8682,7 +8682,7 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx) >>>           css_put(ctx->sqo_blkcg_css); >>>   #endif >>>   -    io_sqe_files_unregister(ctx); >>> +    io_sqe_files_unregister(ctx, false); >>>       io_eventfd_unregister(ctx); >>>       io_destroy_buffers(ctx); >>>       idr_destroy(&ctx->personality_idr); >>> @@ -10065,7 +10065,7 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode, >>>           ret = -EINVAL; >>>           if (arg || nr_args) >>>               break; >>> -        ret = io_sqe_files_unregister(ctx); >>> +        ret = io_sqe_files_unregister(ctx, true); >>>           break; >>>       case IORING_REGISTER_FILES_UPDATE: >>>           ret = io_sqe_files_update(ctx, arg, nr_args); >>> >> > -- Pavel Begunkov