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=-10.0 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FORGED_MUA_MOZILLA,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,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 3B690C433DB for ; Sun, 10 Jan 2021 16:52:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 034DA22B2C for ; Sun, 10 Jan 2021 16:52:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726394AbhAJQwC (ORCPT ); Sun, 10 Jan 2021 11:52:02 -0500 Received: from a4-15.smtp-out.eu-west-1.amazonses.com ([54.240.4.15]:57075 "EHLO a4-15.smtp-out.eu-west-1.amazonses.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726265AbhAJQwC (ORCPT ); Sun, 10 Jan 2021 11:52:02 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/simple; s=pqvuhxtqt36lwjpmqkszlz7wxaih4qwj; d=urbackup.org; t=1610297444; h=Subject:To:References:From:Message-ID:Date:MIME-Version:In-Reply-To:Content-Type:Content-Transfer-Encoding; bh=4ZMRTazqJIpZ6htEoopAVyb8N3PexHPg7F41YaHCeKY=; b=CzzuN7Fsuc6MOB9rETP6mNJvJwdlO/c/zguAFuduEMvbPDB7+wHzWKAo0BpJRZZX ZrZsPiJzkpR3pFiWLAUxG3EL3ChkOPqDxtaQr4XNSPBxO7ikkGRjBFXG4IJcwB1Wnkc Ez8l7DiOiLJh90apSg32xlhK9pjtb0HtHo4FTCNk= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/simple; s=shh3fegwg5fppqsuzphvschd53n6ihuv; d=amazonses.com; t=1610297444; h=Subject:To:References:From:Message-ID:Date:MIME-Version:In-Reply-To:Content-Type:Content-Transfer-Encoding:Feedback-ID; bh=4ZMRTazqJIpZ6htEoopAVyb8N3PexHPg7F41YaHCeKY=; b=sEhiMnRfyiutWngBSHq4MpG3PPzuNQXw+aHj6Pg+/BVTiSvfDbH7UyXek4ZMGs6/ vvhXWRgyC8aEbMxv67bW6aCIQ+vsbz0eZGPnogZBHB3T4xuECqD0/v2JveYj6mWJhqL ns7G0TvlRY80WtoUUG7YebNCXn3uOol1Gt3MPQsY= Subject: Re: Fixed buffer have out-dated content To: Pavel Begunkov , Jens Axboe , io-uring@vger.kernel.org References: <01020176e45e6c4d-c15dc1e2-6a6a-407c-a32d-24be51a1b3f8-000000@eu-west-1.amazonses.com> <8ba549a0-7724-a42f-bd11-3605ef0bd034@kernel.dk> <01020176e8159fa5-3f556133-fda7-451b-af78-94c712df611e-000000@eu-west-1.amazonses.com> From: Martin Raiber Message-ID: <01020176ed350725-cc3c8fa7-7771-46c9-8fa9-af433acb2453-000000@eu-west-1.amazonses.com> Date: Sun, 10 Jan 2021 16:50:44 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-SES-Outgoing: 2021.01.10-54.240.4.15 Feedback-ID: 1.eu-west-1.zKMZH6MF2g3oUhhjaE2f3oQ8IBjABPbvixQzV8APwT0=:AmazonSES Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 09.01.2021 21:32 Pavel Begunkov wrote: > On 09/01/2021 16:58, Martin Raiber wrote: >> On 09.01.2021 17:23 Jens Axboe wrote: >>> On 1/8/21 4:39 PM, Martin Raiber wrote: >>>> Hi, >>>> >>>> I have a gnarly issue with io_uring and fixed buffers (fixed >>>> read/write). It seems the contents of those buffers contain old data in >>>> some rare cases under memory pressure after a read/during a write. >>>> >>>> Specifically I use io_uring with fuse and to confirm this is not some >>>> user space issue let fuse print the unique id it adds to each request. >>>> Fuse adds this request data to a pipe, and when the pipe buffer is later >>>> copied to the io_uring fixed buffer it has the id of a fuse request >>>> returned earlier using the same buffer while returning the size of the >>>> new request. Or I set the unique id in the buffer, write it to fuse (via >>>> writing to a pipe, then splicing) and then fuse returns with e.g. >>>> ENOENT, because the unique id is not correct because in kernel it reads >>>> the id of the previous, already completed, request using this buffer. >>>> >>>> To make reproducing this faster running memtester (which mlocks a >>>> configurable amount of memory) with a large amount of user memory every >>>> 30s helps. So it has something to do with swapping? It seems to not >>>> occur if no swap space is active. Problem occurs without warning when >>>> the kernel is build with KASAN and slab debugging. >>>> >>>> If I don't use the _FIXED opcodes (which is easy to do), the problem >>>> does not occur. >>>> >>>> Problem occurs with 5.9.16 and 5.10.5. >>> Can you mention more about what kind of IO you are doing, I'm assuming >>> it's O_DIRECT? I'll see if I can reproduce this. >> It's writing to/reading from pipes (nonblocking, no O_DIRECT). > A blind guess, does it handle short reads and writes? If not, can you > check whether they happen or not? Something like this was what I suspected at first as well. It does check for short read/writes and I added (unnecessary -- because the fuse request structure is 40 bytes and it does io in page sizes) code for retrying short reads at some point. I also checked for the pipes to be empty before they are used at some point and let the kernel log allocation failures (idea was that it was short pipe read/writes because of allocation failure or that something doesn't get rewound properly in this case). Beyond that three things that make a user space problem unlikely:  - occurs only when using fixed buffers and does not occur when running same code without fixed buffer opcodes  - doesn't occur when there is no memory pressure  - I added print(k/f) logging that pointed me in this direction as well >> I can reproduce it with https://github.com/uroni/fuseuring on e.g. a 2GB VPS. Modify bench.sh so that fio loops. Add swap, then run 1400M memtester while it runs (so it swaps, I guess). I can try further reducing the reproducer, but I wanted to avoid that work in case it is something obvious. The next step would be to remove fuse from the equation -- it does try to move the pages from the pipe when splicing to it, for example. >