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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B604EC433F5 for ; Mon, 16 May 2022 19:14:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343531AbiEPTO0 (ORCPT ); Mon, 16 May 2022 15:14:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37730 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244902AbiEPTOZ (ORCPT ); Mon, 16 May 2022 15:14:25 -0400 Received: from mail-io1-xd33.google.com (mail-io1-xd33.google.com [IPv6:2607:f8b0:4864:20::d33]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 41DC239164 for ; Mon, 16 May 2022 12:14:23 -0700 (PDT) Received: by mail-io1-xd33.google.com with SMTP id y12so8683527ior.7 for ; Mon, 16 May 2022 12:14:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20210112.gappssmtp.com; s=20210112; h=message-id:date:mime-version:user-agent:subject:content-language:to :cc:references:from:in-reply-to:content-transfer-encoding; bh=yu8jpBcESlRO41WVtwunoeenHnb5B2EXEF8tRgSzHgE=; b=tqCZDZ0dx3cF6RCC1hPbCmSnLFGA3LUJA9FPT9yl/mq42q/ABuK1f4ejnoMS+6ky5L sZV492OnuqI4ApfBjNxD/my1zZ8AwFpREQ1L/GBEJ32+4I6LJOEjUl2OgZalqTspT+p+ 2mNM7tW92wIo49NXj9jlQ35oPO2uzhro/D/D0tz2/GPSuepEvmI3a9TXF0pwkODrPVxD Z9XoZjpMtFeR0EceB3XQFrrJPstyipKo6XN44acrdN7iQWOBUT6EbQ3duotSqKjd1XR3 sSGEgWF7gL//m1iuVAY1+gkUbrNLBBX8g9luU4HxxMQUlozNuKRnPvzYT56wXGLm7anM QWJw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=yu8jpBcESlRO41WVtwunoeenHnb5B2EXEF8tRgSzHgE=; b=Q3AuWncsYcFMRXkr9fUASHU5YL3kFsnNe7rXgOGHS4LpW3bNNYROLSexF5QZkw+xPV 9lZ+HCh6cEhkiGDyKUv5BhjltefwAWZFOcgJUq0IS25iffLqPM0TxONE8+99hKLfeefH OdNM1nrcUs9YqvQ1KfrX65p2E7jK83qdTsDkcT8hfeLC9zccR+zCOylhYvzpXnSQ7dCC 2Rjd+FYVNnum31GWjJGj3Ia7yyRUINBM3dwNQGtUhYsUK8IfBG97Pf5x0AVt2MEd8yC/ SZ+qEuGRCXWoICudAhVy7jz7wmrMvBtCIrRFkyFihqqp3Viv0vHdnazp3usDvfBD9VOa WT5g== X-Gm-Message-State: AOAM5318bTmpiPjozsWmBbRYZW74rONHTF7X4BzA1ARmlkLSFJ/H3DeD GgqmG2tZBuxbGc9a5j0sfO+EmA== X-Google-Smtp-Source: ABdhPJzXFsXpsavDxnMRAYebmJL6UV04urGytrVKDDgSBJcwMy3VAVKN7/BgDEhXPwIkvfb4FKH84Q== X-Received: by 2002:a02:7a06:0:b0:32b:1b83:649a with SMTP id a6-20020a027a06000000b0032b1b83649amr9861961jac.29.1652728462508; Mon, 16 May 2022 12:14:22 -0700 (PDT) Received: from [192.168.1.172] ([207.135.234.126]) by smtp.gmail.com with ESMTPSA id w24-20020a6b4a18000000b0065a47e16f41sm63007iob.19.2022.05.16.12.14.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 16 May 2022 12:14:21 -0700 (PDT) Message-ID: <143f0708-e446-9cfe-eba8-8731d52345db@kernel.dk> Date: Mon, 16 May 2022 13:14:20 -0600 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:91.0) Gecko/20100101 Thunderbird/91.8.1 Subject: Re: [REGRESSION] lxc-stop hang on 5.17.x kernels Content-Language: en-US To: Thorsten Leemhuis , Daniel Harding , Pavel Begunkov Cc: regressions@lists.linux.dev, io-uring@vger.kernel.org, linux-kernel@vger.kernel.org, Christian Brauner References: <7925e262-e0d4-6791-e43b-d37e9d693414@living180.net> <371c01dd-258c-e428-7428-ff390b664752@kernel.dk> <2436d42c-85ca-d060-6508-350c769804f1@gmail.com> <12a57dd9-4423-a13d-559b-2b1dd2fb0ef3@living180.net> <897dc597-fc0a-34ec-84b8-7e1c4901e0fc@leemhuis.info> <41c86189-0d1f-60f0-ca8e-f80b3ccf5130@gmail.com> <3fc08243-f9e0-9cec-4207-883c55ccff78@living180.net> <13028ff4-3565-f09e-818c-19e5f95fa60f@living180.net> <469e5a9b-c7e0-6365-c353-d831ff1c5071@leemhuis.info> <1ce76b24-9185-6b2e-844e-d6a0ce42bb0f@leemhuis.info> <55ddaa3c-57a5-f17e-13a7-7427c5f1bb88@kernel.dk> <735012d3-bbda-54df-11fb-8e7b561c598d@leemhuis.info> From: Jens Axboe In-Reply-To: <735012d3-bbda-54df-11fb-8e7b561c598d@leemhuis.info> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 5/16/22 1:07 PM, Thorsten Leemhuis wrote: > > > On 16.05.22 20:39, Jens Axboe wrote: >> On 5/16/22 12:34 PM, Thorsten Leemhuis wrote: >>> On 16.05.22 20:22, Jens Axboe wrote: >>>> On 5/16/22 12:17 PM, Thorsten Leemhuis wrote: >>>>>>> Pavel, I had actually just started a draft email with the same theory >>>>>>> (although you stated it much more clearly than I could have). I'm >>>>>>> working on debugging the LXC side, but I'm pretty sure the issue is >>>>>>> due to LXC using blocking reads and getting stuck exactly as you >>>>>>> describe. If I can confirm this, I'll go ahead and mark this >>>>>>> regression as invalid and file an issue with LXC. Thanks for your help >>>>>>> and patience. >>>>>> >>>>>> Yes, it does appear that was the problem. The attach POC patch against >>>>>> LXC fixes the hang. The kernel is working as intended. >>>>>> >>>>>> #regzbot invalid: userspace programming error >>>>> >>>>> Hmmm, not sure if I like this. So yes, this might be a bug in LXC, but >>>>> afaics it's a bug that was exposed by kernel change in 5.17 (correct me >>>>> if I'm wrong!). The problem thus still qualifies as a kernel regression >>>>> that normally needs to be fixed, as can be seen my some of the quotes >>>>> from Linus in this file: >>>>> https://www.kernel.org/doc/html/latest/process/handling-regressions.html >>>> >>>> Sorry, but that's really BS in this particularly case. This could always >>>> have triggered, it's the way multishot works. Will we count eg timing >>>> changes as potential regressions, because an application relied on >>>> something there? That does not make it ABI. >>>> >>>> In general I agree with Linus on this, a change in behavior breaking >>>> something should be investigated and figured out (and reverted, if need >>>> be). This is not that. >>> >>> Sorry, I have to deal with various subsystems and a lot of regressions >>> reports. I can't know the details of each of issue and there are >>> developers around that are not that familiar with all the practical >>> implications of the "no regressions". That's why I was just trying to >>> ensure that this is something safe to ignore. If you say it is, than I'm >>> totally happy and now rest my case. :-D >> >> It's just a slippery slope that quickly leads to the fact that _any_ >> kernel change is a potential regressions, > > I know, don't worry, that's why I'm trying to be careful. But I also had > cases already where someone (even a proper subsystem maintainer) said > "this is not a regression, it's a userspace bug" and it clearly was a > kernel regression (and Linus wasn't happy when he found out). That why I I get where you're coming from, and that is indeed what most maintainers would say :-) -- Jens Axboe