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 3B5D5C433EF for ; Wed, 4 May 2022 06:55:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241638AbiEDG7Z (ORCPT ); Wed, 4 May 2022 02:59:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54924 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345211AbiEDG62 (ORCPT ); Wed, 4 May 2022 02:58:28 -0400 Received: from out1-smtp.messagingengine.com (out1-smtp.messagingengine.com [66.111.4.25]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A636D21E3B; Tue, 3 May 2022 23:54:17 -0700 (PDT) Received: from compute5.internal (compute5.nyi.internal [10.202.2.45]) by mailout.nyi.internal (Postfix) with ESMTP id 3872A5C006E; Wed, 4 May 2022 02:54:15 -0400 (EDT) Received: from mailfrontend1 ([10.202.2.162]) by compute5.internal (MEProxy); Wed, 04 May 2022 02:54:15 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=living180.net; h=cc:cc:content-transfer-encoding:content-type:date:date:from :from:in-reply-to:in-reply-to:message-id:mime-version:references :reply-to:sender:subject:subject:to:to; s=fm2; t=1651647255; x= 1651733655; bh=JEqrpWsOY9RdcvSTc4MYhkThrGU1N4YgK93BL3bHbPE=; b=c F3yMJkgUEYFeUdLTCk2bGdHLlYlCFHTImxZqwXzz/CR7BSDiUn4GqfRDHWYF7ltc 0J/U5vbn5PD/98NcyUS40xyVNHKBKTIfG3VD/H4k7oYK/hErljYKXM/sYvIKgQn8 i6tgpwSXj3gapirV7N6P/0KeBVWOEGrcvTYgF38zxFI4bH43noo/NwOqsP/E7ao+ nGpmjt0diqA7xSUdMUdp/WDhzFeoDvMqBBofHBAzUmUAs/aRlwNTDTTTA0ohF5fq IWjDwjQuFb27pQlnjstMYwqDYqhcBcvBQiTHuzVDqyR8ovvHFarK3poyc9KF+qJy lLy4uRKQ7+pylKiKuevMg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:cc:content-transfer-encoding :content-type:date:date:from:from:in-reply-to:in-reply-to :message-id:mime-version:references:reply-to:sender:subject :subject:to:to:x-me-proxy:x-me-proxy:x-me-sender:x-me-sender :x-sasl-enc; s=fm1; t=1651647255; x=1651733655; bh=JEqrpWsOY9Rdc vSTc4MYhkThrGU1N4YgK93BL3bHbPE=; b=I5pMtQos66KTI2Y+4x47HT0oI5vZQ tV9BjfCHSaXc8Oe4yNuGl7oRZvH1h6+oIdr2gPJAOu+/emYL1tI26osOuLOEq1n9 3t4gqBOCGCYFrOegynwmB1ZXkQ7n4sAh+T8L9DA7Gc6BLP3BBFo+DQ3C72J/QqYl g/EpC3bUmZwQUbM0XBqtXSCDd9cHNxXa3KHgm0f6da2Bz69iQcHsb70Qdzk3NcPA P7gOT0235z2recYFQPz/Maiu4z7q4W+v0M02zsPD9Ay7sLYGWsspXUkBVXVzaYys 3GVpr2bMi+9PDJxtRlKRnZZ4nY/sepKqBNtEthcdi1Upl0HxyQ9tXERxA== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvfedrvdekgdduudefucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhepkfffgggfuffvvehfhfgjtgfgsehtkeertddtfeejnecuhfhrohhmpeffrghn ihgvlhcujfgrrhguihhnghcuoeguhhgrrhguihhngheslhhivhhinhhgudektddrnhgvth eqnecuggftrfgrthhtvghrnhepfeffjeejffegffeuveekkeffiefghefhtefgvdehveei geeuffegfeeileeihfevnecuffhomhgrihhnpehgihhthhhusgdrtghomhenucevlhhush htvghrufhiiigvpedtnecurfgrrhgrmhepmhgrihhlfhhrohhmpeguhhgrrhguihhnghes lhhivhhinhhgudektddrnhgvth X-ME-Proxy: Received: by mail.messagingengine.com (Postfix) with ESMTPA; Wed, 4 May 2022 02:54:13 -0400 (EDT) Message-ID: <12a57dd9-4423-a13d-559b-2b1dd2fb0ef3@living180.net> Date: Wed, 4 May 2022 09:54:10 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; 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: Pavel Begunkov , Jens Axboe Cc: regressions@lists.linux.dev, io-uring@vger.kernel.org, linux-kernel@vger.kernel.org References: <7925e262-e0d4-6791-e43b-d37e9d693414@living180.net> <6ad38ecc-b2a9-f0e9-f7c7-f312a2763f97@kernel.dk> <371c01dd-258c-e428-7428-ff390b664752@kernel.dk> <2436d42c-85ca-d060-6508-350c769804f1@gmail.com> From: Daniel Harding In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/3/22 17:14, Pavel Begunkov wrote: > On 5/3/22 08:37, Daniel Harding wrote: >> [Resend with a smaller trace] >> >> On 5/3/22 02:14, Pavel Begunkov wrote: >>> On 5/2/22 19:49, Daniel Harding wrote: >>>> On 5/2/22 20:40, Pavel Begunkov wrote: >>>>> On 5/2/22 18:00, Jens Axboe wrote: >>>>>> On 5/2/22 7:59 AM, Jens Axboe wrote: >>>>>>> On 5/2/22 7:36 AM, Daniel Harding wrote: >>>>>>>> On 5/2/22 16:26, Jens Axboe wrote: >>>>>>>>> On 5/2/22 7:17 AM, Daniel Harding wrote: >>>>>>>>>> I use lxc-4.0.12 on Gentoo, built with io-uring support >>>>>>>>>> (--enable-liburing), targeting liburing-2.1.  My kernel >>>>>>>>>> config is a >>>>>>>>>> very lightly modified version of Fedora's generic kernel >>>>>>>>>> config. After >>>>>>>>>> moving from the 5.16.x series to the 5.17.x kernel series, I >>>>>>>>>> started >>>>>>>>>> noticed frequent hangs in lxc-stop.  It doesn't happen 100% >>>>>>>>>> of the >>>>>>>>>> time, but definitely more than 50% of the time. Bisecting >>>>>>>>>> narrowed >>>>>>>>>> down the issue to commit >>>>>>>>>> aa43477b040251f451db0d844073ac00a8ab66ee: >>>>>>>>>> io_uring: poll rework. Testing indicates the problem is still >>>>>>>>>> present >>>>>>>>>> in 5.18-rc5. Unfortunately I do not have the expertise with the >>>>>>>>>> codebases of either lxc or io-uring to try to debug the problem >>>>>>>>>> further on my own, but I can easily apply patches to any of the >>>>>>>>>> involved components (lxc, liburing, kernel) and rebuild for >>>>>>>>>> testing or >>>>>>>>>> validation.  I am also happy to provide any further >>>>>>>>>> information that >>>>>>>>>> would be helpful with reproducing or debugging the problem. >>>>>>>>> Do you have a recipe to reproduce the hang? That would make it >>>>>>>>> significantly easier to figure out. >>>>>>>> >>>>>>>> I can reproduce it with just the following: >>>>>>>> >>>>>>>>      sudo lxc-create --n lxc-test --template download --bdev >>>>>>>> dir --dir /var/lib/lxc/lxc-test/rootfs -- -d ubuntu -r bionic >>>>>>>> -a amd64 >>>>>>>>      sudo lxc-start -n lxc-test >>>>>>>>      sudo lxc-stop -n lxc-test >>>>>>>> >>>>>>>> The lxc-stop command never exits and the container continues >>>>>>>> running. >>>>>>>> If that isn't sufficient to reproduce, please let me know. >>>>>>> >>>>>>> Thanks, that's useful! I'm at a conference this week and hence have >>>>>>> limited amount of time to debug, hopefully Pavel has time to >>>>>>> take a look >>>>>>> at this. >>>>>> >>>>>> Didn't manage to reproduce. Can you try, on both the good and bad >>>>>> kernel, to do: >>>>> >>>>> Same here, it doesn't reproduce for me >>>> OK, sorry it wasn't something simple. >>>>> # echo 1 > /sys/kernel/debug/tracing/events/io_uring/enable >>>>>> >>>>>> run lxc-stop >>>>>> >>>>>> # cp /sys/kernel/debug/tracing/trace ~/iou-trace >>>>>> >>>>>> so we can see what's going on? Looking at the source, lxc is just >>>>>> using >>>>>> plain POLL_ADD, so I'm guessing it's not getting a notification >>>>>> when it >>>>>> expects to, or it's POLL_REMOVE not doing its job. If we have a >>>>>> trace >>>>>> from both a working and broken kernel, that might shed some light >>>>>> on it. >>>> It's late in my timezone, but I'll try to work on getting those >>>> traces tomorrow. >>> >>> I think I got it, I've attached a trace. >>> >>> What's interesting is that it issues a multi shot poll but I don't >>> see any kind of cancellation, neither cancel requests nor task/ring >>> exit. Perhaps have to go look at lxc to see how it's supposed >>> to work >> >> Yes, that looks exactly like my bad trace.  I've attached good trace >> (captured with linux-5.16.19) and a bad trace (captured with >> linux-5.17.5).  These are the differences I noticed with just a >> visual scan: >> >> * Both traces have three io_uring_submit_sqe calls at the very >> beginning, but in the good trace, there are further >> io_uring_submit_sqe calls throughout the trace, while in the bad >> trace, there are none. >> * The good trace uses a mask of c3 for io_uring_task_add much more >> often than the bad trace:  the bad trace uses a mask of c3 only for >> the very last call to io_uring_task_add, but a mask of 41 for the >> other calls. >> * In the good trace, many of the io_uring_complete calls have a >> result of 195, while in the bad trace, they all have a result of 1. >> >> I don't know whether any of those things are significant or not, but >> that's what jumped out at me. >> >> I have also attached a copy of the script I used to generate the >> traces.  If there is anything further I can to do help debug, please >> let me know. > > Good observations! thanks for traces. > > It sounds like multi-shot poll requests were getting downgraded > to one-shot, which is a valid behaviour and was so because we > didn't fully support some cases. If that's the reason, than > the userspace/lxc is misusing the ABI. At least, that's the > working hypothesis for now, need to check lxc. So, I looked at the lxc source code, and it appears to at least try to handle the case of multi-shot being downgraded to one-shot.  I don't know enough to know if the code is actually correct however: https://github.com/lxc/lxc/blob/7e37cc96bb94175a8e351025d26cc35dc2d10543/src/lxc/mainloop.c#L165-L189 https://github.com/lxc/lxc/blob/7e37cc96bb94175a8e351025d26cc35dc2d10543/src/lxc/mainloop.c#L254 https://github.com/lxc/lxc/blob/7e37cc96bb94175a8e351025d26cc35dc2d10543/src/lxc/mainloop.c#L288-L290 -- Regards, Daniel Harding