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 D75C0C433EF for ; Sun, 29 May 2022 06:41:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229592AbiE2GlP (ORCPT ); Sun, 29 May 2022 02:41:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48424 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229531AbiE2GlG (ORCPT ); Sun, 29 May 2022 02:41:06 -0400 Received: from mail-oi1-x230.google.com (mail-oi1-x230.google.com [IPv6:2607:f8b0:4864:20::230]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1FA0113FAA for ; Sat, 28 May 2022 23:41:05 -0700 (PDT) Received: by mail-oi1-x230.google.com with SMTP id l84so10485137oif.10 for ; Sat, 28 May 2022 23:41:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=3/+ZUmZdmdw27pbnk++KxX9Rw+MSygX4g2fczs64fyE=; b=CcmLGRWyjudLTA0cBaYrBr8cVaFy2IWaKgvpr1tBrYbZcuSIgPqjmQsu7seW6hjdvg 7r+UTw2DXBhyzCpicDqHEjU7SQr28DDR+MDOKwFpZSdoGqDjMlEjs3lF/9qeh54NgpdB q064+p03AAGeo4znajn1zW1en04tCZIcK/LTGoj2r/XoDQ3BWDi12KHAcXbf4f4seR6k 3ibij6FpHUiLhEwS1U2YSk9fDGrb06q3EShIwlIQrcKFmz0/uFs+AeY0dD8rz4d7eqAt C2ybsuMHC/VdR2eFl/lC4FXI5YFHC0f4TS4QbGTJ1cDRsAB9BoklSMxDUlg857cGof5P IVKA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=3/+ZUmZdmdw27pbnk++KxX9Rw+MSygX4g2fczs64fyE=; b=q1mc4Xvr1RtNJOLdZ5yo1OV31VBJhZpO4gtc+BrMgraOaalTSYMuDTi7cZC5mH46Ir 1Ifo7E/OkQabEdVZQWctHYevjGbfgaSo3lIeShKc3sd5HqgJED5VHyUz4pk368dwiOIU IZlLUELO6Yg7a+2KcL6rf6+W3SPIkSG+M6hyZ0y4YC6FQdKR0bZS2k0zGbs1B/lVFO5Q 0hqegMcS4gSHqpDUEZEubuPuvzjo7J5wE2h87wU7D+m7/nSen6sprNk9CFm1nbF3uRNw SI0NvR90VAydODe9r7FMBYjVVQs/yHgw/Q9KmvCZKUdzbrbwwgeF7S7F6Fhy5s/i98qD LZ5Q== X-Gm-Message-State: AOAM531Ln4lYh7EX98T1X/xjEedMHoOciNFagDJHZymiB8xqnZx0HBNb bJVcMK+TTY81kpW7O8FVBE0= X-Google-Smtp-Source: ABdhPJyE7sTwpgil3vRPOYXq11seATTAm8mRf+IEJj701waMQXcurP69qSSuWiqw9J/scvnUq9Jblw== X-Received: by 2002:a05:6808:209e:b0:32b:22fe:bf7 with SMTP id s30-20020a056808209e00b0032b22fe0bf7mr6787417oiw.127.1653806464475; Sat, 28 May 2022 23:41:04 -0700 (PDT) Received: from geday ([2804:7f2:8006:5ec0:8108:8ab5:1f16:73fe]) by smtp.gmail.com with ESMTPSA id t9-20020a056830082900b006060322124csm3702547ots.28.2022.05.28.23.41.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 28 May 2022 23:41:04 -0700 (PDT) Date: Sun, 29 May 2022 03:41:00 -0300 From: Geraldo Nascimento To: Tejun Heo Cc: Lai Jiangshan , LKML Subject: Re: [PATCH] workqueue: missing NOT while checking if Workqueue is offline Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, May 28, 2022 at 08:14:23PM -1000, Tejun Heo wrote: > On Sun, May 29, 2022 at 02:53:39AM -0300, Geraldo Nascimento wrote: > > On Sat, May 28, 2022 at 07:24:41PM -1000, Tejun Heo wrote: > > > On Sun, May 29, 2022 at 01:29:32AM -0300, Geraldo Nascimento wrote: > > > > I would like very much to hear the opinion of the maintainers! > > > > > > I have a hard time understanding what you're trying to do. Can you please > > > slow down and start from describing the problem itself? > > > > Hi Tejun, > > > > Sorry for the hurry. > > > > The problem is best described in https://gitlab.freedesktop.org/drm/amd/-/issues/1898 > > > > From my understanding from the context of __cancel_work_timer() we should not > > ever call __flush_work() but I may be wrong. In the present case as > > Yeah, you're wrong. > No problem from my side, sorry for wasting your time. > > described in AMD's GitLab __cancel_work_timer() is being called by > > cancel_delayed_work_sync() inside kfd_process_notifier_release() > > from drivers/gpu/drm/amd/amdkfd/kfd_process.c:1157 (Linux 5.18). > > Have you confirmed that that actually is the warning which is triggering? I > don't see how that condition would trigger that late during the boot and the > warning line being reported doesn't match v5.16 source code, so I'm not sure > but skimming the instructon sequence, that's the second UD2 sequence, so I'm > gonna guess that's the second WARN_ON - the !work->func one and someone else > on the gitlab bug report seems to agree too. While I can confirm from my dmesg traces it's the second WARN_ON (the one on (!work->func)) that triggers, remember it's being called from __flush_work() due to the lack of NOT operator on wq_online, inside __cancel_work_timer(). To be honest, for me, it only makes sense to call __flush_work() from the context of __cancel_work_timer() if we are sure the work isn't executing. One of the few ways to be sure is when kthreads haven't initialized yet, that means workqueue_init() hasn't fired yet and wq_online is still false, so it makes sense to negate that false and exceptionally call __flush_work() without waiting for completion of the work - i.e., __flush_work() will WARN_ON workqueue offline condition and return false immediately because task was already idle. I know I may be repeating myself, but I'm trying to make my point, from the little understanding I have of the kernel. And I know that you know best, and that the possibility of a bug like that lying undiscovered on a code-base as scrutinized as the Linux kernel is, is very small. > > It's usually a lot more helpful if the bug report is complete - include the > full warning message with some context at least, make sure that the kernel > you're using is an upstream one or something close enough. If not, point to > the source tree. Also, try to clearly distinguish what you know and what you > suspect. Both can help but mixing them up together tends to cause confusion > for everyone involved. Sorry. Will try to do better. > > It just looks like the code is trying to cancel a work item which hasn't > been initialized and what it prolly needs is an ifdef around that cancel > call depending on the config option. Thanks for looking into it, Geraldo Nascimento > > Thanks. > > -- > tejun