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=-8.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=no 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 33561C32771 for ; Thu, 9 Jan 2020 10:59:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0517620656 for ; Thu, 9 Jan 2020 10:59:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="WxtF6rMh" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730503AbgAIK7w (ORCPT ); Thu, 9 Jan 2020 05:59:52 -0500 Received: from mail-io1-f65.google.com ([209.85.166.65]:38230 "EHLO mail-io1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728635AbgAIK7v (ORCPT ); Thu, 9 Jan 2020 05:59:51 -0500 Received: by mail-io1-f65.google.com with SMTP id v3so6644377ioj.5 for ; Thu, 09 Jan 2020 02:59:51 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=QPi6QnVXghXv8TY7JMc2BuYgut9DZveS4sz8HSAzzAE=; b=WxtF6rMhat0yOMYOkIGw1PZioR964EQ0WGOdDWYoA4+TwrtGwcvF471ZdqnxorH+R6 JEi1bKDztJVqWgCIWLQ5bH80cEw5JZJak2XTFCVGavFicQZFC0I57NcUbrKpmb6LMCQn Ho8KowQTK6vAx+J2SE9zTNXGo9yBrJlC0mrEXy3/BVPRJ4DQf73YsijLrIt2W1mKC36m 1PsZ1RQk+yUVF1o3TrbcEtAyMCbPu5DHnO0G5bj4WPRbOMOcwwFVcIqYPfeUGYJuwM6E 0RkxNn+bxdnC4UEb7Xa8B18mFIv4FyhYRvMzcTnft+1mPcfXVyjRGHYpwzd36Gc/cpzW FTJA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=QPi6QnVXghXv8TY7JMc2BuYgut9DZveS4sz8HSAzzAE=; b=Q7ccUlDmk7z60qcHZspGGtRULSqHmIsgkb7XggBPo5PdewOAacH384hMxOgGXnNl+U bzGKtiEpVybYDUni9NqmRJidyBSQS50ye53NR6PyZupYoNYDLHaISxYgpb8h/pbvWUNR 5BIifzix4jbMjPpDCLQ7DtZNs6Im4O1GMjVQCrQhbz8bDBnVJjdiItx80avg8qFLvuNi j7LwP41cF9i/rLwdVZHjEC7k6K5ViiuNjFrBLd93gnZ0XBErDEPREFVFW56n2MAAVYaD 08SO0ock8M+psMzI+j7lAimsbmfDNv0lx/hVuBO3NRPakBBebQH+0lSmjm4FN/Xt6jD6 j2gw== X-Gm-Message-State: APjAAAUPDnWdgdRmr5tmQyhV78jbXlleCPGZyRpAbRts+SDTeW4dprOs Dw1z/FeIXk5DOAQdC5m7WeqClagpW67DQFsHqHUPQA== X-Google-Smtp-Source: APXvYqy5YRToV4ho+1HZN01NgOpFCbr14jsvMrxynyarJaFUyY1ek05rytw4zulCXWiF5tX1rdl3nX75mbjlAFbZqhc= X-Received: by 2002:a6b:8f41:: with SMTP id r62mr7053509iod.140.1578567590321; Thu, 09 Jan 2020 02:59:50 -0800 (PST) MIME-Version: 1.0 References: <20200108115007.31095-1-m.szyprowski@samsung.com> <20200108115007.31095-2-m.szyprowski@samsung.com> In-Reply-To: From: Tzung-Bi Shih Date: Thu, 9 Jan 2020 18:59:39 +0800 Message-ID: Subject: Re: [PATCH 2/2] ASoC: max98090: fix lockdep warning To: Marek Szyprowski Cc: ALSA development , Linux Kernel Mailing List , Linux Samsung SOC , Mark Brown , Sylwester Nawrocki , Dylan Reid , Jimmy Cheng-Yi Chiang , Krzysztof Kozlowski , Bartlomiej Zolnierkiewicz Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 9, 2020 at 1:36 PM Tzung-Bi Shih wrote: > On Wed, Jan 8, 2020 at 7:50 PM Marek Szyprowski > wrote: > > This fixes the following lockdep warning observed on Exynos4412-based > > Odroid U3 board: > > ====================================================== > > -> #1 (&card->controls_rwsem){++++}: > > snd_ctl_add_replace+0x3c/0x84 > > dapm_create_or_share_kcontrol+0x24c/0x2e0 > > snd_soc_dapm_new_widgets+0x308/0x594 > > snd_soc_bind_card+0x80c/0xad4 > > devm_snd_soc_register_card+0x34/0x6c > > odroid_audio_probe+0x288/0x34c > > platform_drv_probe+0x6c/0xa4 I noticed the stack is a little different than the last time (odroid_audio_probe vs. asoc_simple_probe). Did you use the same machine to test? > asoc_simple_probe+0x244/0x4a0 > platform_drv_probe+0x6c/0xa4 (https://mailman.alsa-project.org/pipermail/alsa-devel/2019-December/160142.html) > I would like to spend some time to find the root cause. It would be a > little challenging though (I have no real runtime to test...). After a few hours of study, I failed to find the reason to cause the possible circular locking. And would need more of your input. Followed the information provided in the message (https://mailman.alsa-project.org/pipermail/alsa-devel/2019-December/160535.html). As the message said "snd_soc_of_get_dai_link_codecs() return -EPROBE_DEFER". The snd_soc_of_get_dai_link_codecs( ) is before devm_snd_soc_register_card( ), and I didn't find any side effects in odroid_audio_probe( ). Only a very minor issue: snd_soc_of_put_dai_link_codecs(codec_link) will be called twice. One in snd_soc_of_get_dai_link_codecs( ) when return -EPROBE_DEFER; another one is under the label "err_put_cpu_dai". (https://elixir.bootlin.com/linux/v5.5-rc5/source/sound/soc/samsung/odroid.c#L328) The code doesn't generate any side effects because of snd_soc_of_put_dai_link_codecs( )'s robustness. Another minor thing: odroid_card_dais is not immutable but odroid_audio_probe( ) would try to modify it (https://elixir.bootlin.com/linux/v5.5-rc5/source/sound/soc/samsung/odroid.c#L295). Again, I don't think it would produce any troubles. I guess no machine would have multiple sound cards, share the same machine driver, and unbind/bind in runtime. > It is weird: userspace should not see things (e.g. no controlC0) until > snd_card_register( ). (based on today's broonie/sound.git/for-next) I would like to provide you more information about this statement to help you find further information. When userspace can see the control device? Ideally, snd_soc_bind_card( ) -> snd_card_register( ) -> snd_device_register_all( ) -> __snd_device_register( ) -> snd_ctl_dev_register( ) -> snd_register_device( ). If you look at the calling stack of possible circular locking, snd_soc_dapm_new_widgets( ) is before snd_card_register( ). That's why we think userspace should not see control devices (i.e. controlC0, controlC1, ...) and should not be able to set mixer control via ioctl( ). As this may not directly be related to the issue, could you share the init script of alsactl in your system? Does it follow the convention? (i.e. sound card is ready when receives controlC* changed event in udev rule 78-sound-card.rules) > 6. when userspace init scripts (alsactl) enumerates devices (https://mailman.alsa-project.org/pipermail/alsa-devel/2019-December/160535.html)