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 31E5EEB64DA for ; Thu, 15 Jun 2023 16:47:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236680AbjFOQra (ORCPT ); Thu, 15 Jun 2023 12:47:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42876 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236080AbjFOQrF (ORCPT ); Thu, 15 Jun 2023 12:47:05 -0400 Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C5D583599 for ; Thu, 15 Jun 2023 09:46:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1686847598; x=1718383598; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=PiVRmi1vjOZiGqiH/BFR7jdTY/8M9iyE6yzFyqVXpIo=; b=YbF4ENe+YzyHTkJV+KcKPZUaah8uQqP4q3icGDtiWBv3Jggnp9OeaOS8 sfvlpV0WJag6MmklVXHAjFRTsTJFpAuHk2erDDxLru89UrTfxa6qbs/xF PCraT0Ua+3wmgLartDWtUC6vS4WH6NfuuaAX56DHnunmHJ+dbAZik7ZXq Hf32ZFdzLIdGaAsNY5Q9Ozetfaivugj8sdshTf66AGujc4CUiy1fjOlaw ZwQI2QCdaM1hMgOWCT06vbQwScC0PgGjzlYeAIhSYR6KAaUh0dZG/TQsz NWLssKaUcjOJ9OnA+onwyqFBEnPBI3XjfsIttZflLiIA26ocG3n2Mqxfl A==; X-IronPort-AV: E=McAfee;i="6600,9927,10742"; a="387506744" X-IronPort-AV: E=Sophos;i="6.00,245,1681196400"; d="scan'208";a="387506744" Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Jun 2023 09:46:23 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10742"; a="857040434" X-IronPort-AV: E=Sophos;i="6.00,245,1681196400"; d="scan'208";a="857040434" Received: from mrejmak-mobl.ger.corp.intel.com (HELO [10.252.36.104]) ([10.252.36.104]) by fmsmga001-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Jun 2023 09:46:21 -0700 Message-ID: <2f010db3-73be-2cdd-0aef-62ec212769c1@linux.intel.com> Date: Thu, 15 Jun 2023 18:31:27 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Firefox/102.0 Thunderbird/102.11.0 Subject: Re: [PATCH 1/2] soundwire: bus: Prevent lockdep asserts when stream has multiple buses Content-Language: en-US To: Richard Fitzgerald , vkoul@kernel.org, yung-chuan.liao@linux.intel.com Cc: alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org, patches@opensource.cirrus.com References: <20230615141208.679011-1-rf@opensource.cirrus.com> From: Pierre-Louis Bossart In-Reply-To: <20230615141208.679011-1-rf@opensource.cirrus.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/15/23 16:12, Richard Fitzgerald wrote: > Give the bus_lock and msg_lock of each bus a different unique key > so that it is possible to acquire the locks of multiple buses > without lockdep asserting a possible deadlock. > > Using mutex_init() to initialize a mutex gives all those mutexes > the same lock class. Lockdep checking treats it as an error to > attempt to take a mutex while already holding a mutex of the same > class. This causes a lockdep assert when sdw_acquire_bus_lock() > attempts to lock multiple buses, and when do_bank_switch() takes > multiple msg_lock. > > [ 138.697350] WARNING: possible recursive locking detected > [ 138.697366] 6.3.0-test #1 Tainted: G E > [ 138.697380] -------------------------------------------- > [ 138.697394] play/903 is trying to acquire lock: > [ 138.697409] ffff99b8c41aa8c8 (&bus->bus_lock){+.+.}-{3:3}, at: > sdw_prepare_stream+0x52/0x2e0 > [ 138.697443] > but task is already holding lock: > [ 138.697468] ffff99b8c41af8c8 (&bus->bus_lock){+.+.}-{3:3}, at: > sdw_prepare_stream+0x52/0x2e0 > [ 138.697493] > other info that might help us debug this: > [ 138.697521] Possible unsafe locking scenario: > > [ 138.697540] CPU0 > [ 138.697550] ---- > [ 138.697559] lock(&bus->bus_lock); > [ 138.697570] lock(&bus->bus_lock); > [ 138.697581] > *** DEADLOCK *** > > Giving each mutex a unique key allows multiple to be held > without triggering a lockdep assert. But note that it does not > allow them to be taken in one order then a different order. > If two mutexes are taken in the order A, B then they must > always be taken in that order otherwise they could deadlock. > > Signed-off-by: Richard Fitzgerald Reviewed-by: Pierre-Louis Bossart > --- > drivers/soundwire/bus.c | 15 +++++++++++++-- > include/linux/soundwire/sdw.h | 3 +++ > 2 files changed, 16 insertions(+), 2 deletions(-) > > diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c > index b44f8d0affa6..dba920ec88f6 100644 > --- a/drivers/soundwire/bus.c > +++ b/drivers/soundwire/bus.c > @@ -69,8 +69,17 @@ int sdw_bus_master_add(struct sdw_bus *bus, struct device *parent, > return -EINVAL; > } > > - mutex_init(&bus->msg_lock); > - mutex_init(&bus->bus_lock); > + /* > + * Give each bus_lock and msg_lock a unique key so that lockdep won't > + * trigger a deadlock warning when the locks of several buses are > + * grabbed during configuration of a multi-bus stream. > + */ > + lockdep_register_key(&bus->msg_lock_key); > + __mutex_init(&bus->msg_lock, "msg_lock", &bus->msg_lock_key); > + > + lockdep_register_key(&bus->bus_lock_key); > + __mutex_init(&bus->bus_lock, "bus_lock", &bus->bus_lock_key); > + > INIT_LIST_HEAD(&bus->slaves); > INIT_LIST_HEAD(&bus->m_rt_list); > > @@ -181,6 +190,8 @@ void sdw_bus_master_delete(struct sdw_bus *bus) > sdw_master_device_del(bus); > > sdw_bus_debugfs_exit(bus); > + lockdep_unregister_key(&bus->bus_lock_key); > + lockdep_unregister_key(&bus->msg_lock_key); > ida_free(&sdw_bus_ida, bus->id); > } > EXPORT_SYMBOL(sdw_bus_master_delete); > diff --git a/include/linux/soundwire/sdw.h b/include/linux/soundwire/sdw.h > index c076a3f879b3..f523ceabd059 100644 > --- a/include/linux/soundwire/sdw.h > +++ b/include/linux/soundwire/sdw.h > @@ -5,6 +5,7 @@ > #define __SOUNDWIRE_H > > #include > +#include > #include > #include > > @@ -907,7 +908,9 @@ struct sdw_bus { > struct list_head slaves; > DECLARE_BITMAP(assigned, SDW_MAX_DEVICES); > struct mutex bus_lock; > + struct lock_class_key bus_lock_key; > struct mutex msg_lock; > + struct lock_class_key msg_lock_key; > int (*compute_params)(struct sdw_bus *bus); > const struct sdw_master_ops *ops; > const struct sdw_master_port_ops *port_ops;