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 8D4E0C433FE for ; Wed, 2 Mar 2022 02:29:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237792AbiCBCaD (ORCPT ); Tue, 1 Mar 2022 21:30:03 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44422 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235765AbiCBC34 (ORCPT ); Tue, 1 Mar 2022 21:29:56 -0500 Received: from alexa-out-sd-02.qualcomm.com (alexa-out-sd-02.qualcomm.com [199.106.114.39]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 588F7433A8; Tue, 1 Mar 2022 18:29:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; i=@quicinc.com; q=dns/txt; s=qcdkim; t=1646188153; x=1677724153; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=MW0zFik7KBrY0+AWSzro97Kd8wxqomrOCyu7g15hN74=; b=pxkTcvckHoadIfcvcQwS8AvobKxciUPG7fNl69IY2TAHkCHUh+DCbbyO 7DY3ia52S9Npbq4eq3F5xCr0WcBGVQQGl9Qc8xOZox9AMnFMBpdaAAcoe gJnKWYhBded37lqQO0Z72/Z4l1bkZvbIlNz7tdh3BPBN3vgT/5DM54IA3 g=; Received: from unknown (HELO ironmsg05-sd.qualcomm.com) ([10.53.140.145]) by alexa-out-sd-02.qualcomm.com with ESMTP; 01 Mar 2022 18:29:12 -0800 X-QCInternal: smtphost Received: from nasanex01c.na.qualcomm.com ([10.47.97.222]) by ironmsg05-sd.qualcomm.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Mar 2022 18:29:12 -0800 Received: from nalasex01a.na.qualcomm.com (10.47.209.196) by nasanex01c.na.qualcomm.com (10.47.97.222) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.15; Tue, 1 Mar 2022 18:29:12 -0800 Received: from [10.239.133.9] (10.80.80.8) by nalasex01a.na.qualcomm.com (10.47.209.196) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.15; Tue, 1 Mar 2022 18:29:08 -0800 Message-ID: Date: Wed, 2 Mar 2022 10:29:06 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.5.1 Subject: Re: [PATCH] coresight: Defer probe when the child dev is not probed Content-Language: en-US To: Suzuki K Poulose , Mike Leach CC: Mathieu Poirier , Leo Yan , Alexander Shishkin , Mao Jinlong , , , , , "Tingwei Zhang" , Yuanfang Zhang , Tao Zhang , Hao Zhang References: <20220228133112.3987-1-quic_jinlmao@quicinc.com> <861dd6e1-30dc-626e-3449-72d3b6822e7b@arm.com> <2fd9c96a-fc86-7247-d13a-a5283bb82494@arm.com> From: Jinlong Mao In-Reply-To: <2fd9c96a-fc86-7247-d13a-a5283bb82494@arm.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.80.80.8] X-ClientProxiedBy: nasanex01a.na.qualcomm.com (10.52.223.231) To nalasex01a.na.qualcomm.com (10.47.209.196) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/1/2022 11:03 PM, Suzuki K Poulose wrote: > Hi > > On 01/03/2022 13:30, Jinlong Mao wrote: >> Hi Mike, >> >> On 3/1/2022 9:15 PM, Mike Leach wrote: >>> Hi, >>> >>> On Tue, 1 Mar 2022 at 11:42, Jinlong Mao >>> wrote: >>>> On 2/28/2022 10:51 PM, Suzuki K Poulose wrote: >>>> > > ... > >>>> >>>> Hi Suzuki, >>>> >>>> This issue happens when race condition happens. >>>> The condition is that the device and its child_device's probe >>>> happens at the same time. >>>> >>>> For example: device0 and its child device device1. >>>> Both of them are calling coresight_register function. device0 is >>>> calling coresight_fixup_device_conns. >>>> device1 is waiting for device0 to release the coresight_mutex. >>>> Because device1's csdev node is allocated, >>>> coresight_make_links will be called for device0. Then in >>>> coresight_add_sysfs_link, has_conns_grp is true >>>> for device0, but has_conns_grp is false for device1 as >>>> has_conns_grp is set to true in coresight_create_conns_sysfs_group . >>>> The probe of device0 will fail for at this condition. >>>> >>>> >>>> struct coresight_device *coresight_register(struct coresight_desc >>>> *desc) >>>> { >>>>     ......... >>>>      mutex_lock(&coresight_mutex); >>>> >>>>      ret = coresight_create_conns_sysfs_group(csdev); >>>>      if (!ret) >>>>          ret = coresight_fixup_device_conns(csdev); >>>>      if (!ret) >>>>          ret = coresight_fixup_orphan_conns(csdev); >>>>      if (!ret && cti_assoc_ops && cti_assoc_ops->add) >>>>          cti_assoc_ops->add(csdev); >>>> >>>>      mutex_unlock(&coresight_mutex); >>>> >>>> ......... >>>> >>>> } >>>> >>>> static int coresight_fixup_device_conns(struct coresight_device >>>> *csdev) >>>> { >>>>     .......... >>>>          conn->child_dev = >>>> coresight_find_csdev_by_fwnode(conn->child_fwnode); >>> The issue appears to be a constraint hidden in the lower layers of >>> the code. >>> Would a better solution not be to alter the code here: >>> >>> if (conn->child_dev && conn->child_dev->has_conns_grp) { >>>     ... >>> } else { >>>        csdev->orphan = true; >>> } >>> >>> which would mean that the connection attempt would drop through to >>> label the connection as an orphan, to be cleaned up by the child >>> itself when it runs coresight_fixup_orphan_conns() >>> > > Tnanks Mike, I think that is a good solution. Alternatively, we > could make sure that device_register() and the fixup following > that are atomic. > > i.e. > >     mutex_lock() > >     device_register() >     fixup_connections() >     create_sysfs() > >     mutex_unlock(); > > The fix may be a bit invasive than Mike's proposal, but it makes > sure we don't end up with half baked device on the coresight-bus. > > Suzuki Thanks Mike & Suzuki. I will combine your proposals and make the changes. I will get back to you after the test. Thanks Jinlong Mao