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Mon, 25 May 2020 06:28:48 +0000 Received: from BN6PR11MB3954.namprd11.prod.outlook.com ([fe80::c05b:5a81:29d8:6b7f]) by BN6PR11MB3954.namprd11.prod.outlook.com ([fe80::c05b:5a81:29d8:6b7f%6]) with mapi id 15.20.3021.029; Mon, 25 May 2020 06:28:48 +0000 Subject: Re: [PATCH] workqueue: Fix double kfree(rescuer) in destroy_workqueue() To: Markus Elfring , Lai Jiangshan , Tejun Heo Cc: linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org References: <96b49f22-50a7-9c8f-7c9d-f178195de717@web.de> From: qzhang2 Message-ID: Date: Mon, 25 May 2020 14:28:28 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 In-Reply-To: <96b49f22-50a7-9c8f-7c9d-f178195de717@web.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-ClientProxiedBy: HK2PR02CA0133.apcprd02.prod.outlook.com (2603:1096:202:16::17) To BN6PR11MB3954.namprd11.prod.outlook.com (2603:10b6:405:79::35) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [128.224.162.183] (60.247.85.82) by HK2PR02CA0133.apcprd02.prod.outlook.com (2603:1096:202:16::17) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3021.24 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: AApfSbzYdwQV5g87E6RkS6eSaVlTNUW61OhX507VI3DR8ERJos5VgmdzGWBHrctZbs3lNmVygKToFCZUagJVINp33woZJgSs0G3baFiNNBJrQjOO6PSZeIb36xSRCt1pEyVcCXBVnhk369DUbWMJKNqBkAmicUM7dKZfy056ErTZYA4HIA2Ks0iwRxAaM8wYuBcmpIg4gqoHFMiug+GyX0ixfSR1S8UnSmTfJWm/Lkae3JToah1IU9xzPKJtmOU1QDxMSa8oiCvzW0mZ4jrm9YZgj5pXIHdVvXK7H/jR9w2veHFVVio358Wp4YduQ+I5D55T3eA62VOuk3d7Q+EB6Bw85xiGQ5BK+PSvJH3Rs6jYVyY//ihum7MyDmdzzHLVRKb4ftodzEKqRpBRNjA7vrQ1Kb9F3tFLlmE9YbovMtFdvHYqVYWPAMMU0m4WZuuiXM32wZUS87YAyvunQRdCQ/AWHQfeJewuX3M1MqCXwmM= X-OriginatorOrg: windriver.com X-MS-Exchange-CrossTenant-Network-Message-Id: 44aad4aa-dc63-4f77-bd0f-08d80074e211 X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 May 2020 06:28:48.4353 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ddb2873-a1ad-4a18-ae4e-4644631433be X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: lAePpH2QrhvmLJpgcUPwhF3VzRhBWBW88oA8C6iGjp64Aj7eq4St91FtXHPApVQYZo+dI4IiMO2cCELV8zNVyi9/nlYOU+0LElNfEYbDW5I= X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN6PR11MB1921 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Sorry I didn't describe clearly I describe the meaning as follows: destroy_workqueue if(wq->rescuer) struct worker *rescuer = wq->rescuer kfree(rescuer) .................. if (!(wq->flags & WQ_UNBOUND)) call_rcu(&wq->rcu, rcu_free_wq) ...................... rcu_free_wq kfree(wq->rescuer) there are double free. On 5/24/20 11:33 PM, Markus Elfring wrote: >> When destroy_workqueue if rescuer worker exist,wq->rescuer pointer be >> kfree. if sanity checks passed. the func call_rcu(&wq->rcu, rcu_free_wq) >> will be called if the wq->flags & WQ_UNBOUND is false,in rcu_free_wq >> func wq->rescuer pointer was kfree again. > > 1. I suggest to improve also this change description. > Do you try to explain here that a call of the function “free_workqueue_attrs” > (or “free_percpu”) would perform sufficient clean-up of system resources > in this use case? > > 2. You proposed to delete the function call “kfree(wq->rescuer)” from > the implementation of the function “rcu_free_wq”. > https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/kernel/workqueue.c?id=c11d28ab4a691736e30b49813fb801847bd44e83#n3482 > https://elixir.bootlin.com/linux/v5.7-rc6/source/kernel/workqueue.c#L3482 > > This function name should be specified also in the patch subject, > shouldn't it? > > 3. Would you like to add the tag “Fixes” to the commit message? > > Regards, > Markus >