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Fri, 5 Nov 2021 09:18:24 +0000 Date: Fri, 5 Nov 2021 12:18:14 +0300 From: Dan Carpenter To: Ming Lei Cc: Sergey Senozhatsky , linux-block@vger.kernel.org Subject: Re: [bug report] zram: avoid race between zram_remove and disksize_store Message-ID: <20211105091638.GA2026@kadam> References: <20211104114830.GA4962@kili> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-ClientProxiedBy: AM6P193CA0079.EURP193.PROD.OUTLOOK.COM (2603:10a6:209:88::20) To MWHPR1001MB2365.namprd10.prod.outlook.com (2603:10b6:301:2d::28) MIME-Version: 1.0 Received: from kadam (102.222.70.114) by AM6P193CA0079.EURP193.PROD.OUTLOOK.COM (2603:10a6:209:88::20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4669.11 via Frontend Transport; Fri, 5 Nov 2021 09:18:21 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: fa4b0314-aeec-43fa-60f8-08d9a03d37f1 X-MS-TrafficTypeDiagnostic: CO1PR10MB4705: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:7219; 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> > > > This double frees it. > > No. > > Inside zram_reset_device(), if init_done()(zram->disksize) is zero, zram_reset_device() > returns immediately, otherwise zram->disksize is cleared and zram_meta_free() > is run in zram_reset_device(). Meantime zram->init_lock protects the > reset and disksize_store(). > > The 2nd zram_reset_device() can only reset device if disksize_store() sets new > zram->disksize and allocates new meta after the 1st zram_reset_device(). > > Seems smatch static checker need to be improved to cover this case? Yep. It's a bug in Smatch. It's supposed to parse this correctly. I will investigate. Thanks! regards, dan carpenter