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mx.microsoft.com 1; spf=pass smtp.mailfrom=intel.com; dmarc=pass action=none header.from=intel.com; dkim=pass header.d=intel.com; arc=none Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=intel.com; Received: from MW4PR11MB6909.namprd11.prod.outlook.com (2603:10b6:303:224::12) by SN7PR11MB7567.namprd11.prod.outlook.com (2603:10b6:806:328::10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9434.6; Wed, 17 Dec 2025 07:05:05 +0000 Received: from MW4PR11MB6909.namprd11.prod.outlook.com ([fe80::28da:9438:a3ef:19c0]) by MW4PR11MB6909.namprd11.prod.outlook.com ([fe80::28da:9438:a3ef:19c0%7]) with mapi id 15.20.9412.005; Wed, 17 Dec 2025 07:05:05 +0000 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="UTF-8" Date: Wed, 17 Dec 2025 08:05:10 +0100 Message-ID: To: Tvrtko Ursulin , Sebastian Brzezinka , CC: Subject: Re: [PATCH i-g-t] tools/intel_gpu_top: prevent losing original pointer on realloc failure From: Sebastian Brzezinka X-Mailer: aerc 0.21.0 References: <257cafe7-a9ff-47d1-a862-488305b169a5@ursulin.net> In-Reply-To: <257cafe7-a9ff-47d1-a862-488305b169a5@ursulin.net> X-ClientProxiedBy: WA2P291CA0013.POLP291.PROD.OUTLOOK.COM (2603:10a6:1d0:1e::14) To MW4PR11MB6909.namprd11.prod.outlook.com (2603:10b6:303:224::12) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MW4PR11MB6909:EE_|SN7PR11MB7567:EE_ X-MS-Office365-Filtering-Correlation-Id: 79577bf7-9290-40f6-7c51-08de3d3a9b5a X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|366016; 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If realloc failed, it would return NULL and overwrite the >> original pointer, causing a memory leak and leaving engines inaccessible= . >> This patch uses a temporary pointer for realloc and only updates engines >> after a successful allocation, ensuring the original pointer is preserve= d >> on failure and preventing data loss. > > I don't see a memory leak, or any other problem really. If realloc fails= =20 > the flow is this: > > static struct engines *discover_engines(char *device) > { > ... > engines =3D realloc(engines, sizeof(struct engines) + > engines->num_engines * sizeof(struct engine)); > if (!engines) { > ret =3D errno; > break; > } > ... > if (ret) { > errno =3D ret; > goto err; > } > ... > return NULL; > > > > > engines =3D discover_engines(pmu_device); > if (!engines) { > fprintf(stderr, > "Failed to detect engines! (%s)\n(Kernel 4.16 or newer is required=20 > for i915 PMU support.)\n", > strerror(errno)); > ret =3D EXIT_FAILURE; > goto err_engines; > } > > So tools exits with an error message. Maybe I am blind but, again, I=20 > don't see a problem? When realloc fails, it returns NULL. If we assign that NULL value directly = to the original pointer, we lose the only reference to the previously allocated me= mory. Since that memory is no longer accessible and cannot be freed, it effective= ly becomes a memory leak for the remainder of the program=E2=80=99s execution.= The operating system will reclaim the memory when the program exits, but during the progr= am=E2=80=99s lifetime, the leak still exists. After the failure, execution jumps to err_= engines, which skips the cleanup normally performed by free_engines(engines) --=20 Best regards, Sebastian