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Date: Wed, 10 Jan 2024 12:25:57 -0800 From: Vikram Garhwal To: Julien Grall Cc: Javi Merino , xen-devel@lists.xenproject.org, Stefano Stabellini Subject: Re: [PATCH for-4.18 v1] xen/common: Don't dereference overlay_node after checking that it is NULL Message-ID: References: <6b2db92de764b6031647926d27cb14dd455eff7d.1704809355.git.javi.merino@cloud.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: MW4PR04CA0348.namprd04.prod.outlook.com (2603:10b6:303:8a::23) To MW3PR12MB4409.namprd12.prod.outlook.com (2603:10b6:303:2d::23) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MW3PR12MB4409:EE_|SN7PR12MB7882:EE_ X-MS-Office365-Filtering-Correlation-Id: e1171a19-c26e-463d-ab71-08dc121a60f9 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:MW3PR12MB4409.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230031)(376002)(39860400002)(366004)(346002)(136003)(396003)(230922051799003)(451199024)(64100799003)(186009)(1800799012)(8676002)(8936002)(6512007)(316002)(53546011)(6506007)(54906003)(26005)(2616005)(83380400001)(6486002)(66556008)(66476007)(66946007)(41300700001)(86362001)(6916009)(6666004)(966005)(478600001)(5660300002)(36756003)(38100700002)(2906002)(4326008)(44832011);DIR:OUT;SFP:1101; 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On Tue, Jan 09, 2024 at 03:31:55PM +0000, Julien Grall wrote: > Hi Javi, > > Title: Any reason this is titled for-4.18? Shouldn't this patch also be > merged in staging? > > On 09/01/2024 14:19, Javi Merino wrote: > > In remove_nodes(), overlay_node is dereferenced when printing the > > error message even though it is known to be NULLL. Fix the error > > Typo: s/NULLL/NULL/ > > This can be fixed on commit if there is nothing else. > > > message to avoid dereferencing a NULL pointer. > > > > The semantic patch that spots this code is available in > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/scripts/coccinelle/null/deref_null.cocci?id=1f874787ed9a2d78ed59cb21d0d90ac0178eceb0 > > Good catch and glad to see that coccinelle can work on Xen. I am looking > forward for more work in that area :). > > > > > Fixes: 7e5c4a8b86f1 ("xen/arm: Implement device tree node removal functionalities") > > Signed-off-by: Javi Merino > c> --- > > CC: Vikram Garhwal > > > > Vikram, I didn't know what to put in the error message. Feel free to > > suggest something more appropriate than "Device not present in the > > tree". > > More questions for Vikram, looking at the code, it is not 100% clear in > which condition overlay_node could be NULL. Is this a programming error? if > so, maybe this should be an ASSERT_UNREACHABLE() (could be added separately) > and it would be fine to print nothing. > This can happen with failures in add_nodes() function. add_nodes() failure will try to call remove_nodes function. Depending on where add_nodes() is failed, nodes_address may or may not be NULL. We also added a detailed comment on this: https://github.com/xen-project/xen/blob/5a3ace21f3d779b291a2d305824b2820d88de7f1/xen/common/dt-overlay.c#L816 For now, we can return from here without printing anything as error message will be printed by the caller of remove_nodes() anyway. > Cheers, > > -- > Julien Grall