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Thu, 9 Dec 2021 20:06:59 +0000 Date: Thu, 9 Dec 2021 12:06:57 -0800 From: Nicolin Chen To: Dmitry Osipenko CC: , , , , , , , Subject: Re: [PATCH v8 6/6] iommu/tegra-smmu: Add pagetable mappings to debugfs Message-ID: <20211209200657.GB35858@Asurada-Nvidia> References: <20211209073822.26728-1-nicolinc@nvidia.com> <20211209073822.26728-7-nicolinc@nvidia.com> <5713902d-823b-63ca-00c9-aa6c64c1af41@gmail.com> <20211209193253.GB34762@Asurada-Nvidia> <97a32c9a-2ec7-6579-7d8d-026d6f820a3e@gmail.com> <20211209195128.GA35526@Asurada-Nvidia> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 726f8ad7-3b3b-4128-0f3e-08d9bb4f85fc X-MS-TrafficTypeDiagnostic: BN8PR12MB3009:EE_ X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:10000; X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Dec 2021 20:07:26.9803 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 726f8ad7-3b3b-4128-0f3e-08d9bb4f85fc X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[203.18.50.13];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: DM6NAM11FT035.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN8PR12MB3009 Precedence: bulk List-ID: X-Mailing-List: linux-tegra@vger.kernel.org On Thu, Dec 09, 2021 at 10:58:15PM +0300, Dmitry Osipenko wrote: > External email: Use caution opening links or attachments > > > 09.12.2021 22:51, Nicolin Chen пишет: > > On Thu, Dec 09, 2021 at 10:40:42PM +0300, Dmitry Osipenko wrote: > >> External email: Use caution opening links or attachments > >> > >> > >> 09.12.2021 22:32, Nicolin Chen пишет: > >>> On Thu, Dec 09, 2021 at 05:47:18PM +0300, Dmitry Osipenko wrote: > >>>> External email: Use caution opening links or attachments > >>>> > >>>> > >>>> 09.12.2021 10:38, Nicolin Chen пишет: > >>>>> @@ -545,6 +719,15 @@ static void tegra_smmu_detach_as(struct tegra_smmu *smmu, > >>>>> if (group->swgrp != swgrp) > >>>>> continue; > >>>>> group->as = NULL; > >>>>> + > >>>>> + if (smmu->debugfs_mappings) { > >>>> Do we really need this check? > >>>> > >>>> Looks like all debugfs_create_dir() usages in this driver are incorrect, > >>>> that function never returns NULL. Please fix this. > >>> debugfs_create_dir returns ERR_PTR on failure. So here should be > >>> to check !IS_ERR. Thanks for pointing it out! > >>> > >> > >> All debugfs functions handle IS_ERR(). GregKH removes all such checks > >> all over the kernel. So the check shouldn't be needed at all, please > >> remove it if it's unneeded or prove that it's needed. > > > > debugfs_create_file can handle a NULL parent, but not ERR_PTR one, > > and then it puts the new node under the root. So either passing an > > ERR_PTR parent or creating orphan nodes here doesn't sound good... > > > > What makes you say so? Please show the exact source code that will cause > the problem. > > The smmu->debugfs_mappings can't ever be NULL and debugfs_create_file > handles the ERR_PTR [1][2]. Ah...my tool jumps to start_creating in fs/tracefs/inode.c instead. Thanks for the reply. I will remove the if line then.