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Wed, 8 Jan 2025 22:50:40 +0000 Date: Wed, 8 Jan 2025 14:50:36 -0800 From: Dan Williams To: Alistair Popple , , , CC: Alistair Popple , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v5 03/25] fs/dax: Don't skip locked entries when scanning entries Message-ID: <677f013c1466_f58f29466@dwillia2-xfh.jf.intel.com.notmuch> References: <6d25aaaadc853ffb759d538392ff48ed108e3d50.1736221254.git-series.apopple@nvidia.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <6d25aaaadc853ffb759d538392ff48ed108e3d50.1736221254.git-series.apopple@nvidia.com> X-ClientProxiedBy: MW4PR03CA0234.namprd03.prod.outlook.com (2603:10b6:303:b9::29) To PH8PR11MB8107.namprd11.prod.outlook.com (2603:10b6:510:256::6) X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH8PR11MB8107:EE_|SA3PR11MB8120:EE_ X-MS-Office365-Filtering-Correlation-Id: 9db6147f-544e-4cbe-0894-08dd3036dff3 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|7416014|1800799024; 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> > This is problematic because get_unlocked_entry() will get the next > present entry in the range, and the next entry may not be > locked. Therefore any processing of the original locked entry will be > skipped. This can cause dax_layout_busy_page_range() to miss DMA-busy > pages in the range, leading file systems to free blocks whilst DMA > operations are ongoing which can lead to file system corruption. > > Instead callers from within a xas_for_each() loop should be waiting > for the current entry to be unlocked without advancing the XArray > state so a new function is introduced to wait. Oh wow, good eye! Did this trip up an xfstest, or did you see this purely by inspection? > Also while we are here rename get_unlocked_entry() to > get_next_unlocked_entry() to make it clear that it may advance the > iterator state. Outside of the above clarification of how found / end user effect you can add: Reviewed-by: Dan Williams