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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) Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: 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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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?n3WBxbNGwNyKlqzVynWwSG984+sH/99pIzDQTS/CwriYQ0v81qPZtQpM458w?= =?us-ascii?Q?5g/ohlGqsTWn7CTki+xPHNUExj5ytGjohV4VcfhP32jp/DBnDIhVZTnO3xqe?= =?us-ascii?Q?04l1ZfuTHwV/MFxGIIiDCaapjawwQsGjEX9C9SmaWTBWqw05qfILUPBEnpFV?= =?us-ascii?Q?O6AGcSLdKeEWH+fHmd24tG2FCfsg7aTocUXItuCW0WWXEHhKfKiAmM17r+x6?= =?us-ascii?Q?dj0MEBde3a5O80odU12I3MyeBSowxa5HFgEG+vLwp5jLo2J4m27w1KA/Um3a?= =?us-ascii?Q?u3QjvRY5CuLhtd4N2LRCke5Vla7w1VPZspPzjzDf8DvP87HB3xo3ZvRwfAb4?= =?us-ascii?Q?jOKaqSbIr9iuuonDbisSTyBhMcW6U75Ul3pkku+A1QK9oGRrh6eczpZDy5Sh?= =?us-ascii?Q?wAzdxPkguFD1C6SSakcmsaAJXWREsr/R9SWXVKmQ0cZ6il66Hgwv6T2P7ig8?= =?us-ascii?Q?E7ewJkdr4Hlj72cWDrD8PIep2oIffW/uK88u4n2K+6PxQLAPAzrJUCawMk/p?= =?us-ascii?Q?uehf+JQ39ASyNo6EhNPTAS4wfmZ6UMaE8EHxb4mb6hZSSEnVxqToRqcWJT1x?= =?us-ascii?Q?uhwYObckOSlW4FW5kt1RkZXIwVrv2HEMS8pQ3ycO5Z8n+JWc7Y2NMPA3lc0n?= =?us-ascii?Q?yE4eCNNke7OxRDKyr6df7enSMvzKglx/M3rhJtPugIdwWq9q0I6WW6LXsUmz?= =?us-ascii?Q?XEITH4NrjooBsddaE8L6ecRFpoGCbWvhAL0MbxGWBsK8N3PnETtT1f2GhxVV?= =?us-ascii?Q?pGg9oDE3COsR+qRZweTMMds9gEKKikn4QIdHdqxO9A8CP1UEKUvzY70gRy6W?= =?us-ascii?Q?P0u7VY/b2SqD/95XXi8WNX3l1U3EV8O3ULNrCXK9DNxgwQbDNwxYt19pGuSj?= =?us-ascii?Q?kXus/0TPaUIp2OejOUC1lVWjFhhHO74TWHiHFYotjGFsbBuAvwJrlaSR/8+u?= =?us-ascii?Q?pFs8muZkSCd6MInA4qY6TUkkNwaVgvBRR/dHmo7Xcg5jo1+LyJSegIJW02Yt?= =?us-ascii?Q?A1Nsqs1kMH9OdLn1HKlMbUlUy6HMa9w7z0lL9O4fcAql4iyz58dFuagw9EVd?= =?us-ascii?Q?eVK3lJLYvQ06PC4nxRlI/dZSGzyeIO0EBZ3Sf7EIMlduP9+av5++S07eHVif?= =?us-ascii?Q?J2XMnAK8v3JGR8RQncbB2ARop+3wc+CG5VpN2uQ1w0E9nqIS/EQdE19cyaG8?= =?us-ascii?Q?+lwOjzN1vsmxzqhKry16b98wsL8sXjYeojrFl2S6ymDdSEhX0PSBMq0hZ2ek?= =?us-ascii?Q?r+UZc2IXLDKk+tiTzHuicJRTvxhvaZqPjzllmXBr2DcP5fwpkzDD7brJkwRl?= =?us-ascii?Q?Zeew2YA0qzqxtbrB9N8g2v7el7COYjB9kZgEhzQnXU/uX+0ihXEjPHdvJ0+N?= =?us-ascii?Q?/0DlEwcDGxfQ4blLlRV5oqVCYgudbtgrKGP6a2a+rL7lsmEZ58lKxxC3DYLH?= =?us-ascii?Q?RviEd9TAXKm8vDQklNMmVkA7mSGwgRapWubKP5ctLtzx54fywlm8jU0VFTRx?= =?us-ascii?Q?tZ3FwV0wXEpF8dxKmCmFKe04qR0v5EtAV3haYfbLrp9BhO16fPjFAu5Tfd84?= =?us-ascii?Q?WOmPO1O1kFUGEa2Uc2S9tq1o3oBiUUvPstTicxhs0FMp262QzF1KpZLmmLnE?= =?us-ascii?Q?8Q=3D=3D?= X-MS-Exchange-CrossTenant-Network-Message-Id: 9db6147f-544e-4cbe-0894-08dd3036dff3 X-MS-Exchange-CrossTenant-AuthSource: PH8PR11MB8107.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Jan 2025 22:50:40.1479 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: qqlumFY77oyh/p2TBoAPWFKgBjmTE/ymuDMt/qA8d4tzz82CfgRNGQ1ER5+8qEqEmSVx3h6N9ZI/6uVtlxC2fEhrnvl/X3GUnweMJiCAvH0= X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA3PR11MB8120 X-OriginatorOrg: intel.com Alistair Popple wrote: > Several functions internal to FS DAX use the following pattern when > trying to obtain an unlocked entry: > > xas_for_each(&xas, entry, end_idx) { > if (dax_is_locked(entry)) > entry = get_unlocked_entry(&xas, 0); > > 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