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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?35fN8T/k5Y3o5sq7mvnk0dP1iGGnEhPPPWVB8/NMM+d/EFC4f5ZLgfcsy/U1?= =?us-ascii?Q?VtGuAgVyIvnDHjrxRWiNpPFr8S9FIxt0uPJhl51qAC2jzZvuvQ+Y7HSVaLAV?= =?us-ascii?Q?ypbJpFpU3GsHxNm8SZG6qtZY2jgbvAhYRhuCjTw3sOKkZfjw+Hpq043Woy7T?= =?us-ascii?Q?HRdqq/ooeG4zlgXsVqreVJmCeuH2+8OiM8ZtaeMNfxPdkCTVU300T8VKN40s?= =?us-ascii?Q?Wvr6NtbeDQLfU7mXW6L2gXM/lIq5b6a0obprb/59mq9ABN+BO9ezHlzXPPuc?= =?us-ascii?Q?8mG4JDRQU2k0rEMskeFKU8UFHmMFKpbhSAxFHe9kYXta8Sht/OeNWmsGoVtM?= =?us-ascii?Q?O+Oc6J/KRHaXN1j/hksRG66PpmT3SY/5c7RufA0YIsTuO8kLiDXdvVzWUHDD?= =?us-ascii?Q?YkiWeB0wNkprTxr0B8S+BTHQKwubweesvA2YDhlvbUmGYzZZCk1xAffRjjV8?= =?us-ascii?Q?HviDNH3hXYXvqznk+2y/aA6XsgxYeM4fiX1XskDOJ4edYPZq5jBtibcCF70C?= =?us-ascii?Q?SRDK1uCPh3/KSQa1ltkcUYVQFk9EImkZGOp/0XIzLuF5gVQ5ki9WLJNyRrYc?= =?us-ascii?Q?YUvQrwRNuj1w6QVDZXv9IetdDzbWaOQaBIx1PpZ+JSjAnqJsoazKUYDsCVre?= =?us-ascii?Q?RVbl0CpU34EmJ6Av5ZU0mHBAa1qr4xhMz+XLyFx8cvqgbm/priREpeGJ93IR?= =?us-ascii?Q?LLiI3p9kVtnJeEKCbYCStjk174IZ2p/NuyIX1Bj1ZhbodNWBACf96OxjYopk?= =?us-ascii?Q?gzfNUnER9/nXi/6L1HBSVZ9VyhiMPVb6G4J+yQyrWTo0vajtq3Ny0yjScgu7?= =?us-ascii?Q?pDNMyiIYWFFDcx0KkWbEG1w9I1HwOi76Iq3m1kDnxAvZpThQYdvUjIkDiuEK?= =?us-ascii?Q?w9xjBVWoVEz0Drg5lxNdFNK23+25GAE0bI1fUjjENibJ/WKkqEeTqZt4oetP?= =?us-ascii?Q?74xI/aLacHbDTmJ1dxt7TdoQzU0iuK6Nxrt8PJEb7bugK79iAZbv8LRJIrVu?= =?us-ascii?Q?+p8mJ1Y9cgYTV5Fep9RuldR7+tOyygxN7ogP+8YsFM9PQh/SsTnj6TBEOyj3?= =?us-ascii?Q?z8MwMXFC9ewNzNfcAWqxHd/x8+8wPqH/NB28Chnmmm1O1yb9CltjdlLP2Bdk?= =?us-ascii?Q?I/5eK22My6BAE2K2R71J9DdwIRjlKhhs3+ykASMSfhktPebyEYb5Km0AJ6xf?= =?us-ascii?Q?IBAlAJQTa5mIu5uIInVAGoO1lwXziJWwClflknLw2l+sBaa5J/6DG3/s0CMC?= =?us-ascii?Q?/AYHdRzRP0MI9k96BtRtC/CREJ3DD7RotPNqmHxofRji/iYM498KAAZOEbbs?= =?us-ascii?Q?BtVJfDlXPQHNa5IWEB5CexgJ1cqt0vbHxpoklrrWgtLUggutvO8DRwM4qfmx?= =?us-ascii?Q?fpsubyArVgZrMU43Dy5mg9JGk1hSm2O3ghAdR6g8yikUy3pLy99m4Y1Fu2Ox?= =?us-ascii?Q?5edbKbr6pmFBni8VbAnojIXppeIRnpSqJCncimgAhp11pOBFWxJCE2mJMApv?= =?us-ascii?Q?dAMOQmPUJ9qrI2FKzKgdTcHHbN09iOs9epwwKFOGJKk/C1EkkD3RRdMyK9ZC?= =?us-ascii?Q?2833AszuUro2NRGDqy/xPFnKqNedArIOntl20Yi1?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: ee6690a8-e45d-4ee6-67c7-08da9d60b279 X-MS-Exchange-CrossTenant-AuthSource: MN2PR12MB4192.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 23 Sep 2022 12:39:46.5099 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 90q0ZUzVI3GS7GaB7BSUrqvZUR7OMJ0qqyEnsKp2DsX8oZ6Dqji3SnBZOzhH0fgm X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY8PR12MB7657 On Fri, Sep 23, 2022 at 12:10:12PM +1000, Dave Chinner wrote: > > Jason mentioned a scenario here: > > > > https://lore.kernel.org/all/YyuoE8BgImRXVkkO@nvidia.com/ > > > > Multi-thread process where thread1 does open(O_DIRECT)+mmap()+read() and > > thread2 does memunmap()+close() while the read() is inflight. > > And, ah, what production application does this and expects to be > able to process the result of the read() operation without getting a > SEGV? The read() will do GUP and get a pined page, next the memunmap()/close will release the inode the VMA was holding open. The read() FD is NOT a DAX FD. We are now UAFing the DAX storage. There is no SEGV. It is not about sane applications, it is about kernel security against hostile userspace. > i.e. The underlying problem here is that memunmap() frees the VMA > while there are still active task-based references to the pages in > that VMA. IOWs, the VMA should not be torn down until the O_DIRECT > read has released all the references to the pages mapped into the > task address space. This is Jan's suggestion, I think we are still far from being able to do that for O_DIRECT paths. Even if you fix the close() this way, doesn't truncate still have the same problem? At the end of the day the rule is a DAX page must not be re-used until its refcount is 0. At some point the FS should wait for. Jason