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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 Jun 2025 09:38:44.2355 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: c47d7c57-05cb-4dfa-466b-08ddad82c07e X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: DB3PEPF0000885F.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DBBPR08MB10650 On 17/06/25 2:56 pm, David Hildenbrand wrote: > On 17.06.25 11:18, Dev Jain wrote: >> >> On 17/06/25 1:17 pm, David Hildenbrand wrote: >>> On 17.06.25 07:10, Dev Jain wrote: >>>> >>>> On 26/05/25 12:05 pm, Dev Jain wrote: >>>>> Hello all, >>>>> >>>>> After doing an xas_load() and xas_retry(), we take neither a >>>>> reference nor a lock >>>>> on the folio, and we do an xas_reload(). Is this just to reduce the >>>>> time window >>>>> for a race? >>>>> >>>>> If the above is true, then, there is a negligible window between >>>>> xas_load() and >>>>> xas_reload(), because only xas_retry() exists between them, so why >>>>> to even reload()? >>>>> >>>>> Thanks, >>>>> Dev >>>> >>>> I do not completely remember our discussion in THP Cabal; I recall >>>> David Howells maybe >>>> saying that the folios are already locked, so it is safe to do >>>> xas_load and then do >>>> a folio_get()? Even if we remove the redundant xas_reload(), I still >>>> don't understand >>>> why we won't need xas_reload() at least after folio_get()? >>> >>> I think the points where >>> >>> (a) this should go all away soon >>> >>> (b) there is the expectation that the folios cannot get truncated >>>      concurrently. So we can do an unconditional folio_get(), don't >>> have >>>      to check folio->mapping etc. >> >> Well...pretty sure the file read path is taking the inode->i_rwsem or >> i_lock somewhere, >> >> to synchronize with truncation/reclaim, can't figure out where. Reclaim >> takes the i_lock in __remove_mapping and >> >> then freezes the folio reference, so the read path must lock i_lock >> somewhere. > > I mean, if concurrent freeing of a folio would be possible, the > function would be horribly broken :) Yes, trusting the kernel overlords I have dropped my search : )