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Tue, 8 Sep 2026 17:19:41 +0000 Received: from IA0PR12MB8374.namprd12.prod.outlook.com ([fe80::d85f:4c87:ae84:3f16]) by IA0PR12MB8374.namprd12.prod.outlook.com ([fe80::d85f:4c87:ae84:3f16%5]) with mapi id 15.21.0406.005; Tue, 8 Sep 2026 17:19:40 +0000 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Tue, 08 Sep 2026 13:19:38 -0400 Message-Id: From: "Zi Yan" Subject: Re: [PATCH v3 08/14] erofs: use folio_attach/detach_private() instead of direct assignment Cc: , , "Gao Xiang" , "Chao Yu" , "Yue Hu" , "Jeffle Xu" , "Sandeep Dhavale" , "Hongbo Li" , "Chunhai Guo" , To: "David Hildenbrand (Arm)" , "Matthew Wilcox (Oracle)" , "Andrew Morton" , "Muchun Song" , "Lorenzo Stoakes" , "Liam R. 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But after PG_priva= te >> is replaced by checking folio->private in a future commit, it can break >> folio_expected_ref_count(), since the folio has private data without >> elevated refcount. Change them to use folio_attach/detach_private(). > > Freezing the folio will properly work I assume, as we'd always freeze wit= h that > refcount in mind or remove the reference (detach private) early? Yes. > > I'm thinking of folio_ref_freeze() in __folio_freeze_and_split_unmapped()= . > > Or is the ref only very short-lived either way such that we don't care? The folios here are locked since they are in the process of readahead, which requires all folios locked. So they are not reachable from folio split code. In additio, the private is deatched and ref is decreased before the folio lock is dropped. --=20 Best Regards, Yan, Zi