Re: [PATCH v3 08/14] erofs: use folio_attach/detach_private() instead of direct assignment

On Wed Sep 9, 2026 at 9:27 AM EDT, David Hildenbrand (Arm) wrote:

On 9/8/26 19:19, Zi Yan wrote:

quoted

On Tue Sep 8, 2026 at 12:13 PM EDT, David Hildenbrand (Arm) wrote:

quoted

On 9/8/26 04:56, Zi Yan wrote:

quoted

erofs_onlinefolio_init/split/end() use folio->private without setting
PG_private or increasing folio refcount and it works. But after PG_private
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 with that
refcount in mind or remove the reference (detach private) early?

Yes.

quoted

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.

It would be great to summarize this interaction with core-mm (migration/split)
in the patch description.

Will update the commit message.



-- 
Best Regards,
Yan, Zi