Linux 7.2-rc7 Restores Btrfs Fixup Workers to Address Silent Data Loss
Linux 7.2 briefly removed Btrfs’s copy-on-write fixup mechanism under the assumption that newer memory-management behavior made it unnecessary. That assumption was wrong: dirty pages without an ordered extent could escape the filesystem’s COW handling and cause silent data loss. The fixup worker infrastructure—more than 600 lines, including updated folio and subpage support—has been restored for rc7.
This is a reminder that filesystem correctness mechanisms often encode assumptions that are difficult to see from adjacent MM changes. The restoration also includes fixes for an encoded-ioctl leak and unsafe large-folio configurations.