On Tue, Feb 04, 2025 at 02:00:23PM +1030, Qu Wenruo wrote: > [BUG] > It is a long known bug that VM image on btrfs can lead to data csum > mismatch, if the qemu is using direct-io for the image (this is commonly > known as cache mode none). > > [CAUSE] > Inside the VM, if the fs is EXT4 or XFS, or even NTFS from Windows, the > fs is allowed to dirty/modify the folio even the folio is under > writeback (as long as the address space doesn't have AS_STABLE_WRITES > flag inherited from the block device). Btw, can you add an xfstests that reproduces this by modifying pages under direct I/O? That would be really helpful to verify the code when we want to turn back on real direct I/O eventually when the VM is fixed to prevent the modifications.
