xfs: punch out data fork delalloc blocks on COW writeback failure

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2039058 Tested: full xfstests and xfs/542 Conflicts: xfs_is_shutdown() is replaced with XFS_FORCED_SHUTDOW()

commit 5ca5916b6bc93577c360c06cb7cdf71adb9b5faf Author: Brian Foster bfoster@redhat.com Date: Thu, 21 Oct 2021 14:11:55 -0700

xfs: punch out data fork delalloc blocks on COW writeback failure

If writeback I/O to a COW extent fails, the COW fork blocks are punched out and the data fork blocks left alone. It is possible for COW fork blocks to overlap non-shared data fork blocks (due to cowextsz hint prealloc), however, and writeback unconditionally maps to the COW fork whenever blocks exist at the corresponding offset of the page undergoing writeback. This means it's quite possible for a COW fork extent to overlap delalloc data fork blocks, writeback to convert and map to the COW fork blocks, writeback to fail, and finally for ioend completion to cancel the COW fork blocks and leave stale data fork delalloc blocks around in the inode. The blocks are effectively stale because writeback failure also discards dirty page state.

If this occurs, it is likely to trigger assert failures, free space accounting corruption and failures in unrelated file operations. For example, a subsequent reflink attempt of the affected file to a new target file will trip over the stale delalloc in the source file and fail. Several of these issues are occasionally reproduced by generic/648, but are reproducible on demand with the right sequence of operations and timely I/O error injection.

To fix this problem, update the ioend failure path to also punch out underlying data fork delalloc blocks on I/O error. This is analogous to the writeback submission failure path in xfs_discard_page() where we might fail to map data fork delalloc blocks and consistent with the successful COW writeback completion path, which is responsible for unmapping from the data fork and remapping in COW fork blocks.

Fixes: 787eb485 ("xfs: fix and streamline error handling in xfs_end_io") Signed-off-by: Brian Foster bfoster@redhat.com Reviewed-by: Darrick J. Wong djwong@kernel.org Signed-off-by: Darrick J. Wong djwong@kernel.org

Signed-off-by: Andrey Albershteyn aalbersh@redhat.com