[13/45] xfs: refine the unaligned check for always COW inodes in xfs_file_dio_write

Commit Message

Christoph Hellwig Feb. 18, 2025, 8:10 a.m. UTC

For always COW inodes we also must check the alignment of each individual
iovec segment, as they could end up with different I/Os due to the way
bio_iov_iter_get_pages works, and we'd then overwrite an already written
block.  The existing always_cow sysctl based code doesn't catch this
because nothing enforces that blocks aren't rewritten, but for zoned XFS
on sequential write required zones this is a hard error.

Signed-off-by: Christoph Hellwig <[e-mail]>
Reviewed-by: "Darrick J. Wong" <[e-mail]>
---
 fs/xfs/xfs_file.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

Patch

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 785f6bbf1406..d88a771d4c23 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -721,7 +721,16 @@  xfs_file_dio_write(
 	/* direct I/O must be aligned to device logical sector size */
 	if ((iocb->ki_pos | count) & target->bt_logical_sectormask)
 		return -EINVAL;
-	if ((iocb->ki_pos | count) & ip->i_mount->m_blockmask)
+
+	/*
+	 * For always COW inodes we also must check the alignment of each
+	 * individual iovec segment, as they could end up with different
+	 * I/Os due to the way bio_iov_iter_get_pages works, and we'd
+	 * then overwrite an already written block.
+	 */
+	if (((iocb->ki_pos | count) & ip->i_mount->m_blockmask) ||
+	    (xfs_is_always_cow_inode(ip) &&
+	     (iov_iter_alignment(from) & ip->i_mount->m_blockmask)))
 		return xfs_file_dio_write_unaligned(ip, iocb, from);
 	return xfs_file_dio_write_aligned(ip, iocb, from);
 }