[PATCH 5.4 02/17] iomap: iomap that extends beyond EOF should be marked dirty

Chandan Babu R
2022-09-21T03:24:30Z

From: Dave Chinner <dchinner@redhat.com>

commit 7684e2c4384d5d1f884b01ab8bff2369e4db0bff upstream.

When doing a direct IO that spans the current EOF, and there are
written blocks beyond EOF that extend beyond the current write, the
only metadata update that needs to be done is a file size extension.

However, we don't mark such iomaps as IOMAP_F_DIRTY to indicate that
there is IO completion metadata updates required, and hence we may
fail to correctly sync file size extensions made in IO completion
when O_DSYNC writes are being used and the hardware supports FUA.

Hence when setting IOMAP_F_DIRTY, we need to also take into account
whether the iomap spans the current EOF. If it does, then we need to
mark it dirty so that IO completion will call generic_write_sync()
to flush the inode size update to stable storage correctly.

Fixes: 3460cac1ca76 ("iomap: Use FUA for pure data O_DSYNC DIO writes")
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
[darrick: removed the ext4 part; they'll handle it separately]
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Acked-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandan.babu@oracle.com>
---
fs/xfs/xfs_iomap.c | 7 +++++++
include/linux/iomap.h | 2 ++
2 files changed, 9 insertions(+)

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 239c9548b156..26cf811f3d96 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -1055,6 +1055,13 @@ xfs_file_iomap_begin(
trace_xfs_iomap_alloc(ip, offset, length, XFS_DATA_FORK, &imap);

out_finish:
+ /*
+ * Writes that span EOF might trigger an IO size update on completion,
+ * so consider them to be dirty for the purposes of O_DSYNC even if
+ * there is no other metadata changes pending or have been made here.
+ */
+ if ((flags & IOMAP_WRITE) && offset + length > i_size_read(inode))
+ iomap->flags |= IOMAP_F_DIRTY;
return xfs_bmbt_to_iomap(ip, iomap, &imap, shared);

out_found:
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 53b16f104081..74e05e7b67f5 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -32,6 +32,8 @@ struct vm_fault;
*
* IOMAP_F_DIRTY indicates the inode has uncommitted metadata needed to access
* written data and requires fdatasync to commit them to persistent storage.
+ * This needs to take into account metadata changes that *may* be made at IO
+ * completion, such as file size updates from direct IO.
*/
#define IOMAP_F_NEW 0x01 /* blocks have been newly allocated */
#define IOMAP_F_DIRTY 0x02 /* uncommitted metadata */
--
2.35.1