[PATCH 01/14] iomap: iomap that extends beyond EOF should be marked dirty

Christoph Hellwig
2019-10-17T17:56:34Z

From: Dave Chinner <dchinner@redhat.com>

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.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/ext4/inode.c | 9 ++++++++-
fs/xfs/xfs_iomap.c | 7 +++++++
include/linux/iomap.h | 2 ++
3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 516faa280ced..e9dc52537e5b 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3523,9 +3523,16 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
return ret;
}

+ /*
+ * 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 being made or are pending here.
+ */
iomap->flags = 0;
- if (ext4_inode_datasync_dirty(inode))
+ if (ext4_inode_datasync_dirty(inode) ||
+ offset + length > i_size_read(inode))
iomap->flags |= IOMAP_F_DIRTY;
+
iomap->bdev = inode->i_sb->s_bdev;
iomap->dax_dev = sbi->s_daxdev;
iomap->offset = (u64)first_block << blkbits;
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index f780e223b118..32993c2acbd9 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -1049,6 +1049,13 @@ 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 7aa5d6117936..24bd227d59f9 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 */
--
2.20.1