ext4: iomap that extends beyond EOF should be marked dirty

This patch addresses what Dave Chinner had discovered and fixed within
commit: 7684e2c4384d. This changes does not have any user visible
impact for ext4 as none of the current users of ext4_iomap_begin()
that extend files depend on IOMAP_F_DIRTY.

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: Matthew Bobrowski <mbobrowski@mbobrowski.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/8b43ee9ee94bee5328da56ba0909b7d2229ef150.1572949325.git.mbobrowski@mbobrowski.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index f33fa86fff6788b297ad905c367a9b481e5e673a..b422d9b8c0bd7b95e8f81fef874fa0f25635beae 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3565,8 +3565,14 @@ retry:
                        return ret;
        }
 
+       /*
+        * Writes that span EOF might trigger an I/O 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;