xfs: check return codes when flushing block devices

If a blkdev_issue_flush fails, fsync needs to report that to upper
levels.  Modify xfs_file_fsync to capture the errors, while trying to
flush as much data and log updates to disk as possible.

If log writes cannot flush the data device, we need to shut down the log
immediately because we've violated a log invariant.  Modify this code to
check the return value of blkdev_issue_flush as well.

This behavior seems to go back to about 2.6.15 or so, which makes this
fixes tag a bit misleading.

Link: https://elixir.bootlin.com/linux/v2.6.15/source/fs/xfs/xfs_vnodeops.c#L1187
Fixes: b5071ada

 ("xfs: remove xfs_blkdev_issue_flush")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>