commit 0f9160b4 upstream.

Now that truncate locks out new page faults, we no longer need to do
special writeback hacks in truncate to work around potential races
between page faults, page cache truncation and file size updates to
ensure we get write page faults for extending truncates on sub-page
block size filesystems. Hence we can remove the code in
xfs_setattr_size() that handles this and update the comments around
the code tha thandles page cache truncate and size updates to
reflect the new reality.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
[bwh: Backported to 3.16: we never had the previous hack, so just update the
 comment]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>