blkdev_issue_flush() can fail; make sure the error gets properly
propagated.
This is a port of the equivalent jbd patch from commit 
349ecd6a3c0e.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
        if (!err)
                err = err2;
        /* Make sure all replayed data is on permanent storage */
-       if (journal->j_flags & JBD2_BARRIER)
-               blkdev_issue_flush(journal->j_fs_dev, GFP_KERNEL, NULL);
+       if (journal->j_flags & JBD2_BARRIER) {
+               err2 = blkdev_issue_flush(journal->j_fs_dev, GFP_KERNEL, NULL);
+               if (!err)
+                       err = err2;
+       }
        return err;
 }