gfs2: Issue message when revokes cannot be written

Before this patch, function gfs2_ail_empty_gl would silently return an
error to the caller. This would get silently set into sd_log_error which
would cause a withdraw, but there was no indication why the file system
was withdrawn. This patch adds a fs_err to log the appropriate error
message.
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/glops.c

@@ -124,8 +124,10 @@ static int gfs2_ail_empty_gl(struct gfs2_glock *gl)
 	memset(&tr, 0, sizeof(tr));
 	set_bit(TR_ONSTACK, &tr.tr_flags);
 	ret = __gfs2_trans_begin(&tr, sdp, 0, revokes, _RET_IP_);
-	if (ret)
+	if (ret) {
+		fs_err(sdp, "Transaction error %d: Unable to write revokes.", ret);
 		goto flush;
+	}
 	__gfs2_ail_flush(gl, 0, revokes);
 	gfs2_trans_end(sdp);