Clear roots when retrying due to stale btree blocks.

Before deltas were added this code path was correct, but with
deltas we can't just retry this without clearing &root, since
it would potentially double count.

The condition where this could happen is when there are deltas in
several finalized log trees, and we've made progress towards reading
some of them, and then encounter a stale btree block. The retry
would not clear the collected trees, apply the same delta as was
already applied before the retry, and thus double count.

Signed-off-by: Auke Kok <auke.kok@versity.com>

kmod/src/wkic.c

@@ -886,8 +886,12 @@ retry_stale:
 	trace_scoutfs_wkic_read_items(sb, key, &start, &end);
 	ret = scoutfs_block_check_stale(sb, ret, &saved, &roots.fs_root.ref, &roots.logs_root.ref);
 	if (ret < 0) {
-		if (ret == -ESTALE)
+		if (ret == -ESTALE) {
+			/* not safe to retry due to delta items, must restart clean */
+			free_item_tree(&root);
+			root = RB_ROOT;
 			goto retry_stale;
+		}
 		goto out;
 	}