bcachefs: Fix corruption with writeable snapshots

When partially overwriting an extent in an older snapshot, the existing
extent has to be split.

If the existing extent was overwritten in a different (sibling)
snapshot, we have to ensure that the split won't be visible in the
sibling snapshot.

data_update.c already has code for this,
bch2_insert_snapshot_writeouts() - we just need to move it into
btree_update_leaf.c and change bch2_trans_update_extent() to use it as
well.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

1 files changed, 70 insertions, 3 deletions

diff --git a/fs/bcachefs/btree_update_leaf.c b/fs/bcachefs/btree_update_leaf.c
index 33693467810b..25d73db9adc6 100644
--- a/fs/bcachefs/btree_update_leaf.c
+++ b/fs/bcachefs/btree_update_leaf.c
@@ -1343,6 +1343,69 @@ static int need_whiteout_for_snapshot(struct btree_trans *trans,
 
 	return ret;
 }
+
+int __bch2_insert_snapshot_whiteouts(struct btree_trans *trans,
+				   enum btree_id id,
+				   struct bpos old_pos,
+				   struct bpos new_pos)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_iter old_iter, new_iter;
+	struct bkey_s_c old_k, new_k;
+	snapshot_id_list s;
+	struct bkey_i *update;
+	int ret;
+
+	if (!bch2_snapshot_has_children(c, old_pos.snapshot))
+		return 0;
+
+	darray_init(&s);
+
+	bch2_trans_iter_init(trans, &old_iter, id, old_pos,
+			     BTREE_ITER_NOT_EXTENTS|
+			     BTREE_ITER_ALL_SNAPSHOTS);
+	while ((old_k = bch2_btree_iter_prev(&old_iter)).k &&
+	       !(ret = bkey_err(old_k)) &&
+	       bkey_eq(old_pos, old_k.k->p)) {
+		struct bpos whiteout_pos =
+			SPOS(new_pos.inode, new_pos.offset, old_k.k->p.snapshot);;
+
+		if (!bch2_snapshot_is_ancestor(c, old_k.k->p.snapshot, old_pos.snapshot) ||
+		    snapshot_list_has_ancestor(c, &s, old_k.k->p.snapshot))
+			continue;
+
+		new_k = bch2_bkey_get_iter(trans, &new_iter, id, whiteout_pos,
+					   BTREE_ITER_NOT_EXTENTS|
+					   BTREE_ITER_INTENT);
+		ret = bkey_err(new_k);
+		if (ret)
+			break;
+
+		if (new_k.k->type == KEY_TYPE_deleted) {
+			update = bch2_trans_kmalloc(trans, sizeof(struct bkey_i));
+			ret = PTR_ERR_OR_ZERO(update);
+			if (ret)
+				break;
+
+			bkey_init(&update->k);
+			update->k.p		= whiteout_pos;
+			update->k.type		= KEY_TYPE_whiteout;
+
+			ret = bch2_trans_update(trans, &new_iter, update,
+						BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE);
+		}
+		bch2_trans_iter_exit(trans, &new_iter);
+
+		ret = snapshot_list_add(c, &s, old_k.k->p.snapshot);
+		if (ret)
+			break;
+	}
+	bch2_trans_iter_exit(trans, &old_iter);
+	darray_exit(&s);
+
+	return ret;
+}
+
 int bch2_trans_update_extent(struct btree_trans *trans,
 			     struct btree_iter *orig_iter,
 			     struct bkey_i *insert,
@@ -1396,8 +1459,10 @@ int bch2_trans_update_extent(struct btree_trans *trans,
 
 			bch2_cut_back(start, update);
 
-			ret = bch2_btree_insert_nonextent(trans, btree_id, update,
-						  BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE|flags);
+			ret =   bch2_insert_snapshot_whiteouts(trans, btree_id,
+						k.k->p, update->k.p) ?:
+				bch2_btree_insert_nonextent(trans, btree_id, update,
+						BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE|flags);
 			if (ret)
 				goto err;
 		}
@@ -1411,7 +1476,9 @@ int bch2_trans_update_extent(struct btree_trans *trans,
 			bch2_cut_front(start, update);
 			bch2_cut_back(insert->k.p, update);
 
-			ret = bch2_btree_insert_nonextent(trans, btree_id, update,
+			ret =   bch2_insert_snapshot_whiteouts(trans, btree_id,
+						k.k->p, update->k.p) ?:
+				bch2_btree_insert_nonextent(trans, btree_id, update,
 						  BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE|flags);
 			if (ret)
 				goto err;