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, 6 insertions, 88 deletions

diff --git a/fs/bcachefs/data_update.c b/fs/bcachefs/data_update.c
index ae7e60d6e583..c89ee14f8b6b 100644
--- a/fs/bcachefs/data_update.c
+++ b/fs/bcachefs/data_update.c
@@ -16,81 +16,6 @@
 #include "subvolume.h"
 #include "trace.h"
 
-static int 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 iter, iter2;
-	struct bkey_s_c k, k2;
-	snapshot_id_list s;
-	struct bkey_i *update;
-	int ret;
-
-	if (!btree_type_has_snapshots(id))
-		return 0;
-
-	darray_init(&s);
-
-	if (!bch2_snapshot_has_children(c, old_pos.snapshot))
-		return 0;
-
-	bch2_trans_iter_init(trans, &iter, id, old_pos,
-			     BTREE_ITER_NOT_EXTENTS|
-			     BTREE_ITER_ALL_SNAPSHOTS);
-	while (1) {
-		k = bch2_btree_iter_prev(&iter);
-		ret = bkey_err(k);
-		if (ret)
-			break;
-
-		if (!k.k)
-			break;
-
-		if (!bkey_eq(old_pos, k.k->p))
-			break;
-
-		if (bch2_snapshot_is_ancestor(c, k.k->p.snapshot, old_pos.snapshot) &&
-		    !snapshot_list_has_ancestor(c, &s, k.k->p.snapshot)) {
-			struct bpos whiteout_pos = new_pos;
-
-			whiteout_pos.snapshot = k.k->p.snapshot;
-
-			k2 = bch2_bkey_get_iter(trans, &iter2, id, whiteout_pos,
-						BTREE_ITER_NOT_EXTENTS|
-						BTREE_ITER_INTENT);
-			ret = bkey_err(k2);
-
-			if (!ret && k2.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, &iter2, update,
-							BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE);
-			}
-			bch2_trans_iter_exit(trans, &iter2);
-
-			if (ret)
-				break;
-
-			ret = snapshot_list_add(c, &s, k.k->p.snapshot);
-			if (ret)
-				break;
-		}
-	}
-	bch2_trans_iter_exit(trans, &iter);
-	darray_exit(&s);
-
-	return ret;
-}
-
 static void trace_move_extent_finish2(struct bch_fs *c, struct bkey_s_c k)
 {
 	if (trace_move_extent_finish_enabled()) {
@@ -327,19 +252,12 @@ restart_drop_extra_replicas:
 
 		next_pos = insert->k.p;
 
-		if (!bkey_eq(bkey_start_pos(&insert->k), bkey_start_pos(k.k))) {
-			ret = insert_snapshot_whiteouts(trans, m->btree_id, k.k->p,
-							bkey_start_pos(&insert->k));
-			if (ret)
-				goto err;
-		}
-
-		if (!bkey_eq(insert->k.p, k.k->p)) {
-			ret = insert_snapshot_whiteouts(trans, m->btree_id,
-							k.k->p, insert->k.p);
-			if (ret)
-				goto err;
-		}
+		ret =   bch2_insert_snapshot_whiteouts(trans, m->btree_id,
+						k.k->p, bkey_start_pos(&insert->k)) ?:
+			bch2_insert_snapshot_whiteouts(trans, m->btree_id,
+						k.k->p, insert->k.p);
+		if (ret)
+			goto err;
 
 		ret   = bch2_trans_update(trans, &iter, insert,
 				BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE) ?: