bcachefs: Fix a transaction path overflow

It turns out we need bch2_extent_trim_atomi() even when we're deleting
extents one at a time because it's possible for one reflink_p to
reference arbitrarily many reflink_v extents. This doesn't normally
happen, but the data move path can fragment existing extents in the
background.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/inode.c

@@ -599,7 +599,6 @@ static int bch2_inode_delete_keys(struct btree_trans *trans,
 	 * iterator:
 	 */
 	bch2_trans_iter_init(trans, &iter, id, POS(inum.inum, 0),
-			     BTREE_ITER_NOT_EXTENTS|
 			     BTREE_ITER_INTENT);
 
 	while (1) {
@@ -622,6 +621,14 @@ static int bch2_inode_delete_keys(struct btree_trans *trans,
 		bkey_init(&delete.k);
 		delete.k.p = iter.pos;
 
+		if (iter.flags & BTREE_ITER_IS_EXTENTS) {
+			bch2_key_resize(&delete.k, k.k->p.offset - iter.pos.offset);
+
+			ret = bch2_extent_trim_atomic(trans, &iter, &delete);
+			if (ret)
+				goto err;
+		}
+
 		ret = bch2_trans_update(trans, &iter, &delete, 0) ?:
 		      bch2_trans_commit(trans, NULL, NULL,
 					BTREE_INSERT_NOFAIL);