privilege/privileges: don't reuse chunk in loadTable function (#6976) (…

…#6986)

privilege/privileges/cache.go

@@ -183,16 +183,19 @@ func (p *MySQLPrivilege) loadTable(sctx sessionctx.Context, sql string,
  defer terror.Call(rs.Close)
 
  fs := rs.Fields()
- chk := rs.NewChunk()
- it := chunk.NewIterator4Chunk(chk)
  for {
+ // NOTE: decodeTableRow decodes data from a chunk Row, that is a shallow copy.
+ // The result will reference memory in the chunk, so the chunk must not be reused
+ // here, otherwise some werid bug will happen!
+ chk := rs.NewChunk()
  err = rs.Next(context.TODO(), chk)
  if err != nil {
  return errors.Trace(err)
  }
  if chk.NumRows() == 0 {
  return nil
  }
+ it := chunk.NewIterator4Chunk(chk)
  for row := it.Begin(); row != it.End(); row = it.Next() {
  err = decodeTableRow(row, fs)
  if err != nil {