fix: remove auto-close GetObjectReader (#12009)

locks can get relinquished when Read() sees io.EOF
leading to prematurely closing of the readers

concurrent writes on the same object can have
undesired consequences here when these locks
are relinquished.

pkg/s3select/select.go

@@ -1,5 +1,5 @@
 /*
- * MinIO Cloud Storage, (C) 2019 MinIO, Inc.
+ * MinIO Cloud Storage, (C) 2019-2021 MinIO, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -216,6 +216,7 @@ type S3Select struct {
 	statement      *sql.SelectStatement
 	progressReader *progressReader
 	recordReader   recordReader
+	close          func() error
 }
 
 var (
@@ -311,6 +312,7 @@ func (s3Select *S3Select) Open(getReader func(offset, length int64) (io.ReadClos
 			}
 			return err
 		}
+		s3Select.close = rc.Close
 		return nil
 	case jsonFormat:
 		rc, err := getReader(0, -1)
@@ -333,6 +335,8 @@ func (s3Select *S3Select) Open(getReader func(offset, length int64) (io.ReadClos
 		} else {
 			s3Select.recordReader = json.NewReader(s3Select.progressReader, &s3Select.Input.JSONArgs)
 		}
+
+		s3Select.close = rc.Close
 		return nil
 	case parquetFormat:
 		if !strings.EqualFold(os.Getenv("MINIO_API_SELECT_PARQUET"), "on") {
@@ -396,6 +400,12 @@ func (s3Select *S3Select) marshal(buf *bytes.Buffer, record sql.Record) error {
 
 // Evaluate - filters and sends records read from opened reader as per select statement to http response writer.
 func (s3Select *S3Select) Evaluate(w http.ResponseWriter) {
+	defer func() {
+		if s3Select.close != nil {
+			s3Select.close()
+		}
+	}()
+
 	getProgressFunc := s3Select.getProgress
 	if !s3Select.Progress.Enabled {
 		getProgressFunc = nil