extent scan: don't serialize dedupe and LOGICAL_INO when using extent scan mode

The serialization doesn't seem to be necessary for the extent scan mode.
No infinite loops in the kernel have been observed in the past two years,
despite never having used MultiLock for the extent scanner.

Leave the serialization for now on the subvol scanners.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>

src/bees.cc

@@ -797,6 +797,13 @@ bees_main(int argc, char *argv[])
 	// Set root scan mode
 	bc->roots()->set_scan_mode(root_scan_mode);
 
+	if (root_scan_mode == BeesRoots::SCAN_MODE_EXTENT) {
+		MultiLocker::enable_locking(false);
+	} else {
+		// Workaround for a kernel bug that the subvol-based crawlers keep triggering
+		MultiLocker::enable_locking(true);
+	}
+
 	// Start crawlers
 	bc->start();