Make install.db read only in mtr

This ensures that no mtr test can change install.db after it's initial
creation as changing it while as another thread is coping it will lead to
failures in at least InnoDB and Aria recovery.

Fixed spider/bugfix.mdev_30370 that was wrongly used install.db

mysql-test/lib/My/File/Path.pm

@@ -34,7 +34,7 @@ use strict;
 
 use Exporter;
 use base "Exporter";
-our @EXPORT= qw /rmtree mkpath copytree/;
+our @EXPORT= qw /rmtree mkpath copytree make_readonly/;
 
 use File::Find;
 use File::Copy;
@@ -184,6 +184,10 @@ sub copytree {
     # Only copy plain files
     next unless -f "$from_dir/$_";
     copy("$from_dir/$_", "$to_dir/$_");
+    if (!$use_umask)
+    {
+      chmod(0666, "$to_dir/$_");
+    }
   }
   closedir(DIR);
 
@@ -193,4 +197,29 @@ sub copytree {
   }
 }
 
+
+sub make_readonly {
+  my ($dir) = @_;
+
+  die "Usage: make_readonly(<dir>])"
+    unless @_ == 1;
+
+  opendir(DIR, "$dir")
+    or croak("Can't find $dir$!");
+  for(readdir(DIR)) {
+
+    next if "$_" eq "." or "$_" eq "..";
+
+    if ( -d "$dir/$_" )
+    {
+      make_readonly("$dir/$_");
+      next;
+    }
+
+    # Only copy plain files
+    next unless -f "$dir/$_";
+    chmod 0444, "$dir/$_";
+  }
+  closedir(DIR);
+}
 1;

mysql-test/lib/My/SafeProcess/Base.pm

@@ -40,7 +40,7 @@ our @EXPORT= qw(create_process);
 #   Retry a couple of times if fork returns EAGAIN
 #
 sub _safe_fork {
-  my $retries= 5;
+  my $retries= 100;
   my $pid;
 
  FORK:

mysql-test/mysql-test-run.pl

@@ -401,8 +401,11 @@ sub main {
   my $tests= collect_test_cases($opt_reorder, $opt_suites, \@opt_cases, \@opt_skip_test_list);
   mark_time_used('collect');
 
-  mysql_install_db(default_mysqld(), "$opt_vardir/install.db") unless using_extern();
-
+  if (!using_extern())
+  {
+    mysql_install_db(default_mysqld(), "$opt_vardir/install.db");
+    make_readonly("$opt_vardir/install.db");
+  }
   if ($opt_dry_run)
   {
     for (@$tests) {

storage/spider/mysql-test/spider/bugfix/t/mdev_30370.test

@@ -2,4 +2,7 @@
 --echo # MDEV-30370 mariadbd hangs when running with --wsrep-recover and --plugin-load-add=ha_spider.so
 --echo #
 
---exec $MYSQLD_BOOTSTRAP_CMD --wsrep-recover --plugin-load-add=ha_spider.so
+let $MYSQLD_DATADIR=$MYSQLTEST_VARDIR/mdev_30370;
+--mkdir $MYSQLD_DATADIR
+--exec $MYSQLD_BOOTSTRAP_CMD --wsrep-recover --plugin-load-add=ha_spider.so --datadir=$MYSQLD_DATADIR
+--rmdir $MYSQLD_DATADIR