ktest.pl: Prevent recursion of default variable options

If a default variable contains itself, do not recurse on it.

For example:

  ADD_CONFIG := ${CONFIG_DIR}/temp_config
  DEFAULTS
  ADD_CONFIG = ${CONFIG_DIR}/default_config ${ADD_CONFIG}

The above works because the temp variable ADD_CONFIG (is a temp because it
is created with ":=") is already defined, it will be substituted in the
variable option. But if it gets commented out:

  # ADD_CONFIG := ${CONFIG_DIR}/temp_config
  DEFAULTS
  ADD_CONFIG = ${CONFIG_DIR}/default_config ${ADD_CONFIG}

Then the above will go into a recursive loop where ${ADD_CONFIG} will
get replaced with the current definition of ADD_CONFIG which contains the
${ADD_CONFIG} and that will also try to get converted. ktest.pl will error
after 100 attempts of recursion and fail.

When replacing a variable with the default variable, if the default
variable contains itself, do not replace it.

Cc: "John Warthog9 Hawley" <[email protected]>
Cc: Dhaval Giani <[email protected]>
Cc: Greg KH <[email protected]>
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Steven Rostedt <[email protected]>

Author: rostedt

tools/testing/ktest/ktest.pl

@@ -1394,7 +1394,10 @@ sub __eval_option {
 	# If a variable contains itself, use the default var
 	if (($var eq $name) && defined($opt{$var})) {
 	    $o = $opt{$var};
-	    $retval = "$retval$o";
+	    # Only append if the default doesn't contain itself
+	    if ($o !~ m/\$\{$var\}/) {
+		$retval = "$retval$o";
+	    }
 	} elsif (defined($opt{$o})) {
 	    $o = $opt{$o};
 	    $retval = "$retval$o";