default or selected kernelversion does not have config value CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP.
Result is shown for kernelversion 6.4.14

Slow down RCU grace-period cleanup to expose races


Linux Kernel Configuration
└─>RCU Debugging
└─>Slow down RCU grace-period cleanup to expose races
In linux kernel since version 4.1 (release Date: 2015-06-21)  
This option delays grace-period cleanup for a few jiffies
between cleaning up each pair of consecutive rcu_node
structures. This helps to expose races involving grace-period
cleanup, in other words, it makes your kernel less stable.
It can also greatly increase grace-period latency, especially
on systems with large numbers of CPUs. This is useful when
torture-testing RCU, but in almost no other circumstance.

Say Y here if you want your system to crash and hang more often.
Say N if you want a sane system.