Worked on the zephyrproject-rtos/zephyr repository to address a critical thread-safety issue in the Zephyr RTOS core, focusing on embedded systems and multi-threading with C programming. Improved the reliability of list length calculations by removing a static loop iterator from the Z_GENLIST_LEN macro, ensuring that the loop variable is stack-allocated and preventing data corruption during concurrent thread and ISR execution. This change restored reentrancy to the sys_*_len functions, reducing the risk of incorrect list lengths or infinite loops. The work included clear documentation of the non-reentrant behavior, contributing to better maintainability and code quality in embedded deployments.