c
bool is_ra_valid(struct file_ra_state *ra) {
    // Implement a check to ensure ra is valid and not freed
    // This could involve checking against a list of valid pointers or other application-specific logic
    return /* result of validity check */;
}

// In the main function:
if (is_ra_valid(ra)) {
    pgoff_t mark = index + ra->size - ra->async_size;
} else {
    // Handle invalid ra
    return -EINVAL;
}
