file_systems_string
struct file_systems_string *old;
old = rcu_replace_pointer(file_systems_string, NULL,
struct file_systems_string *old, *new;
new = kmalloc(offsetof(struct file_systems_string, string) + newlen + 1,
old = file_systems_string;
rcu_assign_pointer(file_systems_string, new);
struct file_systems_string *fss;
fss = rcu_dereference(file_systems_string);
static struct file_systems_string __read_mostly __rcu *file_systems_string;