rcu: Document unique-name limitation for DEFINE_STATIC_SRCU()

	}

/*

 * define and init a srcu struct at build time.

 * dont't call init_srcu_struct() nor cleanup_srcu_struct() on it.

 * Define and initialize a srcu struct at build time.

 * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.

 *

 * Note that although DEFINE_STATIC_SRCU() hides the name from other

 * files, the per-CPU variable rules nevertheless require that the

 * chosen name be globally unique.  These rules also prohibit use of

 * DEFINE_STATIC_SRCU() within a function.  If these rules are too

 * restrictive, declare the srcu_struct manually.  For example, in

 * each file:

 *

 *	static struct srcu_struct my_srcu;

 *

 * Then, before the first use of each my_srcu, manually initialize it:

 *

 *	init_srcu_struct(&my_srcu);

 *

 * See include/linux/percpu-defs.h for the rules on per-CPU variables.

 */

#define __DEFINE_SRCU(name, is_static)					\

	static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\