docs: RCU: Convert rcuref.txt to ReST

   whatisRCU

   rcu

   rculist_nulls

   rcuref

   torture

   listRCU

   NMI-RCU

Reference-count design for elements of lists/arrays protected by RCU.

.. SPDX-License-Identifier: GPL-2.0

====================================================================

Reference-count design for elements of lists/arrays protected by RCU

====================================================================

Please note that the percpu-ref feature is likely your first

Reference counting on elements of lists which are protected by traditional

reader/writer spinlocks or semaphores are straightforward:

CODE LISTING A:

CODE LISTING A::

    1.					    2.

    add()				    search_and_reference()

    {					    {

has already been deleted from the list/array.  Use atomic_inc_not_zero()

in this scenario as follows:

CODE LISTING B:

CODE LISTING B::

    1.					    2.

    add()				    search_and_reference()

    {					    {

atomic_dec_and_test() may be moved from delete() to el_free()

as follows:

CODE LISTING C:

CODE LISTING C::

    1.					    2.

    add()				    search_and_reference()

    {					    {

modern computer systems, even the small ones.

In cases where delete() can sleep, synchronize_rcu() can be called from

delete(), so that el_free() can be subsumed into delete as follows:

delete(), so that el_free() can be subsumed into delete as follows::

    4.

    delete()