Documentation: circular-buffers: use READ_ONCE()

While the {READ,WRITE}_ONCE() macros should be used in preference to
ACCESS_ONCE(), the circular buffer documentation uses the latter
exclusively.

To point people in the right direction, and as a step towards the
eventual removal of ACCESS_ONCE(), update the documentation to use
READ_ONCE(), as ACCESS_ONCE() is only used in a reader context in the
circular buffer documentation.

Signed-off-by: Mark Rutland <[e-mail]>
Acked-by: David Howells <[e-mail]>
Acked-by: Paul E. McKenney <[e-mail]>
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/circular-buffers.txt

···
 
 	unsigned long head = buffer->head;
 	/* The spin_unlock() and next spin_lock() provide needed ordering. */
-	unsigned long tail = ACCESS_ONCE(buffer->tail);
+	unsigned long tail = READ_ONCE(buffer->tail);
 
 	if (CIRC_SPACE(head, tail, buffer->size) >= 1) {
 		/* insert one item into the buffer */
···
 the new item, and then it shall make sure the CPU has finished reading the item
 before it writes the new tail pointer, which will erase the item.
 
-Note the use of ACCESS_ONCE() and smp_load_acquire() to read the
+Note the use of READ_ONCE() and smp_load_acquire() to read the
 opposition index.  This prevents the compiler from discarding and
 reloading its cached value - which some compilers will do across
 smp_read_barrier_depends().  This isn't strictly needed if you can