On Wed, Nov 16, 2016 at 11:12:49AM +0000, Mark Rutland wrote:
> 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 <mark.rutland@xxxxxxx>
> Cc: David Howells <dhowells@xxxxxxxxxx>
> Cc: Jonathan Corbet <corbet@xxxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> Cc: linux-doc@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> ---
> Documentation/circular-buffers.txt | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/circular-buffers.txt b/Documentation/circular-buffers.txt
> index 88951b1..4a824d2 100644
> --- a/Documentation/circular-buffers.txt
> +++ b/Documentation/circular-buffers.txt
> @@ -161,7 +161,7 @@ The producer will look something like this:
>
> 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 */
> @@ -222,7 +222,7 @@ This will instruct the CPU to make sure the index is up to date before reading
> 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
> --
> 1.9.1
>
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