Hillf Danton [off-list ref] wrote:

quoted

+	smp_store_release(&buf->meta.head, head);

Add a line of comment for the paring smp_load_acquire().
I did not find it in 04/11.

You won't find smp_load_acquire() - it's not in the kernel, though if you look
in the sample, you'll find the corresponding barrier in userspace.  Note that
there's a further implicit barrier you don't see.

I've added the comments:

	/* Barrier against userspace, ordering data read before tail read */
	ring_tail = READ_ONCE(buf->meta.tail);

and:

	/* Barrier against userspace, ordering head update after data write. */
	smp_store_release(&buf->meta.head, head);

David