Re: [PATCH v9 07/22] tracing: Add lock-free tracing_map

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Jul 16, 2015 at 12:22:40PM -0500, Tom Zanussi wrote:
> +	for (i = 0; i < elt->map->n_fields; i++) {
> +		atomic64_set(&dup_elt->fields[i].sum,
> +			     atomic64_read(&elt->fields[i].sum));
> +		dup_elt->fields[i].cmp_fn = elt->fields[i].cmp_fn;
> +	}
> +
> +	return dup_elt;
> +}

So there is a lot of atomic64_{set,read}() in this patch set, what kind
of magic properties do you assume they have?

Note that atomic*_{set,read}() are weaker than {WRITE,READ}_ONCE(), so
if you're assuming they do that, you're mistaken -- although it is on a
TODO list someplace to go fix that.