Re: [PATCH bpf-next 3/3] bpf, libbpf: use proper barriers in perf ring buffer walk

[Peter Zijlstra]

On Wed, Oct 17, 2018 at 04:41:56PM +0200, Daniel Borkmann wrote:
> +static __u64 bpf_perf_read_head(struct perf_event_mmap_page *header)
> +{
> +     __u64 data_head = READ_ONCE(header->data_head);
> +
> +     smp_rmb();
> +     return data_head;
> +}
> +
> +static void bpf_perf_write_tail(struct perf_event_mmap_page *header,
> +                             __u64 data_tail)
> +{
> +     smp_mb();
> +     header->data_tail = data_tail;
> +}

Same coments, either smp_load_acquire()/smp_store_release() or at the
very least a WRITE_ONCE() there.