2026-01-21, 13:16:35 +0200, Ido Schimmel wrote:
> On Tue, Jan 20, 2026 at 05:21:28PM +0800, David Yang wrote:
> > On 64bit arches, struct u64_stats_sync is empty and provides no help
> > against load/store tearing. memcpy() should not be considered atomic
> > against u64 values. Use u64_stats_copy() instead.
>
> The existing memcpy() does seem problematic (even if in practice it's
> not) and the proposed solution in patch #1 seems OK to me given that all
> the callers only pass structures containing 64 bit counters. Couldn't
> find any more instances of this pattern.
No direct instances using memcpy, but do we need to also full structs
copied within a u64_stats_fetch_begin/u64_stats_fetch_retry loop?
// net/mpls/af_mpls.c
static void mpls_get_stats(struct mpls_dev *mdev,
struct mpls_link_stats *stats)
{
[...]
for_each_possible_cpu(i) {
struct mpls_link_stats local;
unsigned int start;
p = per_cpu_ptr(mdev->stats, i);
do {
start = u64_stats_fetch_begin(&p->syncp);
local = p->stats;
} while (u64_stats_fetch_retry(&p->syncp, start));
[...]
// net/openvswitch/datapath.c
static void get_dp_stats(const struct datapath *dp, struct ovs_dp_stats *stats,
struct ovs_dp_megaflow_stats *mega_stats)
{
[...]
for_each_possible_cpu(i) {
const struct dp_stats_percpu *percpu_stats;
struct dp_stats_percpu local_stats;
unsigned int start;
percpu_stats = per_cpu_ptr(dp->stats_percpu, i);
do {
start = u64_stats_fetch_begin(&percpu_stats->syncp);
local_stats = *percpu_stats;
} while (u64_stats_fetch_retry(&percpu_stats->syncp, start));
[...]
And if not: can't we just use the same pattern for those other cases
that this series is touching?
--
Sabrina
