Re: [PATCH net-next v2 4/7] net: openvswitch: fix load tearing with u64_stats
From: David Laight <hidden>
Date: 2026-01-26 18:29:31
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On Sat, 24 Jan 2026 00:21:36 +0800 David Yang [off-list ref] wrote:
On 64bit arches, struct u64_stats_sync is empty and provides no help against load/store tearing. struct copying should not be considered tear-free. Use u64_stats_reads() instead.
Except that the compiler doesn't ever generate 'tearing accesses' for aligned 64bit accesses on any 64bit architecture. Similarly memcpy() won't generate problematic accesses. The problem is purely theoretical - the C language lets the compiler split accesses, but it doesn't. David
quoted hunk ↗ jump to hunk
Signed-off-by: David Yang <mmyangfl@gmail.com> --- net/openvswitch/datapath.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c index d5b6e2002bc1..8ba94df7f942 100644 --- a/net/openvswitch/datapath.c +++ b/net/openvswitch/datapath.c@@ -770,7 +770,8 @@ static void get_dp_stats(const struct datapath *dp, struct ovs_dp_stats *stats, do { start = u64_stats_fetch_begin(&percpu_stats->syncp); - local_stats = *percpu_stats; + u64_stats_reads(&local_stats, percpu_stats, + sizeof(local_stats)); } while (u64_stats_fetch_retry(&percpu_stats->syncp, start)); stats->n_hit += local_stats.n_hit;