On Mon, 26 Jan 2026 19:35:38 +0100 Eric Dumazet <[email protected]> wrote:
> On Mon, Jan 26, 2026 at 7:29 PM David Laight > <[email protected]> wrote: > > > > On Sat, 24 Jan 2026 00:21:36 +0800 > > David Yang <[email protected]> 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. > > Yeah, although we still have races that KCSAN can detect. > > data_race() or READ_ONCE() would be necessary to avoid noisy KCSAN reports. > > While many KCSAN reports are boring, some of them point to real bugs. > Could something be put in u64_stats_fetch_begin() to stop KCSAN bleating? With the way READ_ONCE and WRITE_ONCE now get enforced I do wonder if some data shouldn't just be marked 'volatile'? That would give 'non-tearing' accesses, but without the inter-cpu ordering that (I think) READ/WRITE_ONCE also give. For stats counters that is enough. David _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
