On Sun, Jan 26, 2020 at 10:29 AM Pavel Machek <pavel@xxxxxxx> wrote: > > > > - po->rollover->history[prandom_u32() % ROLLOVER_HLEN] = rxhash; > > + victim = prandom_u32() % ROLLOVER_HLEN; > > + > > + /* Avoid dirtying the cache line if possible */ > > + if (READ_ONCE(history[victim]) != rxhash) > > + WRITE_ONCE(history[victim], rxhash); > > + > > Replacing simple asignment with if() is ... not nice and with all the > "volatile" magic in _ONCE macros may not be win for > everyone. [Actually, I don't think this is win here. This is not > exactly hot path, is it? This is a critical hot path, eg under DDOS attack. > > If this is going to get more common, should we get > WRITE_ONCE_NONDIRTY() macro hiding the uglyness? > Sure, but we do not add macros for stable patches, usually. Honestly, WRITE_ONCE_NONDIRTY() looks ugly to me. Note that the KCSAN race might be solved in another way when data_race() is available.
