On 10/09/2018 17:44, Emilio G. Cota wrote: > On Mon, Sep 10, 2018 at 01:32:15 +0200, Paolo Bonzini wrote: >> On 03/09/2018 19:18, Emilio G. Cota wrote: >>> Using atomics here is a mistake since they're not guaranteed >>> to compile. >> >> But isn't it technically a C11 data race if you don't use atomics? > > Yes, it's undefined behaviour. > >> Could we make nocheck read/set degrade to just a volatile access when >> used on a variable that is bigger than pointers, or perhaps always >> except when using tsan? > > But volatile wouldn't save you from undefined behaviour, would it?
Yeah, but 1) only on those hosts that cannot do CONFIG_ATOMIC64 2) we pretty much already define what we expect from volatile. Paolo > A simpler and definitely correct alternative is to just use a > spinlock instead of the seqlock also for reads when !CONFIG_ATOMIC64. > We don't care about scalability on those rare hosts anyway, so > I'd go with that. > > Thanks, > > Emilio >
