Re: [RFC PATCH v2 11/31] kvx: Add atomic/locking headers

Hi Mark, On Fri, Jan 20, 2023 at 03:18:48PM +0000, Mark Rutland wrote: > On Fri, Jan 20, 2023 at 03:09:42PM +0100, Yann Sionneau wrote: > > +#define ATOMIC64_RETURN_OP(op, c_op) \ > > +static inline long arch_atomic64_##op##_return(long i, atomic64_t *v) \ > > +{ \ > > + long new, old, ret; \ > > + \ > > + do { \ > > + old = v->counter; \ > > This should be arch_atomic64_read(v), in order to avoid the potential for the > compiler to replay the access and introduce ABA races and other such problems. Thanks for the suggestion, this will be into v3. > For details, see: > > https://lore.kernel.org/lkml/Y70SWXHDmOc3RhMd@osiris/ > https://lore.kernel.org/lkml/Y71LoCIl+IFdy9D8@FVFF77S0Q05N/ > > I see that the generic 32-bit atomic code suffers from that issue, and we > should fix it. I took a look at the generic 32-bit atomic, but I am unsure if this needs to be done for both the SMP and non-SMP implementations. But I can send a first patch and we can discuss from there.

> > +static inline int arch_atomic_add_return(int i, atomic_t *v) > > +{ > > + int new, old, ret; > > + > > + do { > > + old = v->counter; > > Likewise, arch_atomic64_read(v) here. ack, this will bt arch_atomic_read(v) here since this is not atomic64_t here.