On Thu, 21 May 2020 at 11:47, Marco Elver <el...@google.com> wrote:
>
> On Fri, 15 May 2020 at 17:04, Marco Elver <el...@google.com> wrote:
> >
> > The volatile access no longer needs to be wrapped in data_race(),
> > because we require compilers that emit instrumentation distinguishing
> > volatile accesses.
> >
> > Signed-off-by: Marco Elver <el...@google.com>
> > ---
> > include/linux/compiler.h | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> > index 17c98b215572..fce56402c082 100644
> > --- a/include/linux/compiler.h
> > +++ b/include/linux/compiler.h
> > @@ -229,7 +229,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f,
> > int val,
> > #define __READ_ONCE_SCALAR(x) \
> > ({ \
> > typeof(x) *__xp = &(x); \
> > - __unqual_scalar_typeof(x) __x = data_race(__READ_ONCE(*__xp)); \
> > + __unqual_scalar_typeof(x) __x = __READ_ONCE(*__xp); \
> > kcsan_check_atomic_read(__xp, sizeof(*__xp)); \
>
> Some self-review: We don't need kcsan_check_atomic anymore, and this
> should be removed.
>
> I'll send v2 to address this (together with fix to data_race()
> removing nested statement expressions).
The other thing here is that we no longer require __xp, and can just
pass x into __READ_ONCE.
> > smp_read_barrier_depends(); \
> > (typeof(x))__x; \
> > @@ -250,7 +250,7 @@ do {
> > \
> > do { \
> > typeof(x) *__xp = &(x); \
> > kcsan_check_atomic_write(__xp, sizeof(*__xp)); \
>
> Same.
__xp can also be removed.
Note that this effectively aliases __WRITE_ONCE_SCALAR to
__WRITE_ONCE. To keep the API consistent with READ_ONCE, I assume we
want to keep __WRITE_ONCE_SCALAR, in case it is meant to change in
future?
> > - data_race(({ __WRITE_ONCE(*__xp, val); 0; })); \
> > + __WRITE_ONCE(*__xp, val); \
> > } while (0)
> >
> > #define WRITE_ONCE(x, val) \
> > --
> > 2.26.2.761.g0e0b3e54be-goog
> >
