Re: [patch V4 part 1 06/36] compiler: Simple READ/WRITE_ONCE() implementations

Peter Zijlstra
2020-05-06T15:37:15Z

On Wed, May 06, 2020 at 02:33:33PM +0100, Will Deacon wrote:
> On Tue, May 05, 2020 at 03:16:08PM +0200, Thomas Gleixner wrote:
> > READ/WRITE_ONCE_NOCHECK() is required for atomics in code which cannot be
> > instrumented like the x86 int3 text poke code. As READ/WRITE_ONCE() is
> > undergoing a rewrite, provide __{READ,WRITE}_ONCE_SCALAR().
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> > ---
> > include/linux/compiler.h | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> >
> > --- a/include/linux/compiler.h
> > +++ b/include/linux/compiler.h
> > @@ -313,6 +313,14 @@ unsigned long read_word_at_a_time(const
> > __u.__val; \
> > })
> >
> > +#define __READ_ONCE_SCALAR(x) \
> > + (*(const volatile typeof(x) *)&(x))
> > +
> > +#define __WRITE_ONCE_SCALAR(x, val) \
> > +do { \
> > + *(volatile typeof(x) *)&(x) = val; \
> > +} while (0)
>
> FWIW, these end up being called __READ_ONCE() and __WRITE_ONCE() after
> the rewrite; the *_SCALAR() variants will call into kcsan_check_atomic_*().
>
> If you go with that naming now, then any later conflict should fall out in
> the wash.

Ah excellent, clearly we had slightly different resoltions vs kcsan.
Thanks!