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

[Peter Zijlstra]

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@xxxxxxxxxxxxx>
> > Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > ---
> >  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!