Re: [PATCH] compiler.h: simplify data_race() macro

From: Marco Elver
Date: Mon Jun 24 2024 - 10:41:58 EST


On Mon, 24 Jun 2024 at 16:38, Alexey Dobriyan <adobriyan@xxxxxxxxx> wrote:
>
> On Mon, Jun 24, 2024 at 02:27:43PM +0200, Marco Elver wrote:
> > On Mon, 24 Jun 2024 at 13:49, Alexey Dobriyan <adobriyan@xxxxxxxxx> wrote:
> > >
> > > Use auto type deduction and comma expression to decrease macro expansion
> > > size.
> > >
> > > __unqual_scalar_typeof() is quite wordy macro by itself.
> > >
> > > "expr" can be arbitrary complex so not expanding it twice is good.
> > > Should be faster too because type is deduced only once
> > > from the initializer.
> > >
> > > Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
> >
> > Thanks for cleaning up. That code certainly predates the availability
> > of __auto_type. Although if I recall correctly, __unqual_scalar_typeof
> > became the first user of _Generic (the first C11 keyword we used in
> > the kernel?), but we used some ifdef to still support ancient
> > compilers initially (that definitely also didn't have __auto_type).
> >
> > Reviewed-by: Marco Elver <elver@xxxxxxxxxx>
> >
> > Which tree is this for?
>
> This is against mainline. Should not really matter, -next has the same code.

I meant which maintainer/tree should pick this up?

> > > --- a/include/linux/compiler.h
> > > +++ b/include/linux/compiler.h
> > > @@ -200,10 +200,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
> > > */
> > > #define data_race(expr) \
> > > ({ \
> > > - __unqual_scalar_typeof(({ expr; })) __v = ({ \
> > > - __kcsan_disable_current(); \
> > > - expr; \
> > > - }); \
> > > + __auto_type __v = (__kcsan_disable_current(), expr); \
> > > __kcsan_enable_current(); \
> > > __v; \
> > > })