On Sun, May 22, 2016 at 09:50:40PM +0300, Alexey Dobriyan wrote:
> On Sun, May 22, 2016 at 12:48:27PM +0200, Peter Zijlstra wrote:
> > On Sat, May 21, 2016 at 11:14:49PM +0300, Alexey Dobriyan wrote:
> > > lockless_dereference() is supposed to take pointer not integer.
> >
> > Urgh :/
> >
> > Is there any way we can make lockless_dereference() issue a warning if
> > we don't feed it a pointer?
> >
> > Would something like so work? All pointer types should silently cast to
> > void * while integer (and others) should refuse to.
>
> This works (and spammy enough in case of seqlock, which is good)
> but not for "unsigned long":
>
> include/linux/percpu-refcount.h:146:36: warning: initialization makes
> pointer from integer without a cast [-Wint-conversion]
> percpu_ptr = lockless_dereference(ref->percpu_count_ptr);
TJ; would you prefer casting or not using lockless_dereference() here?
>
> > --- a/include/linux/compiler.h
> > +++ b/include/linux/compiler.h
> > @@ -544,6 +544,7 @@ static __always_inline void __write_once_size(volatile
> > void *p, void *res, int s
> > */
> > #define lockless_dereference(p) \
> > ({ \
> > + __maybe_unused void * _________p2 = p; \
> > typeof(p) _________p1 = READ_ONCE(p); \
> > smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
> > (_________p1); \
