On Thu, Jul 2, 2020 at 1:18 PM Will Deacon <will@xxxxxxxxxx> wrote:
> On Thu, Jul 02, 2020 at 12:08:41PM +0200, Arnd Bergmann wrote:
> > On Thu, Jul 2, 2020 at 11:48 AM Will Deacon <will@xxxxxxxxxx> wrote:
> > > On Thu, Jul 02, 2020 at 10:32:39AM +0100, Mark Rutland wrote:
> Not sure I follow you here, but I can confirm that what you're worried
> about doesn't happen for the usual case of a pointer-to-volatile scalar.
>
> For example, ignoring dependency ordering:
>
> unsigned long foo(volatile unsigned long *p)
> {
> return smp_load_acquire(p) + 1;
> }
>
> Ends up looking like:
>
> unsigned long ___p1 = *(const volatile unsigned long *)p;
> smp_mb();
> (volatile unsigned long)___p1;
>
> My understanding is that casting a non-pointer type to volatile doesn't
> do anything, so we're good.
Right, I mixed up the correct
(typeof(*p))___p;
with the incorrect
*typeof(p)&___p;
which would dereference a volatile pointer and cause the
problem.
The code is all fine then.
Arnd
