On Wed, Aug 06, 2025 at 11:34:57AM +0100, Pedro Falcato wrote: > On Tue, Aug 05, 2025 at 08:21:23PM +0100, Lorenzo Stoakes wrote: > > +cc Pedro > > > > On Tue, Aug 05, 2025 at 03:09:54PM -0400, Zi Yan wrote: > > > On 5 Aug 2025, at 15:00, Lorenzo Stoakes wrote: > > > > > > > On Tue, Aug 05, 2025 at 01:51:40PM -0400, Zi Yan wrote: > > > >> diff --git a/tools/testing/selftests/mm/vm_util.h > > > >> b/tools/testing/selftests/mm/vm_util.h > > > >> index c20298ae98ea..b55d1809debc 100644 > > > >> --- a/tools/testing/selftests/mm/vm_util.h > > > >> +++ b/tools/testing/selftests/mm/vm_util.h > > > >> @@ -23,7 +23,7 @@ > > > >> * anything with it in order to trigger a read page fault. We > > > >> therefore must use > > > >> * volatile to stop the compiler from optimising this away. > > > >> */ > > > >> -#define FORCE_READ(x) (*(volatile typeof(x) *)x) > > > >> +#define FORCE_READ(x) (*(const volatile typeof(x) *)&(x)) > > > > > > > > NIT: but wonder if const is necessary, and also (as discussed off-list > > > > > > I just used READ_ONCE() code, but it is not necessary. > > > > It's not end of the world though. > > > > > > > > > again :) will this work with a (void) prefixed, just to a. make it clear > > > > we're reading but discarding and b. to avoid any possible compiler > > > > warning > > > > on this? > > > > > > Adding (void) makes no difference, at least from godbolt. > > > > I disagree with adding (void), because volatile being properly propagated into > the type should hide any Wunused-value warnings (because volatile reads can > have > side effects, so discarding a read is most definitely valid).
Yeah, I just wondered _why_. I mean this is fine as-is. I believe Andrew's already taken the patch as a hotfix anyway. > > And as I was seeing in https://godbolt.org/z/jnWsET1vx yesterday, GCC (and > clang) > can silently drop the volatile qualifier For Some Reason. Ack, would love to know why, but don't have the time to explore so was hoping you/someone else could figure it out and tell me :P > > -- > Pedro Cheers, Lorenzo
