On 5 Aug 2025, at 14:38, Jann Horn wrote: > On Tue, Aug 5, 2025 at 7:51 PM Zi Yan <z...@nvidia.com> wrote: >> FORCE_READ() converts input value x to its pointer type then reads from >> address x. This is wrong. If x is a non-pointer, it would be caught it >> easily. But all FORCE_READ() callers are trying to read from a pointer and >> FORCE_READ() basically reads a pointer to a pointer instead of the original >> typed pointer. Almost no access violation was found, except the one from >> split_huge_page_test. > [...] >> 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)) > > So is the problem with the old code basically that it should have been > something like > > #define FORCE_READ(x) (*(volatile typeof(*(x)) *)(x)) > > to actually cast the normal pointer to a volatile pointer?
Yeah. That works too. I would rename it to FORCE_READ_PTR to avoid misuse. :) Best Regards, Yan, Zi
