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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5 Aug 2025, at 14:38, Jann Horn wrote: > On Tue, Aug 5, 2025 at 7:51=E2=80=AFPM Zi Yan 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 a= nd >> FORCE_READ() basically reads a pointer to a pointer instead of the origi= nal >> 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/selfte= sts/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