From: Zi Yan Date: Tue, 5 Aug 2025 17:51:40 +0000 (-0400) Subject: selftests/mm: fix FORCE_READ to read input value correctly X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=5bbc2b785e63699cfcaa7adbf739f6e9b771028a;p=linux-block.git selftests/mm: fix FORCE_READ to read input value correctly 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. Fix it by implementing a simplified READ_ONCE() instead. Link: https://lkml.kernel.org/r/20250805175140.241656-1-ziy@nvidia.com Fixes: 3f6bfd4789a0 ("selftests/mm: reuse FORCE_READ to replace "asm volatile("" : "+r" (XXX));"") Signed-off-by: Zi Yan Reviewed-by: Lorenzo Stoakes Acked-by: David Hildenbrand Reviewed-by: wang lian Reviewed-by: Wei Yang Cc: Christian Brauner Cc: Jann Horn Cc: Kairui Song Cc: Liam Howlett Cc: Mark Brown Cc: SeongJae Park Cc: Shuah Khan Cc: Vlastimil Babka Cc: Zi Yan Signed-off-by: Andrew Morton --- diff --git a/tools/testing/selftests/mm/cow.c b/tools/testing/selftests/mm/cow.c index d30625c18259..c744c603d688 100644 --- a/tools/testing/selftests/mm/cow.c +++ b/tools/testing/selftests/mm/cow.c @@ -1554,8 +1554,8 @@ static void run_with_zeropage(non_anon_test_fn fn, const char *desc) } /* Read from the page to populate the shared zeropage. */ - FORCE_READ(mem); - FORCE_READ(smem); + FORCE_READ(*mem); + FORCE_READ(*smem); fn(mem, smem, pagesize); munmap: diff --git a/tools/testing/selftests/mm/guard-regions.c b/tools/testing/selftests/mm/guard-regions.c index b0d42eb04e3a..8dd81c0a4a5a 100644 --- a/tools/testing/selftests/mm/guard-regions.c +++ b/tools/testing/selftests/mm/guard-regions.c @@ -145,7 +145,7 @@ static bool try_access_buf(char *ptr, bool write) if (write) *ptr = 'x'; else - FORCE_READ(ptr); + FORCE_READ(*ptr); } signal_jump_set = false; diff --git a/tools/testing/selftests/mm/hugetlb-madvise.c b/tools/testing/selftests/mm/hugetlb-madvise.c index 1afe14b9dc0c..c5940c0595be 100644 --- a/tools/testing/selftests/mm/hugetlb-madvise.c +++ b/tools/testing/selftests/mm/hugetlb-madvise.c @@ -50,8 +50,10 @@ void read_fault_pages(void *addr, unsigned long nr_pages) unsigned long i; for (i = 0; i < nr_pages; i++) { + unsigned long *addr2 = + ((unsigned long *)(addr + (i * huge_page_size))); /* Prevent the compiler from optimizing out the entire loop: */ - FORCE_READ(((unsigned long *)(addr + (i * huge_page_size)))); + FORCE_READ(*addr2); } } diff --git a/tools/testing/selftests/mm/migration.c b/tools/testing/selftests/mm/migration.c index c5a73617796a..ea945eebec2f 100644 --- a/tools/testing/selftests/mm/migration.c +++ b/tools/testing/selftests/mm/migration.c @@ -110,7 +110,7 @@ void *access_mem(void *ptr) * the memory access actually happens and prevents the compiler * from optimizing away this entire loop. */ - FORCE_READ((uint64_t *)ptr); + FORCE_READ(*(uint64_t *)ptr); } return NULL; diff --git a/tools/testing/selftests/mm/pagemap_ioctl.c b/tools/testing/selftests/mm/pagemap_ioctl.c index 0d4209eef0c3..e6face7c0166 100644 --- a/tools/testing/selftests/mm/pagemap_ioctl.c +++ b/tools/testing/selftests/mm/pagemap_ioctl.c @@ -1525,7 +1525,7 @@ void zeropfn_tests(void) ret = madvise(mem, hpage_size, MADV_HUGEPAGE); if (!ret) { - FORCE_READ(mem); + FORCE_READ(*mem); ret = pagemap_ioctl(mem, hpage_size, &vec, 1, 0, 0, PAGE_IS_PFNZERO, 0, 0, PAGE_IS_PFNZERO); diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c index 05de1fc0005b..44a3f8a58806 100644 --- a/tools/testing/selftests/mm/split_huge_page_test.c +++ b/tools/testing/selftests/mm/split_huge_page_test.c @@ -439,8 +439,11 @@ int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size, int *fd, } madvise(*addr, fd_size, MADV_HUGEPAGE); - for (size_t i = 0; i < fd_size; i++) - FORCE_READ((*addr + i)); + for (size_t i = 0; i < fd_size; i++) { + char *addr2 = *addr + i; + + FORCE_READ(*addr2); + } if (!check_huge_file(*addr, fd_size / pmd_pagesize, pmd_pagesize)) { ksft_print_msg("No large pagecache folio generated, please provide a filesystem supporting large folio\n"); 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)) extern unsigned int __page_size; extern unsigned int __page_shift;