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Message-ID: <20250805175140.241656-1-ziy@nvidia.com>
Date: Tue, 5 Aug 2025 13:51:40 -0400
From: Zi Yan <ziy@...dia.com>
To: wang lian <lianux.mm@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-mm@...ck.org
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
David Hildenbrand <david@...hat.com>,
Wei Yang <richard.weiyang@...il.com>,
Christian Brauner <brauner@...nel.org>,
Jann Horn <jannh@...gle.com>,
Kairui Song <ryncsn@...il.com>,
Liam Howlett <liam.howlett@...cle.com>,
Mark Brown <broonie@...nel.org>,
SeongJae Park <sj@...nel.org>,
Shuah Khan <shuah@...nel.org>,
Vlastimil Babka <vbabka@...e.cz>,
linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org,
Zi Yan <ziy@...dia.com>
Subject: [PATCH] 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.
Fixes: 3f6bfd4789a0 ("selftests/mm: reuse FORCE_READ to replace "asm volatile("" : "+r" (XXX));"")
Signed-off-by: Zi Yan <ziy@...dia.com>
---
FORCE_READ() comes from commit 876320d71f51 ("selftests/mm: add self tests for
guard page feature"). I will a separate patch to stable tree.
tools/testing/selftests/mm/cow.c | 4 ++--
tools/testing/selftests/mm/guard-regions.c | 2 +-
tools/testing/selftests/mm/hugetlb-madvise.c | 4 +++-
tools/testing/selftests/mm/migration.c | 2 +-
tools/testing/selftests/mm/pagemap_ioctl.c | 2 +-
tools/testing/selftests/mm/split_huge_page_test.c | 7 +++++--
tools/testing/selftests/mm/vm_util.h | 2 +-
7 files changed, 14 insertions(+), 9 deletions(-)
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 718daceb5282..3c761228e451 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -440,8 +440,11 @@ 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;
--
2.47.2
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