+ selftests-mm-fix-unused-variable-warnings-in-hugetlb-madvisec-migrationc.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: selftests/mm: fix unused variable warnings in hugetlb-madvise.c, migration.c
has been added to the -mm mm-unstable branch.  Its filename is
     selftests-mm-fix-unused-variable-warnings-in-hugetlb-madvisec-migrationc.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-mm-fix-unused-variable-warnings-in-hugetlb-madvisec-migrationc.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: John Hubbard <jhubbard@nvidia.com>
Subject: selftests/mm: fix unused variable warnings in hugetlb-madvise.c, migration.c
Date: Fri, 2 Jun 2023 19:15:49 -0700

Dummy variables are required in order to make these two (similar)
routines work, so in both cases, declare the variables as volatile in
order to avoid the clang compiler warning.

Furthermore, in order to ensure that each test actually does what is
intended, add an asm volatile invocation (thanks to David Hildenbrand
for the suggestion), with a clarifying comment so that it survives
future maintenance.

Link: https://lkml.kernel.org/r/20230603021558.95299-3-jhubbard@nvidia.com
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/mm/hugetlb-madvise.c |    8 ++++++--
 tools/testing/selftests/mm/migration.c       |    5 ++++-
 2 files changed, 10 insertions(+), 3 deletions(-)

--- a/tools/testing/selftests/mm/hugetlb-madvise.c~selftests-mm-fix-unused-variable-warnings-in-hugetlb-madvisec-migrationc
+++ a/tools/testing/selftests/mm/hugetlb-madvise.c
@@ -65,11 +65,15 @@ void write_fault_pages(void *addr, unsig
 
 void read_fault_pages(void *addr, unsigned long nr_pages)
 {
-	unsigned long dummy = 0;
+	volatile unsigned long dummy = 0;
 	unsigned long i;
 
-	for (i = 0; i < nr_pages; i++)
+	for (i = 0; i < nr_pages; i++) {
 		dummy += *((unsigned long *)(addr + (i * huge_page_size)));
+
+		/* Prevent the compiler from optimizing out the entire loop: */
+		asm volatile("" : "+r" (dummy));
+	}
 }
 
 int main(int argc, char **argv)
--- a/tools/testing/selftests/mm/migration.c~selftests-mm-fix-unused-variable-warnings-in-hugetlb-madvisec-migrationc
+++ a/tools/testing/selftests/mm/migration.c
@@ -95,12 +95,15 @@ int migrate(uint64_t *ptr, int n1, int n
 
 void *access_mem(void *ptr)
 {
-	uint64_t y = 0;
+	volatile uint64_t y = 0;
 	volatile uint64_t *x = ptr;
 
 	while (1) {
 		pthread_testcancel();
 		y += *x;
+
+		/* Prevent the compiler from optimizing out the writes to y: */
+		asm volatile("" : "+r" (y));
 	}
 
 	return NULL;
_

Patches currently in -mm which might be from jhubbard@nvidia.com are

selftests-mm-fix-uffd-stress-unused-function-warning.patch
selftests-mm-fix-unused-variable-warnings-in-hugetlb-madvisec-migrationc.patch
selftests-mm-fix-warning-expression-which-evaluates-to-zero-in-mlock2-testsc.patch
selftests-mm-fix-invocation-of-tests-that-are-run-via-shell-scripts.patch
selftests-mm-gitignore-add-mkdirty-va_high_addr_switch.patch
selftests-mm-fix-two-wformat-security-warnings-in-uffd-builds.patch
selftests-mm-fix-a-possibly-uninitialized-warning-in-pkey-x86h.patch
selftests-mm-fix-uffd-unit-testsc-build-failure-due-to-missing-madv_collapse.patch
selftests-mm-move-psize-pshift-into-vm_utilsc.patch
selftests-mm-move-uffd-routines-from-vm_utilc-to-uffd-commonc.patch
documentation-kselftest-make-headers-is-a-prerequisite.patch
selftests-error-out-if-kernel-header-files-are-not-yet-built.patch