Several mm selftests use the `asm volatile("" : "+r" (variable));`
construct to force a read of a variable, preventing the compiler from
optimizing away the memory access. This idiom is cryptic and duplicated
across multiple test files.
Following a suggestion from David[1], this patch refactors this
common pattern into a FORCE_READ() macro
[1] https://lore.kernel.org/lkml/4a3e0759-caa1-4cfa-bc3f-402593f1eee3@redhat.com/
Signed-off-by: wang lian <lianux.mm@gmail.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
tools/testing/selftests/mm/cow.c | 30 +++++++++----------
tools/testing/selftests/mm/guard-regions.c | 7 -----
tools/testing/selftests/mm/hugetlb-madvise.c | 5 +---
tools/testing/selftests/mm/migration.c | 13 ++++----
tools/testing/selftests/mm/pagemap_ioctl.c | 4 +--
.../selftests/mm/split_huge_page_test.c | 4 +--
tools/testing/selftests/mm/vm_util.h | 7 +++++
7 files changed, 31 insertions(+), 39 deletions(-)
diff --git a/tools/testing/selftests/mm/cow.c b/tools/testing/selftests/mm/cow.c
index 788e82b00b75..d30625c18259 100644
--- a/tools/testing/selftests/mm/cow.c
+++ b/tools/testing/selftests/mm/cow.c
@@ -1534,7 +1534,7 @@ static void test_ro_fast_pin(char *mem, const char *smem, size_t size)
static void run_with_zeropage(non_anon_test_fn fn, const char *desc)
{
- char *mem, *smem, tmp;
+ char *mem, *smem;
log_test_start("%s ... with shared zeropage", desc);
@@ -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. */
- tmp = *mem + *smem;
- asm volatile("" : "+r" (tmp));
+ FORCE_READ(mem);
+ FORCE_READ(smem);
fn(mem, smem, pagesize);
munmap:
@@ -1566,7 +1566,7 @@ static void run_with_zeropage(non_anon_test_fn fn, const char *desc)
static void run_with_huge_zeropage(non_anon_test_fn fn, const char *desc)
{
- char *mem, *smem, *mmap_mem, *mmap_smem, tmp;
+ char *mem, *smem, *mmap_mem, *mmap_smem;
size_t mmap_size;
int ret;
@@ -1617,8 +1617,8 @@ static void run_with_huge_zeropage(non_anon_test_fn fn, const char *desc)
* the first sub-page and test if we get another sub-page populated
* automatically.
*/
- tmp = *mem + *smem;
- asm volatile("" : "+r" (tmp));
+ FORCE_READ(mem);
+ FORCE_READ(smem);
if (!pagemap_is_populated(pagemap_fd, mem + pagesize) ||
!pagemap_is_populated(pagemap_fd, smem + pagesize)) {
ksft_test_result_skip("Did not get THPs populated\n");
@@ -1634,7 +1634,7 @@ static void run_with_huge_zeropage(non_anon_test_fn fn, const char *desc)
static void run_with_memfd(non_anon_test_fn fn, const char *desc)
{
- char *mem, *smem, tmp;
+ char *mem, *smem;
int fd;
log_test_start("%s ... with memfd", desc);
@@ -1668,8 +1668,8 @@ static void run_with_memfd(non_anon_test_fn fn, const char *desc)
}
/* Fault the page in. */
- tmp = *mem + *smem;
- asm volatile("" : "+r" (tmp));
+ FORCE_READ(mem);
+ FORCE_READ(smem);
fn(mem, smem, pagesize);
munmap:
@@ -1682,7 +1682,7 @@ static void run_with_memfd(non_anon_test_fn fn, const char *desc)
static void run_with_tmpfile(non_anon_test_fn fn, const char *desc)
{
- char *mem, *smem, tmp;
+ char *mem, *smem;
FILE *file;
int fd;
@@ -1724,8 +1724,8 @@ static void run_with_tmpfile(non_anon_test_fn fn, const char *desc)
}
/* Fault the page in. */
- tmp = *mem + *smem;
- asm volatile("" : "+r" (tmp));
+ FORCE_READ(mem);
+ FORCE_READ(smem);
fn(mem, smem, pagesize);
munmap:
@@ -1740,7 +1740,7 @@ static void run_with_memfd_hugetlb(non_anon_test_fn fn, const char *desc,
size_t hugetlbsize)
{
int flags = MFD_HUGETLB;
- char *mem, *smem, tmp;
+ char *mem, *smem;
int fd;
log_test_start("%s ... with memfd hugetlb (%zu kB)", desc,
@@ -1778,8 +1778,8 @@ static void run_with_memfd_hugetlb(non_anon_test_fn fn, const char *desc,
}
/* Fault the page in. */
- tmp = *mem + *smem;
- asm volatile("" : "+r" (tmp));
+ FORCE_READ(mem);
+ FORCE_READ(smem);
fn(mem, smem, hugetlbsize);
munmap:
diff --git a/tools/testing/selftests/mm/guard-regions.c b/tools/testing/selftests/mm/guard-regions.c
index 93af3d3760f9..4b76e72e7053 100644
--- a/tools/testing/selftests/mm/guard-regions.c
+++ b/tools/testing/selftests/mm/guard-regions.c
@@ -35,13 +35,6 @@
static volatile sig_atomic_t signal_jump_set;
static sigjmp_buf signal_jmp_buf;
-/*
- * Ignore the checkpatch warning, we must read from x but don't want to do
- * 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)
-
/*
* How is the test backing the mapping being tested?
*/
diff --git a/tools/testing/selftests/mm/hugetlb-madvise.c b/tools/testing/selftests/mm/hugetlb-madvise.c
index e74107185324..1afe14b9dc0c 100644
--- a/tools/testing/selftests/mm/hugetlb-madvise.c
+++ b/tools/testing/selftests/mm/hugetlb-madvise.c
@@ -47,14 +47,11 @@ void write_fault_pages(void *addr, unsigned long nr_pages)
void read_fault_pages(void *addr, unsigned long nr_pages)
{
- volatile unsigned long dummy = 0;
unsigned long 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));
+ FORCE_READ(((unsigned long *)(addr + (i * huge_page_size))));
}
}
diff --git a/tools/testing/selftests/mm/migration.c b/tools/testing/selftests/mm/migration.c
index a306f8bab087..c5a73617796a 100644
--- a/tools/testing/selftests/mm/migration.c
+++ b/tools/testing/selftests/mm/migration.c
@@ -16,6 +16,7 @@
#include <sys/types.h>
#include <signal.h>
#include <time.h>
+#include "vm_util.h"
#define TWOMEG (2<<20)
#define RUNTIME (20)
@@ -103,15 +104,13 @@ int migrate(uint64_t *ptr, int n1, int n2)
void *access_mem(void *ptr)
{
- 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));
+ /* Force a read from the memory pointed to by ptr. This ensures
+ * the memory access actually happens and prevents the compiler
+ * from optimizing away this entire loop.
+ */
+ 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 c2dcda78ad31..0d4209eef0c3 100644
--- a/tools/testing/selftests/mm/pagemap_ioctl.c
+++ b/tools/testing/selftests/mm/pagemap_ioctl.c
@@ -1525,9 +1525,7 @@ void zeropfn_tests(void)
ret = madvise(mem, hpage_size, MADV_HUGEPAGE);
if (!ret) {
- char tmp = *mem;
-
- asm volatile("" : "+r" (tmp));
+ 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 f0d9c035641d..05de1fc0005b 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -399,7 +399,6 @@ int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size, int *fd,
char **addr)
{
size_t i;
- int dummy = 0;
unsigned char buf[1024];
srand(time(NULL));
@@ -441,8 +440,7 @@ 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++)
- dummy += *(*addr + i);
- asm volatile("" : "+r" (dummy));
+ FORCE_READ((*addr + i));
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 2b154c287591..c20298ae98ea 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -18,6 +18,13 @@
#define PM_SWAP BIT_ULL(62)
#define PM_PRESENT BIT_ULL(63)
+/*
+ * Ignore the checkpatch warning, we must read from x but don't want to do
+ * 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)
+
extern unsigned int __page_size;
extern unsigned int __page_shift;
--
2.43.0On 17 Jul 2025, at 9:18, wang lian wrote:
> Several mm selftests use the `asm volatile("" : "+r" (variable));`
> construct to force a read of a variable, preventing the compiler from
> optimizing away the memory access. This idiom is cryptic and duplicated
> across multiple test files.
>
> Following a suggestion from David[1], this patch refactors this
> common pattern into a FORCE_READ() macro
>
> [1] https://lore.kernel.org/lkml/4a3e0759-caa1-4cfa-bc3f-402593f1eee3@redhat.com/
>
> Signed-off-by: wang lian <lianux.mm@gmail.com>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> ---
> tools/testing/selftests/mm/cow.c | 30 +++++++++----------
> tools/testing/selftests/mm/guard-regions.c | 7 -----
> tools/testing/selftests/mm/hugetlb-madvise.c | 5 +---
> tools/testing/selftests/mm/migration.c | 13 ++++----
> tools/testing/selftests/mm/pagemap_ioctl.c | 4 +--
> .../selftests/mm/split_huge_page_test.c | 4 +--
> tools/testing/selftests/mm/vm_util.h | 7 +++++
> 7 files changed, 31 insertions(+), 39 deletions(-)
>
<snip>
> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
> index f0d9c035641d..05de1fc0005b 100644
> --- a/tools/testing/selftests/mm/split_huge_page_test.c
> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
> @@ -399,7 +399,6 @@ int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size, int *fd,
> char **addr)
> {
> size_t i;
> - int dummy = 0;
> unsigned char buf[1024];
>
> srand(time(NULL));
> @@ -441,8 +440,7 @@ 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++)
> - dummy += *(*addr + i);
> - asm volatile("" : "+r" (dummy));
> + FORCE_READ((*addr + i));
I encountered a segfault when running the test on x86_64.
i is 4194297 and fd_size is 4194304.
It seems that FORCE_READ() is reading (*addr + i) in 8 byte size
and i is only 7 bytes away from the end of the memory address.
This led to segfault.
(*(volatile char*)(*addr + i)); works fine.
Both gcc-12 and gcc-14 have the issue.
>
> 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 2b154c287591..c20298ae98ea 100644
> --- a/tools/testing/selftests/mm/vm_util.h
> +++ b/tools/testing/selftests/mm/vm_util.h
> @@ -18,6 +18,13 @@
> #define PM_SWAP BIT_ULL(62)
> #define PM_PRESENT BIT_ULL(63)
>
> +/*
> + * Ignore the checkpatch warning, we must read from x but don't want to do
> + * 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)
> +
Also, look at FORCE_READ again, it converts x to a pointer to x and
deferences x as a point. It does not seem right to me.
Best Regards,
Yan, Zi
On Tue, 05 Aug 2025 10:26:17 -0400
Zi Yan <ziy@nvidia.com> wrote:
> On 17 Jul 2025, at 9:18, wang lian wrote:
>
> > Several mm selftests use the `asm volatile("" : "+r" (variable));`
> > construct to force a read of a variable, preventing the compiler from
> > optimizing away the memory access. This idiom is cryptic and duplicated
> > across multiple test files.
> >
> > Following a suggestion from David[1], this patch refactors this
> > common pattern into a FORCE_READ() macro
> >
> > [1] https://lore.kernel.org/lkml/4a3e0759-caa1-4cfa-bc3f-402593f1eee3@redhat.com/
> >
> > Signed-off-by: wang lian <lianux.mm@gmail.com>
> > Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> > ---
> > tools/testing/selftests/mm/cow.c | 30 +++++++++----------
> > tools/testing/selftests/mm/guard-regions.c | 7 -----
> > tools/testing/selftests/mm/hugetlb-madvise.c | 5 +---
> > tools/testing/selftests/mm/migration.c | 13 ++++----
> > tools/testing/selftests/mm/pagemap_ioctl.c | 4 +--
> > .../selftests/mm/split_huge_page_test.c | 4 +--
> > tools/testing/selftests/mm/vm_util.h | 7 +++++
> > 7 files changed, 31 insertions(+), 39 deletions(-)
> >
>
> <snip>
>
> > diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
> > index f0d9c035641d..05de1fc0005b 100644
> > --- a/tools/testing/selftests/mm/split_huge_page_test.c
> > +++ b/tools/testing/selftests/mm/split_huge_page_test.c
> > @@ -399,7 +399,6 @@ int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size, int *fd,
> > char **addr)
> > {
> > size_t i;
> > - int dummy = 0;
> > unsigned char buf[1024];
> >
> > srand(time(NULL));
> > @@ -441,8 +440,7 @@ 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++)
> > - dummy += *(*addr + i);
> > - asm volatile("" : "+r" (dummy));
> > + FORCE_READ((*addr + i));
>
> I encountered a segfault when running the test on x86_64.
> i is 4194297 and fd_size is 4194304.
> It seems that FORCE_READ() is reading (*addr + i) in 8 byte size
> and i is only 7 bytes away from the end of the memory address.
> This led to segfault.
>
> (*(volatile char*)(*addr + i)); works fine.
>
> Both gcc-12 and gcc-14 have the issue.
The definition of FORCE_READ in 6.16 is:
#define FORCE_READ(x) (*(volatile typeof(x) *)x)
this is clearly bogus.
'x' is a pointer - follow it through.
Possibly:
#define FORCE_READ(x) (*(volatile typeof(*(x)) *)(x))
is better,
But why not use READ_ONCE(*addr[i]) ?
David
>
> >
> > 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 2b154c287591..c20298ae98ea 100644
> > --- a/tools/testing/selftests/mm/vm_util.h
> > +++ b/tools/testing/selftests/mm/vm_util.h
> > @@ -18,6 +18,13 @@
> > #define PM_SWAP BIT_ULL(62)
> > #define PM_PRESENT BIT_ULL(63)
> >
> > +/*
> > + * Ignore the checkpatch warning, we must read from x but don't want to do
> > + * 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)
> > +
>
> Also, look at FORCE_READ again, it converts x to a pointer to x and
> deferences x as a point. It does not seem right to me.
>
> Best Regards,
> Yan, Zi
>
On 7 Aug 2025, at 8:16, David Laight wrote:
> On Tue, 05 Aug 2025 10:26:17 -0400
> Zi Yan <ziy@nvidia.com> wrote:
>
>> On 17 Jul 2025, at 9:18, wang lian wrote:
>>
>>> Several mm selftests use the `asm volatile("" : "+r" (variable));`
>>> construct to force a read of a variable, preventing the compiler from
>>> optimizing away the memory access. This idiom is cryptic and duplicated
>>> across multiple test files.
>>>
>>> Following a suggestion from David[1], this patch refactors this
>>> common pattern into a FORCE_READ() macro
>>>
>>> [1] https://lore.kernel.org/lkml/4a3e0759-caa1-4cfa-bc3f-402593f1eee3@redhat.com/
>>>
>>> Signed-off-by: wang lian <lianux.mm@gmail.com>
>>> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
>>> ---
>>> tools/testing/selftests/mm/cow.c | 30 +++++++++----------
>>> tools/testing/selftests/mm/guard-regions.c | 7 -----
>>> tools/testing/selftests/mm/hugetlb-madvise.c | 5 +---
>>> tools/testing/selftests/mm/migration.c | 13 ++++----
>>> tools/testing/selftests/mm/pagemap_ioctl.c | 4 +--
>>> .../selftests/mm/split_huge_page_test.c | 4 +--
>>> tools/testing/selftests/mm/vm_util.h | 7 +++++
>>> 7 files changed, 31 insertions(+), 39 deletions(-)
>>>
>>
>> <snip>
>>
>>> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
>>> index f0d9c035641d..05de1fc0005b 100644
>>> --- a/tools/testing/selftests/mm/split_huge_page_test.c
>>> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
>>> @@ -399,7 +399,6 @@ int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size, int *fd,
>>> char **addr)
>>> {
>>> size_t i;
>>> - int dummy = 0;
>>> unsigned char buf[1024];
>>>
>>> srand(time(NULL));
>>> @@ -441,8 +440,7 @@ 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++)
>>> - dummy += *(*addr + i);
>>> - asm volatile("" : "+r" (dummy));
>>> + FORCE_READ((*addr + i));
>>
>> I encountered a segfault when running the test on x86_64.
>> i is 4194297 and fd_size is 4194304.
>> It seems that FORCE_READ() is reading (*addr + i) in 8 byte size
>> and i is only 7 bytes away from the end of the memory address.
>> This led to segfault.
>>
>> (*(volatile char*)(*addr + i)); works fine.
>>
>> Both gcc-12 and gcc-14 have the issue.
>
> The definition of FORCE_READ in 6.16 is:
> #define FORCE_READ(x) (*(volatile typeof(x) *)x)
> this is clearly bogus.
> 'x' is a pointer - follow it through.
> Possibly:
> #define FORCE_READ(x) (*(volatile typeof(*(x)) *)(x))
> is better,
> But why not use READ_ONCE(*addr[i]) ?
Yeah, that is my fix to this:
https://lore.kernel.org/linux-mm/20250805175140.241656-1-ziy@nvidia.com/
>
>>
>>>
>>> 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 2b154c287591..c20298ae98ea 100644
>>> --- a/tools/testing/selftests/mm/vm_util.h
>>> +++ b/tools/testing/selftests/mm/vm_util.h
>>> @@ -18,6 +18,13 @@
>>> #define PM_SWAP BIT_ULL(62)
>>> #define PM_PRESENT BIT_ULL(63)
>>>
>>> +/*
>>> + * Ignore the checkpatch warning, we must read from x but don't want to do
>>> + * 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)
>>> +
>>
>> Also, look at FORCE_READ again, it converts x to a pointer to x and
>> deferences x as a point. It does not seem right to me.
>>
>> Best Regards,
>> Yan, Zi
>>
--
Best Regards,
Yan, Zi
On 17 Jul 2025, at 9:18, wang lian wrote:
> Several mm selftests use the `asm volatile("" : "+r" (variable));`
> construct to force a read of a variable, preventing the compiler from
> optimizing away the memory access. This idiom is cryptic and duplicated
> across multiple test files.
>
> Following a suggestion from David[1], this patch refactors this
> common pattern into a FORCE_READ() macro
>
> [1] https://lore.kernel.org/lkml/4a3e0759-caa1-4cfa-bc3f-402593f1eee3@redhat.com/
>
> Signed-off-by: wang lian <lianux.mm@gmail.com>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> ---
> tools/testing/selftests/mm/cow.c | 30 +++++++++----------
> tools/testing/selftests/mm/guard-regions.c | 7 -----
> tools/testing/selftests/mm/hugetlb-madvise.c | 5 +---
> tools/testing/selftests/mm/migration.c | 13 ++++----
> tools/testing/selftests/mm/pagemap_ioctl.c | 4 +--
> .../selftests/mm/split_huge_page_test.c | 4 +--
> tools/testing/selftests/mm/vm_util.h | 7 +++++
> 7 files changed, 31 insertions(+), 39 deletions(-)
Reviewed-by: Zi Yan <ziy@nvidia.com>
Best Regards,
Yan, Zi
On Thu, Jul 17, 2025 at 09:18:56PM +0800, wang lian wrote:
>Several mm selftests use the `asm volatile("" : "+r" (variable));`
>construct to force a read of a variable, preventing the compiler from
>optimizing away the memory access. This idiom is cryptic and duplicated
>across multiple test files.
>
>Following a suggestion from David[1], this patch refactors this
>common pattern into a FORCE_READ() macro
>
>[1] https://lore.kernel.org/lkml/4a3e0759-caa1-4cfa-bc3f-402593f1eee3@redhat.com/
>
>Signed-off-by: wang lian <lianux.mm@gmail.com>
>Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
--
Wei Yang
Help you, Help me
> On Thu, Jul 17, 2025 at 09:18:56PM +0800, wang lian wrote:
> >Several mm selftests use the `asm volatile("" : "+r" (variable));`
> >construct to force a read of a variable, preventing the compiler from
> >optimizing away the memory access. This idiom is cryptic and duplicated
> >across multiple test files.
> >
> >Following a suggestion from David[1], this patch refactors this
> >common pattern into a FORCE_READ() macro
> >
> >[1] https://lore.kernel.org/lkml/4a3e0759-caa1-4cfa-bc3f-402593f1eee3@redhat.com/
> >
> >Signed-off-by: wang lian <lianux.mm@gmail.com>
> >Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Thanks!
> --
> Wei Yang
> Help you, Help me
Best regards,
Wang Lian
On 17.07.25 15:18, wang lian wrote:
> Several mm selftests use the `asm volatile("" : "+r" (variable));`
> construct to force a read of a variable, preventing the compiler from
> optimizing away the memory access. This idiom is cryptic and duplicated
> across multiple test files.
>
> Following a suggestion from David[1], this patch refactors this
> common pattern into a FORCE_READ() macro
>
> [1] https://lore.kernel.org/lkml/4a3e0759-caa1-4cfa-bc3f-402593f1eee3@redhat.com/
>
> Signed-off-by: wang lian <lianux.mm@gmail.com>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> ---
Acked-by: David Hildenbrand <david@redhat.com>
--
Cheers,
David / dhildenb
> On 17.07.25 15:18, wang lian wrote:
> > Several mm selftests use the `asm volatile("" : "+r" (variable));`
> > construct to force a read of a variable, preventing the compiler from
> > optimizing away the memory access. This idiom is cryptic and duplicated
> > across multiple test files.
> >
> > Following a suggestion from David[1], this patch refactors this
> > common pattern into a FORCE_READ() macro
> >
> > [1] https://lore.kernel.org/lkml/4a3e0759-caa1-4cfa-bc3f-402593f1eee3@redhat.com/
> >
> > Signed-off-by: wang lian <lianux.mm@gmail.com>
> > Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> > ---
Hi David,
Thank you for the review and the Acked-by tag. I appreciate it.
> Acked-by: David Hildenbrand <david@redhat.com>
> --
> Cheers,
> David / dhildenb
Best regards,
Wang Lian
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