Create a selftest that exercises the race between page faults and
madvise(MADV_DONTNEED) in the same huge page. Do it by running two
threads that touches the huge page and madvise(MADV_DONTNEED) at the same
time.
In case of a SIGBUS coming at pagefault, the test should fail, since we
hit the bug.
The test doesn't have a signal handler, and if it fails, it fails like
the following
----------------------------------
running ./hugetlb_fault_after_madv
----------------------------------
./run_vmtests.sh: line 186: 595563 Bus error (core dumped) "$@"
[FAIL]
This selftest goes together with the fix of the bug[1] itself.
[1] https://lore.kernel.org/all/[email protected]/#r
Signed-off-by: Breno Leitao <[email protected]>
---
tools/testing/selftests/mm/Makefile | 1 +
.../selftests/mm/hugetlb_fault_after_madv.c | 73 +++++++++++++++++++
tools/testing/selftests/mm/run_vmtests.sh | 4 +
3 files changed, 78 insertions(+)
create mode 100644 tools/testing/selftests/mm/hugetlb_fault_after_madv.c
diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index 6a9fc5693145..e71ec9910c62 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -68,6 +68,7 @@ TEST_GEN_FILES += split_huge_page_test
TEST_GEN_FILES += ksm_tests
TEST_GEN_FILES += ksm_functional_tests
TEST_GEN_FILES += mdwe_test
+TEST_GEN_FILES += hugetlb_fault_after_madv
ifneq ($(ARCH),arm64)
TEST_GEN_PROGS += soft-dirty
diff --git a/tools/testing/selftests/mm/hugetlb_fault_after_madv.c b/tools/testing/selftests/mm/hugetlb_fault_after_madv.c
new file mode 100644
index 000000000000..73b81c632366
--- /dev/null
+++ b/tools/testing/selftests/mm/hugetlb_fault_after_madv.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "vm_util.h"
+#include "../kselftest.h"
+
+#define MMAP_SIZE (1 << 21)
+#define INLOOP_ITER 100
+
+char *huge_ptr;
+
+/* Touch the memory while it is being madvised() */
+void *touch(void *unused)
+{
+ char *ptr = (char *)huge_ptr;
+
+ for (int i = 0; i < INLOOP_ITER; i++)
+ ptr[0] = '.';
+
+ return NULL;
+}
+
+void *madv(void *unused)
+{
+ usleep(rand() % 10);
+
+ for (int i = 0; i < INLOOP_ITER; i++)
+ madvise(huge_ptr, MMAP_SIZE, MADV_DONTNEED);
+
+ return NULL;
+}
+
+int main(void)
+{
+ unsigned long free_hugepages;
+ pthread_t thread1, thread2;
+ /*
+ * On kernel 6.4, we are able to reproduce the problem with ~1000
+ * interactions
+ */
+ int max = 10000;
+
+ srand(getpid());
+
+ free_hugepages = get_free_hugepages();
+ if (free_hugepages != 1) {
+ ksft_exit_skip("This test needs one and only one page to execute. Got %lu\n",
+ free_hugepages);
+ }
+
+ while (max--) {
+ huge_ptr = mmap(NULL, MMAP_SIZE, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB,
+ -1, 0);
+
+ if ((unsigned long)huge_ptr == -1)
+ ksft_exit_skip("Failed to allocated huge page\n");
+
+ pthread_create(&thread1, NULL, madv, NULL);
+ pthread_create(&thread2, NULL, touch, NULL);
+
+ pthread_join(thread1, NULL);
+ pthread_join(thread2, NULL);
+ munmap(huge_ptr, MMAP_SIZE);
+ }
+
+ return KSFT_PASS;
+}
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index 3e2bc818d566..9f53f7318a38 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -221,6 +221,10 @@ CATEGORY="hugetlb" run_test ./hugepage-mremap
CATEGORY="hugetlb" run_test ./hugepage-vmemmap
CATEGORY="hugetlb" run_test ./hugetlb-madvise
+# For this test, we need one and just one huge page
+echo 1 > /proc/sys/vm/nr_hugepages
+CATEGORY="hugetlb" run_test ./hugetlb_fault_after_madv
+
if test_selected "hugetlb"; then
echo "NOTE: These hugetlb tests provide minimal coverage. Use"
echo " https://github.com/libhugetlbfs/libhugetlbfs.git for"
--
2.34.1
On Thu, 2023-10-05 at 09:39 -0700, Breno Leitao wrote:
> Create a selftest that exercises the race between page faults and
> madvise(MADV_DONTNEED) in the same huge page. Do it by running two
> threads that touches the huge page and madvise(MADV_DONTNEED) at the
> same
> time.
>
> ----------------------------------
> ./run_vmtests.sh: line 186: 595563 Bus error (core dumped) "$@"
> [FAIL]
>
> This selftest goes together with the fix of the bug[1] itself.
>
> [1]
> https://lore.kernel.org/all/[email protected]/#r
>
> Signed-off-by: Breno Leitao <[email protected]>
Tested-and-reviewed-by: Rik van Riel <[email protected]>
--
All Rights Reversed.
Hi Breno,
On 05/10/2023 17:39, Breno Leitao wrote:
> Create a selftest that exercises the race between page faults and
> madvise(MADV_DONTNEED) in the same huge page. Do it by running two
> threads that touches the huge page and madvise(MADV_DONTNEED) at the same
> time.
>
> In case of a SIGBUS coming at pagefault, the test should fail, since we
> hit the bug.
>
> The test doesn't have a signal handler, and if it fails, it fails like
> the following
>
> ----------------------------------
> running ./hugetlb_fault_after_madv
> ----------------------------------
> ./run_vmtests.sh: line 186: 595563 Bus error (core dumped) "$@"
> [FAIL]
>
> This selftest goes together with the fix of the bug[1] itself.
>
> [1] https://lore.kernel.org/all/[email protected]/#r
>
> Signed-off-by: Breno Leitao <[email protected]>
> ---
> tools/testing/selftests/mm/Makefile | 1 +
> .../selftests/mm/hugetlb_fault_after_madv.c | 73 +++++++++++++++++++
> tools/testing/selftests/mm/run_vmtests.sh | 4 +
> 3 files changed, 78 insertions(+)
> create mode 100644 tools/testing/selftests/mm/hugetlb_fault_after_madv.c
>
> diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
> index 6a9fc5693145..e71ec9910c62 100644
> --- a/tools/testing/selftests/mm/Makefile
> +++ b/tools/testing/selftests/mm/Makefile
> @@ -68,6 +68,7 @@ TEST_GEN_FILES += split_huge_page_test
> TEST_GEN_FILES += ksm_tests
> TEST_GEN_FILES += ksm_functional_tests
> TEST_GEN_FILES += mdwe_test
> +TEST_GEN_FILES += hugetlb_fault_after_madv
>
> ifneq ($(ARCH),arm64)
> TEST_GEN_PROGS += soft-dirty
> diff --git a/tools/testing/selftests/mm/hugetlb_fault_after_madv.c b/tools/testing/selftests/mm/hugetlb_fault_after_madv.c
> new file mode 100644
> index 000000000000..73b81c632366
> --- /dev/null
> +++ b/tools/testing/selftests/mm/hugetlb_fault_after_madv.c
> @@ -0,0 +1,73 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <pthread.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <sys/mman.h>
> +#include <sys/types.h>
> +#include <unistd.h>
> +
> +#include "vm_util.h"
> +#include "../kselftest.h"
> +
> +#define MMAP_SIZE (1 << 21)
> +#define INLOOP_ITER 100
> +
> +char *huge_ptr;
> +
> +/* Touch the memory while it is being madvised() */
> +void *touch(void *unused)
> +{
> + char *ptr = (char *)huge_ptr;
> +
> + for (int i = 0; i < INLOOP_ITER; i++)
> + ptr[0] = '.';
> +
> + return NULL;
> +}
> +
> +void *madv(void *unused)
> +{
> + usleep(rand() % 10);
> +
> + for (int i = 0; i < INLOOP_ITER; i++)
> + madvise(huge_ptr, MMAP_SIZE, MADV_DONTNEED);
> +
> + return NULL;
> +}
> +
> +int main(void)
> +{
> + unsigned long free_hugepages;
> + pthread_t thread1, thread2;
> + /*
> + * On kernel 6.4, we are able to reproduce the problem with ~1000
> + * interactions
> + */
> + int max = 10000;
> +
> + srand(getpid());
> +
> + free_hugepages = get_free_hugepages();
> + if (free_hugepages != 1) {
> + ksft_exit_skip("This test needs one and only one page to execute. Got %lu\n",
> + free_hugepages);
> + }
> +
> + while (max--) {
> + huge_ptr = mmap(NULL, MMAP_SIZE, PROT_READ | PROT_WRITE,
> + MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB,
> + -1, 0);
> +
> + if ((unsigned long)huge_ptr == -1)
> + ksft_exit_skip("Failed to allocated huge page\n");
> +
> + pthread_create(&thread1, NULL, madv, NULL);
> + pthread_create(&thread2, NULL, touch, NULL);
> +
> + pthread_join(thread1, NULL);
> + pthread_join(thread2, NULL);
> + munmap(huge_ptr, MMAP_SIZE);
> + }
> +
> + return KSFT_PASS;
> +}
> diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
> index 3e2bc818d566..9f53f7318a38 100755
> --- a/tools/testing/selftests/mm/run_vmtests.sh
> +++ b/tools/testing/selftests/mm/run_vmtests.sh
> @@ -221,6 +221,10 @@ CATEGORY="hugetlb" run_test ./hugepage-mremap
> CATEGORY="hugetlb" run_test ./hugepage-vmemmap
> CATEGORY="hugetlb" run_test ./hugetlb-madvise
>
> +# For this test, we need one and just one huge page
> +echo 1 > /proc/sys/vm/nr_hugepages
I've noticed that this change breaks some of the uffd-stress tests further down
the file, because you have freed previously reserved hugepages that the test
requires to run. I notice that the patch is already in mm-stable, so perhaps its
possible to submit a patch that does a save and restore?
Although I'm not sure if that might be tricky because the previous reservation
is per-size and per-node (our CI does this on the kernel command line), and I
suspect if you want just 1 huge page in the entire system you won't be able to
get back to the previous state by just restoring this value?
These are the failing tests for reference:
# ------------------------------------
# running ./uffd-stress hugetlb 128 32
# ------------------------------------
# nr_pages: 64, nr_pages_per_cpu: 8
# ERROR: context init failed (errno=12, @uffd-stress.c:254)
# [FAIL]
# --------------------------------------------
# running ./uffd-stress hugetlb-private 128 32
# --------------------------------------------
# nr_pages: 64, nr_pages_per_cpu: 8
# ERROR: context init failed (errno=12, @uffd-stress.c:254)
# [FAIL]
Thanks,
Ryan
> +CATEGORY="hugetlb" run_test ./hugetlb_fault_after_madv
> +
> if test_selected "hugetlb"; then
> echo "NOTE: These hugetlb tests provide minimal coverage. Use"
> echo " https://github.com/libhugetlbfs/libhugetlbfs.git for"
On 02/11/2023 12:24, Ryan Roberts wrote:
> Hi Breno,
>
>
> On 05/10/2023 17:39, Breno Leitao wrote:
>> Create a selftest that exercises the race between page faults and
>> madvise(MADV_DONTNEED) in the same huge page. Do it by running two
>> threads that touches the huge page and madvise(MADV_DONTNEED) at the same
>> time.
>>
>> In case of a SIGBUS coming at pagefault, the test should fail, since we
>> hit the bug.
>>
>> The test doesn't have a signal handler, and if it fails, it fails like
>> the following
>>
>> ----------------------------------
>> running ./hugetlb_fault_after_madv
>> ----------------------------------
>> ./run_vmtests.sh: line 186: 595563 Bus error (core dumped) "$@"
>> [FAIL]
>>
>> This selftest goes together with the fix of the bug[1] itself.
>>
>> [1] https://lore.kernel.org/all/[email protected]/#r
>>
>> Signed-off-by: Breno Leitao <[email protected]>
>> ---
>> tools/testing/selftests/mm/Makefile | 1 +
>> .../selftests/mm/hugetlb_fault_after_madv.c | 73 +++++++++++++++++++
>> tools/testing/selftests/mm/run_vmtests.sh | 4 +
>> 3 files changed, 78 insertions(+)
>> create mode 100644 tools/testing/selftests/mm/hugetlb_fault_after_madv.c
>>
>> diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
>> index 6a9fc5693145..e71ec9910c62 100644
>> --- a/tools/testing/selftests/mm/Makefile
>> +++ b/tools/testing/selftests/mm/Makefile
>> @@ -68,6 +68,7 @@ TEST_GEN_FILES += split_huge_page_test
>> TEST_GEN_FILES += ksm_tests
>> TEST_GEN_FILES += ksm_functional_tests
>> TEST_GEN_FILES += mdwe_test
>> +TEST_GEN_FILES += hugetlb_fault_after_madv
>>
>> ifneq ($(ARCH),arm64)
>> TEST_GEN_PROGS += soft-dirty
>> diff --git a/tools/testing/selftests/mm/hugetlb_fault_after_madv.c b/tools/testing/selftests/mm/hugetlb_fault_after_madv.c
>> new file mode 100644
>> index 000000000000..73b81c632366
>> --- /dev/null
>> +++ b/tools/testing/selftests/mm/hugetlb_fault_after_madv.c
>> @@ -0,0 +1,73 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +#include <pthread.h>
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +#include <sys/mman.h>
>> +#include <sys/types.h>
>> +#include <unistd.h>
>> +
>> +#include "vm_util.h"
>> +#include "../kselftest.h"
>> +
>> +#define MMAP_SIZE (1 << 21)
>> +#define INLOOP_ITER 100
>> +
>> +char *huge_ptr;
>> +
>> +/* Touch the memory while it is being madvised() */
>> +void *touch(void *unused)
>> +{
>> + char *ptr = (char *)huge_ptr;
>> +
>> + for (int i = 0; i < INLOOP_ITER; i++)
>> + ptr[0] = '.';
>> +
>> + return NULL;
>> +}
>> +
>> +void *madv(void *unused)
>> +{
>> + usleep(rand() % 10);
>> +
>> + for (int i = 0; i < INLOOP_ITER; i++)
>> + madvise(huge_ptr, MMAP_SIZE, MADV_DONTNEED);
>> +
>> + return NULL;
>> +}
>> +
>> +int main(void)
>> +{
>> + unsigned long free_hugepages;
>> + pthread_t thread1, thread2;
>> + /*
>> + * On kernel 6.4, we are able to reproduce the problem with ~1000
>> + * interactions
>> + */
>> + int max = 10000;
>> +
>> + srand(getpid());
>> +
>> + free_hugepages = get_free_hugepages();
>> + if (free_hugepages != 1) {
>> + ksft_exit_skip("This test needs one and only one page to execute. Got %lu\n",
>> + free_hugepages);
>> + }
>> +
>> + while (max--) {
>> + huge_ptr = mmap(NULL, MMAP_SIZE, PROT_READ | PROT_WRITE,
>> + MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB,
>> + -1, 0);
>> +
>> + if ((unsigned long)huge_ptr == -1)
>> + ksft_exit_skip("Failed to allocated huge page\n");
>> +
>> + pthread_create(&thread1, NULL, madv, NULL);
>> + pthread_create(&thread2, NULL, touch, NULL);
>> +
>> + pthread_join(thread1, NULL);
>> + pthread_join(thread2, NULL);
>> + munmap(huge_ptr, MMAP_SIZE);
>> + }
>> +
>> + return KSFT_PASS;
>> +}
>> diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
>> index 3e2bc818d566..9f53f7318a38 100755
>> --- a/tools/testing/selftests/mm/run_vmtests.sh
>> +++ b/tools/testing/selftests/mm/run_vmtests.sh
>> @@ -221,6 +221,10 @@ CATEGORY="hugetlb" run_test ./hugepage-mremap
>> CATEGORY="hugetlb" run_test ./hugepage-vmemmap
>> CATEGORY="hugetlb" run_test ./hugetlb-madvise
>>
>> +# For this test, we need one and just one huge page
>> +echo 1 > /proc/sys/vm/nr_hugepages
>
> I've noticed that this change breaks some of the uffd-stress tests further down
> the file, because you have freed previously reserved hugepages that the test
> requires to run. I notice that the patch is already in mm-stable, so perhaps its
> possible to submit a patch that does a save and restore?
>
> Although I'm not sure if that might be tricky because the previous reservation
> is per-size and per-node (our CI does this on the kernel command line), and I
> suspect if you want just 1 huge page in the entire system you won't be able to
> get back to the previous state by just restoring this value?
Actually on closer inspection, I don't think this will be a problem; simply
saving and restoring the value around the test will be sufficient.
I also notice that the binary for the new test is not added to the .gitignore,
which is a minor annoyance.
Thanks,
Ryan
>
> These are the failing tests for reference:
>
> # ------------------------------------
> # running ./uffd-stress hugetlb 128 32
> # ------------------------------------
> # nr_pages: 64, nr_pages_per_cpu: 8
> # ERROR: context init failed (errno=12, @uffd-stress.c:254)
> # [FAIL]
> # --------------------------------------------
> # running ./uffd-stress hugetlb-private 128 32
> # --------------------------------------------
> # nr_pages: 64, nr_pages_per_cpu: 8
> # ERROR: context init failed (errno=12, @uffd-stress.c:254)
> # [FAIL]
>
> Thanks,
> Ryan
>
>
>
>> +CATEGORY="hugetlb" run_test ./hugetlb_fault_after_madv
>> +
>> if test_selected "hugetlb"; then
>> echo "NOTE: These hugetlb tests provide minimal coverage. Use"
>> echo " https://github.com/libhugetlbfs/libhugetlbfs.git for"
>
Hello Ryan,
On Thu, Nov 02, 2023 at 12:29:54PM +0000, Ryan Roberts wrote:
> On 02/11/2023 12:24, Ryan Roberts wrote:
> > On 05/10/2023 17:39, Breno Leitao wrote:
> >> Create a selftest that exercises the race between page faults and
> >> madvise(MADV_DONTNEED) in the same huge page. Do it by running two
> >> threads that touches the huge page and madvise(MADV_DONTNEED) at the same
> >> time.
> >>
> >> In case of a SIGBUS coming at pagefault, the test should fail, since we
> >> hit the bug.
> >>
> >> The test doesn't have a signal handler, and if it fails, it fails like
> >> the following
> >>
> >> ----------------------------------
> >> running ./hugetlb_fault_after_madv
> >> ----------------------------------
> >> ./run_vmtests.sh: line 186: 595563 Bus error (core dumped) "$@"
> >> [FAIL]
> >>
> >> This selftest goes together with the fix of the bug[1] itself.
> >>
> >> [1] https://lore.kernel.org/all/[email protected]/#r
> >>
> >> Signed-off-by: Breno Leitao <[email protected]>
> >> ---
> >> tools/testing/selftests/mm/Makefile | 1 +
> >> .../selftests/mm/hugetlb_fault_after_madv.c | 73 +++++++++++++++++++
> >> tools/testing/selftests/mm/run_vmtests.sh | 4 +
> >> 3 files changed, 78 insertions(+)
> >> create mode 100644 tools/testing/selftests/mm/hugetlb_fault_after_madv.c
> >>
> >> diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
> >> index 6a9fc5693145..e71ec9910c62 100644
> >> --- a/tools/testing/selftests/mm/Makefile
> >> +++ b/tools/testing/selftests/mm/Makefile
> >> @@ -68,6 +68,7 @@ TEST_GEN_FILES += split_huge_page_test
> >> TEST_GEN_FILES += ksm_tests
> >> TEST_GEN_FILES += ksm_functional_tests
> >> TEST_GEN_FILES += mdwe_test
> >> +TEST_GEN_FILES += hugetlb_fault_after_madv
> >>
> >> ifneq ($(ARCH),arm64)
> >> TEST_GEN_PROGS += soft-dirty
> >> diff --git a/tools/testing/selftests/mm/hugetlb_fault_after_madv.c b/tools/testing/selftests/mm/hugetlb_fault_after_madv.c
> >> new file mode 100644
> >> index 000000000000..73b81c632366
> >> --- /dev/null
> >> +++ b/tools/testing/selftests/mm/hugetlb_fault_after_madv.c
> >> @@ -0,0 +1,73 @@
> >> +// SPDX-License-Identifier: GPL-2.0
> >> +#include <pthread.h>
> >> +#include <stdio.h>
> >> +#include <stdlib.h>
> >> +#include <sys/mman.h>
> >> +#include <sys/types.h>
> >> +#include <unistd.h>
> >> +
> >> +#include "vm_util.h"
> >> +#include "../kselftest.h"
> >> +
> >> +#define MMAP_SIZE (1 << 21)
> >> +#define INLOOP_ITER 100
> >> +
> >> +char *huge_ptr;
> >> +
> >> +/* Touch the memory while it is being madvised() */
> >> +void *touch(void *unused)
> >> +{
> >> + char *ptr = (char *)huge_ptr;
> >> +
> >> + for (int i = 0; i < INLOOP_ITER; i++)
> >> + ptr[0] = '.';
> >> +
> >> + return NULL;
> >> +}
> >> +
> >> +void *madv(void *unused)
> >> +{
> >> + usleep(rand() % 10);
> >> +
> >> + for (int i = 0; i < INLOOP_ITER; i++)
> >> + madvise(huge_ptr, MMAP_SIZE, MADV_DONTNEED);
> >> +
> >> + return NULL;
> >> +}
> >> +
> >> +int main(void)
> >> +{
> >> + unsigned long free_hugepages;
> >> + pthread_t thread1, thread2;
> >> + /*
> >> + * On kernel 6.4, we are able to reproduce the problem with ~1000
> >> + * interactions
> >> + */
> >> + int max = 10000;
> >> +
> >> + srand(getpid());
> >> +
> >> + free_hugepages = get_free_hugepages();
> >> + if (free_hugepages != 1) {
> >> + ksft_exit_skip("This test needs one and only one page to execute. Got %lu\n",
> >> + free_hugepages);
> >> + }
> >> +
> >> + while (max--) {
> >> + huge_ptr = mmap(NULL, MMAP_SIZE, PROT_READ | PROT_WRITE,
> >> + MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB,
> >> + -1, 0);
> >> +
> >> + if ((unsigned long)huge_ptr == -1)
> >> + ksft_exit_skip("Failed to allocated huge page\n");
> >> +
> >> + pthread_create(&thread1, NULL, madv, NULL);
> >> + pthread_create(&thread2, NULL, touch, NULL);
> >> +
> >> + pthread_join(thread1, NULL);
> >> + pthread_join(thread2, NULL);
> >> + munmap(huge_ptr, MMAP_SIZE);
> >> + }
> >> +
> >> + return KSFT_PASS;
> >> +}
> >> diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
> >> index 3e2bc818d566..9f53f7318a38 100755
> >> --- a/tools/testing/selftests/mm/run_vmtests.sh
> >> +++ b/tools/testing/selftests/mm/run_vmtests.sh
> >> @@ -221,6 +221,10 @@ CATEGORY="hugetlb" run_test ./hugepage-mremap
> >> CATEGORY="hugetlb" run_test ./hugepage-vmemmap
> >> CATEGORY="hugetlb" run_test ./hugetlb-madvise
> >>
> >> +# For this test, we need one and just one huge page
> >> +echo 1 > /proc/sys/vm/nr_hugepages
> >
> > I've noticed that this change breaks some of the uffd-stress tests further down
> > the file, because you have freed previously reserved hugepages that the test
> > requires to run. I notice that the patch is already in mm-stable, so perhaps its
> > possible to submit a patch that does a save and restore?
> >
> > Although I'm not sure if that might be tricky because the previous reservation
> > is per-size and per-node (our CI does this on the kernel command line), and I
> > suspect if you want just 1 huge page in the entire system you won't be able to
> > get back to the previous state by just restoring this value?
>
> Actually on closer inspection, I don't think this will be a problem; simply
> saving and restoring the value around the test will be sufficient.
Thanks for checking it, I will prepare a patch that will restore the number
of huge pages allocated after the test.
> I also notice that the binary for the new test is not added to the .gitignore,
> which is a minor annoyance.
I will add the file to .gitignore also.
Thanks for the heads-up.
On 03/11/2023 13:59, Breno Leitao wrote:
> Hello Ryan,
>
> On Thu, Nov 02, 2023 at 12:29:54PM +0000, Ryan Roberts wrote:
>> On 02/11/2023 12:24, Ryan Roberts wrote:
>>> On 05/10/2023 17:39, Breno Leitao wrote:
>>>> Create a selftest that exercises the race between page faults and
>>>> madvise(MADV_DONTNEED) in the same huge page. Do it by running two
>>>> threads that touches the huge page and madvise(MADV_DONTNEED) at the same
>>>> time.
>>>>
>>>> In case of a SIGBUS coming at pagefault, the test should fail, since we
>>>> hit the bug.
>>>>
>>>> The test doesn't have a signal handler, and if it fails, it fails like
>>>> the following
>>>>
>>>> ----------------------------------
>>>> running ./hugetlb_fault_after_madv
>>>> ----------------------------------
>>>> ./run_vmtests.sh: line 186: 595563 Bus error (core dumped) "$@"
>>>> [FAIL]
>>>>
>>>> This selftest goes together with the fix of the bug[1] itself.
>>>>
>>>> [1] https://lore.kernel.org/all/[email protected]/#r
>>>>
>>>> Signed-off-by: Breno Leitao <[email protected]>
>>>> ---
>>>> tools/testing/selftests/mm/Makefile | 1 +
>>>> .../selftests/mm/hugetlb_fault_after_madv.c | 73 +++++++++++++++++++
>>>> tools/testing/selftests/mm/run_vmtests.sh | 4 +
>>>> 3 files changed, 78 insertions(+)
>>>> create mode 100644 tools/testing/selftests/mm/hugetlb_fault_after_madv.c
>>>>
>>>> diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
>>>> index 6a9fc5693145..e71ec9910c62 100644
>>>> --- a/tools/testing/selftests/mm/Makefile
>>>> +++ b/tools/testing/selftests/mm/Makefile
>>>> @@ -68,6 +68,7 @@ TEST_GEN_FILES += split_huge_page_test
>>>> TEST_GEN_FILES += ksm_tests
>>>> TEST_GEN_FILES += ksm_functional_tests
>>>> TEST_GEN_FILES += mdwe_test
>>>> +TEST_GEN_FILES += hugetlb_fault_after_madv
>>>>
>>>> ifneq ($(ARCH),arm64)
>>>> TEST_GEN_PROGS += soft-dirty
>>>> diff --git a/tools/testing/selftests/mm/hugetlb_fault_after_madv.c b/tools/testing/selftests/mm/hugetlb_fault_after_madv.c
>>>> new file mode 100644
>>>> index 000000000000..73b81c632366
>>>> --- /dev/null
>>>> +++ b/tools/testing/selftests/mm/hugetlb_fault_after_madv.c
>>>> @@ -0,0 +1,73 @@
>>>> +// SPDX-License-Identifier: GPL-2.0
>>>> +#include <pthread.h>
>>>> +#include <stdio.h>
>>>> +#include <stdlib.h>
>>>> +#include <sys/mman.h>
>>>> +#include <sys/types.h>
>>>> +#include <unistd.h>
>>>> +
>>>> +#include "vm_util.h"
>>>> +#include "../kselftest.h"
>>>> +
>>>> +#define MMAP_SIZE (1 << 21)
>>>> +#define INLOOP_ITER 100
>>>> +
>>>> +char *huge_ptr;
>>>> +
>>>> +/* Touch the memory while it is being madvised() */
>>>> +void *touch(void *unused)
>>>> +{
>>>> + char *ptr = (char *)huge_ptr;
>>>> +
>>>> + for (int i = 0; i < INLOOP_ITER; i++)
>>>> + ptr[0] = '.';
>>>> +
>>>> + return NULL;
>>>> +}
>>>> +
>>>> +void *madv(void *unused)
>>>> +{
>>>> + usleep(rand() % 10);
>>>> +
>>>> + for (int i = 0; i < INLOOP_ITER; i++)
>>>> + madvise(huge_ptr, MMAP_SIZE, MADV_DONTNEED);
>>>> +
>>>> + return NULL;
>>>> +}
>>>> +
>>>> +int main(void)
>>>> +{
>>>> + unsigned long free_hugepages;
>>>> + pthread_t thread1, thread2;
>>>> + /*
>>>> + * On kernel 6.4, we are able to reproduce the problem with ~1000
>>>> + * interactions
>>>> + */
>>>> + int max = 10000;
>>>> +
>>>> + srand(getpid());
>>>> +
>>>> + free_hugepages = get_free_hugepages();
>>>> + if (free_hugepages != 1) {
>>>> + ksft_exit_skip("This test needs one and only one page to execute. Got %lu\n",
>>>> + free_hugepages);
>>>> + }
>>>> +
>>>> + while (max--) {
>>>> + huge_ptr = mmap(NULL, MMAP_SIZE, PROT_READ | PROT_WRITE,
>>>> + MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB,
>>>> + -1, 0);
>>>> +
>>>> + if ((unsigned long)huge_ptr == -1)
>>>> + ksft_exit_skip("Failed to allocated huge page\n");
>>>> +
>>>> + pthread_create(&thread1, NULL, madv, NULL);
>>>> + pthread_create(&thread2, NULL, touch, NULL);
>>>> +
>>>> + pthread_join(thread1, NULL);
>>>> + pthread_join(thread2, NULL);
>>>> + munmap(huge_ptr, MMAP_SIZE);
>>>> + }
>>>> +
>>>> + return KSFT_PASS;
>>>> +}
>>>> diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
>>>> index 3e2bc818d566..9f53f7318a38 100755
>>>> --- a/tools/testing/selftests/mm/run_vmtests.sh
>>>> +++ b/tools/testing/selftests/mm/run_vmtests.sh
>>>> @@ -221,6 +221,10 @@ CATEGORY="hugetlb" run_test ./hugepage-mremap
>>>> CATEGORY="hugetlb" run_test ./hugepage-vmemmap
>>>> CATEGORY="hugetlb" run_test ./hugetlb-madvise
>>>>
>>>> +# For this test, we need one and just one huge page
>>>> +echo 1 > /proc/sys/vm/nr_hugepages
>>>
>>> I've noticed that this change breaks some of the uffd-stress tests further down
>>> the file, because you have freed previously reserved hugepages that the test
>>> requires to run. I notice that the patch is already in mm-stable, so perhaps its
>>> possible to submit a patch that does a save and restore?
>>>
>>> Although I'm not sure if that might be tricky because the previous reservation
>>> is per-size and per-node (our CI does this on the kernel command line), and I
>>> suspect if you want just 1 huge page in the entire system you won't be able to
>>> get back to the previous state by just restoring this value?
>>
>> Actually on closer inspection, I don't think this will be a problem; simply
>> saving and restoring the value around the test will be sufficient.
>
> Thanks for checking it, I will prepare a patch that will restore the number
> of huge pages allocated after the test.
>
>> I also notice that the binary for the new test is not added to the .gitignore,
>> which is a minor annoyance.
>
> I will add the file to .gitignore also.
Excellent - thanks!
>
> Thanks for the heads-up.