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) "$@" [FAIL]
This selftest goes together with the fix of the bug[1] itself.
[1] https://lore.kernel.org/all/20231001005659.2185316-1-riel@surriel.com/#r
Signed-off-by: Breno Leitao leitao@debian.org
tools/testing/selftests/mm/Makefile | 1 + .../selftests/mm/hugetlb_fault_after_madv.c | 73 +++++++++++++++++++ tools/testing/selftests/mm/run_vmtests.sh | 4 + 3 files changed, 78 insertions(+) create mode 100644 tools/testing/selftests/mm/hugetlb_fault_after_madv.c
diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile index 6a9fc5693145..e71ec9910c62 100644 --- a/tools/testing/selftests/mm/Makefile +++ b/tools/testing/selftests/mm/Makefile @@ -68,6 +68,7 @@ TEST_GEN_FILES += split_huge_page_test TEST_GEN_FILES += ksm_tests TEST_GEN_FILES += ksm_functional_tests TEST_GEN_FILES += mdwe_test +TEST_GEN_FILES += hugetlb_fault_after_madv ifneq ($(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.