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Message-ID: <84df3b17-6f3d-4e9b-94e0-88ba186207e2@arm.com>
Date: Thu, 2 Nov 2023 12:29:54 +0000
From: Ryan Roberts <ryan.roberts@....com>
To: Breno Leitao <leitao@...ian.org>, mike.kravetz@...cle.com,
muchun.song@...ux.dev, akpm@...ux-foundation.org,
Shuah Khan <shuah@...nel.org>
Cc: linux-mm@...ck.org, riel@...riel.com,
open list <linux-kernel@...r.kernel.org>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] selftests/mm: Add a new test for madv and hugetlb
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) "$@"
>> [FAIL]
>>
>> This selftest goes together with the fix of the bug[1] itself.
>>
>> [1] https://lore.kernel.org/all/20231001005659.2185316-1-riel@surriel.com/#r
>>
>> Signed-off-by: Breno Leitao <leitao@...ian.org>
>> ---
>> tools/testing/selftests/mm/Makefile | 1 +
>> .../selftests/mm/hugetlb_fault_after_madv.c | 73 +++++++++++++++++++
>> tools/testing/selftests/mm/run_vmtests.sh | 4 +
>> 3 files changed, 78 insertions(+)
>> create mode 100644 tools/testing/selftests/mm/hugetlb_fault_after_madv.c
>>
>> diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
>> index 6a9fc5693145..e71ec9910c62 100644
>> --- a/tools/testing/selftests/mm/Makefile
>> +++ b/tools/testing/selftests/mm/Makefile
>> @@ -68,6 +68,7 @@ TEST_GEN_FILES += split_huge_page_test
>> TEST_GEN_FILES += ksm_tests
>> TEST_GEN_FILES += ksm_functional_tests
>> TEST_GEN_FILES += mdwe_test
>> +TEST_GEN_FILES += hugetlb_fault_after_madv
>>
>> ifneq ($(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.
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"
>
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