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