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