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