diff options
| author | Andrea Arcangeli | 2015-09-22 14:59:00 -0700 |
|---|---|---|
| committer | Linus Torvalds | 2015-09-22 15:09:53 -0700 |
| commit | 1f5fee2cf232f9fac05b65f21107d2cf3c32092c (patch) | |
| tree | 128e8442c6a20e983b9c7939b2e91c55e03f6df5 | |
| parent | 56ed8f169e225dce1f9e40f6eee2e2dabe7d06fc (diff) | |
userfaultfd: selftest: avoid my_bcmp false positives with powerpc
Keep a non-zero placeholder after the count, for the my_bcmp comparison
of the page against the zeropage. The lockless increment between 255 to
256 against a lockless my_bcmp could otherwise return false positives on
ppc32le.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Tested-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Thierry Reding <treding@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | tools/testing/selftests/vm/userfaultfd.c | 12 |
1 files changed, 10 insertions, 2 deletions
diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c index 0671ae1d1052..10897092823d 100644 --- a/tools/testing/selftests/vm/userfaultfd.c +++ b/tools/testing/selftests/vm/userfaultfd.c @@ -465,6 +465,14 @@ static int userfaultfd_stress(void) *area_mutex(area_src, nr) = (pthread_mutex_t) PTHREAD_MUTEX_INITIALIZER; count_verify[nr] = *area_count(area_src, nr) = 1; + /* + * In the transition between 255 to 256, powerpc will + * read out of order in my_bcmp and see both bytes as + * zero, so leave a placeholder below always non-zero + * after the count, to avoid my_bcmp to trigger false + * positives. + */ + *(area_count(area_src, nr) + 1) = 1; } pipefd = malloc(sizeof(int) * nr_cpus * 2); @@ -610,8 +618,8 @@ int main(int argc, char **argv) fprintf(stderr, "Usage: <MiB> <bounces>\n"), exit(1); nr_cpus = sysconf(_SC_NPROCESSORS_ONLN); page_size = sysconf(_SC_PAGE_SIZE); - if ((unsigned long) area_count(NULL, 0) + sizeof(unsigned long long) > - page_size) + if ((unsigned long) area_count(NULL, 0) + sizeof(unsigned long long) * 2 + > page_size) fprintf(stderr, "Impossible to run this test\n"), exit(2); nr_pages_per_cpu = atol(argv[1]) * 1024*1024 / page_size / nr_cpus; |