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authorAndrea Arcangeli <aarcange@redhat.com>2015-09-22 14:59:00 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2015-09-22 15:09:53 -0700
commit1f5fee2cf232f9fac05b65f21107d2cf3c32092c (patch)
tree128e8442c6a20e983b9c7939b2e91c55e03f6df5 /tools
parent56ed8f169e225dce1f9e40f6eee2e2dabe7d06fc (diff)
downloadlinux-1f5fee2cf232f9fac05b65f21107d2cf3c32092c.tar.bz2
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>
Diffstat (limited to 'tools')
-rw-r--r--tools/testing/selftests/vm/userfaultfd.c12
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;