The patch titled
Subject: userfaultfd: selftest: avoid my_bcmp false positives with powerpc
has been added to the -mm tree. Its filename is
userfaultfd-selftest-avoid-my_bcmp-false-positives-with-powerpc.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/userfaultfd-selftest-avoid-my_bcmp-false-positives-with-powerpc.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/userfaultfd-selftest-avoid-my_bcmp-false-positives-with-powerpc.patch
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------------------------------------------------------
From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Subject: 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@xxxxxxxxxx>
Tested-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Dr. David Alan Gilbert <dgilbert@xxxxxxxxxx>
Cc: Shuah Khan <shuahkh@xxxxxxxxxxxxxxx>
Cc: Thierry Reding <treding@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
tools/testing/selftests/vm/userfaultfd.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff -puN tools/testing/selftests/vm/userfaultfd.c~userfaultfd-selftest-avoid-my_bcmp-false-positives-with-powerpc tools/testing/selftests/vm/userfaultfd.c
--- a/tools/testing/selftests/vm/userfaultfd.c~userfaultfd-selftest-avoid-my_bcmp-false-positives-with-powerpc
+++ a/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;
_
Patches currently in -mm which might be from aarcange@xxxxxxxxxx are
userfaultfd-revert-userfaultfd-waitqueue-add-nr-wake-parameter-to-__wake_up_locked_key.patch
userfaultfd-selftest-headers-fixup.patch
userfaultfd-selftest-avoid-my_bcmp-false-positives-with-powerpc.patch
userfaultfd-selftest-return-an-error-if-bounce_verify-fails.patch
userfaultfd-selftest-dont-error-out-if-pthread_mutex_t-isnt-identical.patch
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