[PATCH RFC 2/2] selftests/x86/fsgsbase: Default to trying to run the test repeatedly

[Mark Brown <broonie@kernel.org>]

In automated testing it has been found that on many systems the fsgsbase
test fails intermittently.  This was reported and discussed a while
back:

    https://lore.kernel.org/lkml/20180126153631.ha7yc33fj5uhitjo@xps/

with the analysis concluding that this is a hardware issue affecting a
subset of systems but no fix has been merged as yet.  As well as the
actual problem found by testing the intermittent test failure is causing
issues for the people doing the automated testing due to the noise.

In order to make the testing stable modify the test program to iterate
through the test repeatedly, choosing 5000 iterations based on prior
reports and local testing.  This unfortunately greatly increases the
execution time for the selftests when things succeed which isn't great,
in my local tests on a range of systems it pushes the execution time up
to approximately a minute when no failures are encountered.

Reported-by: Dan Rue <dan.rue@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
 tools/testing/selftests/x86/fsgsbase.c | 27 +++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c
index 6cda6daa1f8c..83410749ff1f 100644
--- a/tools/testing/selftests/x86/fsgsbase.c
+++ b/tools/testing/selftests/x86/fsgsbase.c
@@ -379,7 +379,7 @@ static void test_unexpected_base(void)
 	}
 }
 
-int main()
+int test()
 {
 	pthread_t thread;
 
@@ -437,3 +437,28 @@ int main()
 
 	return nerrs == 0 ? 0 : 1;
 }
+
+int main()
+{
+	int tries = 5000;
+	int i;
+
+	if (tries > 1)
+		quiet = true;
+
+	for (i = 0; i < tries; i++) {
+		if (test() != 0)
+			break;
+	}
+
+	if (quiet) {
+		if (nerrs) {
+			printf("[FAIL] %d errors detected in %d tries\n",
+				nerrs, i + 1);
+		} else {
+			printf("[PASS] %d runs succeeded\n", i);
+		}
+	}
+
+	return nerrs == 0 ? 0 : 1;
+}
-- 
2.19.1