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Date:   Tue, 16 Jun 2020 14:36:25 +0200
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Subject: [PATCH 4/4] kcsan: Add jiffies test to test suite
From:   Marco Elver <elver@google.com>
To:     elver@google.com, paulmck@kernel.org
Cc:     dvyukov@google.com, kasan-dev@googlegroups.com,
        linux-kernel@vger.kernel.org
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Sender: linux-kernel-owner@vger.kernel.org
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Add a test that KCSAN nor the compiler gets confused about accesses to
jiffies on different architectures.

Signed-off-by: Marco Elver <elver@google.com>
---
 kernel/kcsan/kcsan-test.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/kernel/kcsan/kcsan-test.c b/kernel/kcsan/kcsan-test.c
index 3af420ad6ee7..fed6fcb5768c 100644
--- a/kernel/kcsan/kcsan-test.c
+++ b/kernel/kcsan/kcsan-test.c
@@ -366,6 +366,11 @@ static noinline void test_kernel_read_struct_zero_size(void)
 	kcsan_check_read(&test_struct.val[3], 0);
 }
 
+static noinline void test_kernel_jiffies_reader(void)
+{
+	sink_value((long)jiffies);
+}
+
 static noinline void test_kernel_seqlock_reader(void)
 {
 	unsigned int seq;
@@ -817,6 +822,23 @@ static void test_assert_exclusive_access_scoped(struct kunit *test)
 	KUNIT_EXPECT_TRUE(test, match_expect_inscope);
 }
 
+/*
+ * jiffies is special (declared to be volatile) and its accesses are typically
+ * not marked; this test ensures that the compiler nor KCSAN gets confused about
+ * jiffies's declaration on different architectures.
+ */
+__no_kcsan
+static void test_jiffies_noreport(struct kunit *test)
+{
+	bool match_never = false;
+
+	begin_test_checks(test_kernel_jiffies_reader, test_kernel_jiffies_reader);
+	do {
+		match_never = report_available();
+	} while (!end_test_checks(match_never));
+	KUNIT_EXPECT_FALSE(test, match_never);
+}
+
 /* Test that racing accesses in seqlock critical sections are not reported. */
 __no_kcsan
 static void test_seqlock_noreport(struct kunit *test)
@@ -867,6 +889,7 @@ static struct kunit_case kcsan_test_cases[] = {
 	KCSAN_KUNIT_CASE(test_assert_exclusive_bits_nochange),
 	KCSAN_KUNIT_CASE(test_assert_exclusive_writer_scoped),
 	KCSAN_KUNIT_CASE(test_assert_exclusive_access_scoped),
+	KCSAN_KUNIT_CASE(test_jiffies_noreport),
 	KCSAN_KUNIT_CASE(test_seqlock_noreport),
 	{},
 };
-- 
2.27.0.290.gba653c62da-goog