kcsan: Make test follow KUnit style recommendations

Per recently added KUnit style recommendations at
Documentation/dev-tools/kunit/style.rst, make the following changes to
the KCSAN test:

	1. Rename 'kcsan-test.c' to 'kcsan_test.c'.

	2. Rename suite name 'kcsan-test' to 'kcsan'.

	3. Rename CONFIG_KCSAN_TEST to CONFIG_KCSAN_KUNIT_TEST and
	   default to KUNIT_ALL_TESTS.

Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

1 files changed, 1207 insertions, 0 deletions

diff --git a/kernel/kcsan/kcsan_test.c b/kernel/kcsan/kcsan_test.c
new file mode 100644
index 000000000000..f16f632eb416
--- /dev/null
+++ b/kernel/kcsan/kcsan_test.c
@@ -0,0 +1,1207 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KCSAN test with various race scenarious to test runtime behaviour. Since the
+ * interface with which KCSAN's reports are obtained is via the console, this is
+ * the output we should verify. For each test case checks the presence (or
+ * absence) of generated reports. Relies on 'console' tracepoint to capture
+ * reports as they appear in the kernel log.
+ *
+ * Makes use of KUnit for test organization, and the Torture framework for test
+ * thread control.
+ *
+ * Copyright (C) 2020, Google LLC.
+ * Author: Marco Elver <elver@google.com>
+ */
+
+#include <kunit/test.h>
+#include <linux/jiffies.h>
+#include <linux/kcsan-checks.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/seqlock.h>
+#include <linux/spinlock.h>
+#include <linux/string.h>
+#include <linux/timer.h>
+#include <linux/torture.h>
+#include <linux/tracepoint.h>
+#include <linux/types.h>
+#include <trace/events/printk.h>
+
+#ifdef CONFIG_CC_HAS_TSAN_COMPOUND_READ_BEFORE_WRITE
+#define __KCSAN_ACCESS_RW(alt) (KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE)
+#else
+#define __KCSAN_ACCESS_RW(alt) (alt)
+#endif
+
+/* Points to current test-case memory access "kernels". */
+static void (*access_kernels[2])(void);
+
+static struct task_struct **threads; /* Lists of threads. */
+static unsigned long end_time;       /* End time of test. */
+
+/* Report as observed from console. */
+static struct {
+	spinlock_t lock;
+	int nlines;
+	char lines[3][512];
+} observed = {
+	.lock = __SPIN_LOCK_UNLOCKED(observed.lock),
+};
+
+/* Setup test checking loop. */
+static __no_kcsan inline void
+begin_test_checks(void (*func1)(void), void (*func2)(void))
+{
+	kcsan_disable_current();
+
+	/*
+	 * Require at least as long as KCSAN_REPORT_ONCE_IN_MS, to ensure at
+	 * least one race is reported.
+	 */
+	end_time = jiffies + msecs_to_jiffies(CONFIG_KCSAN_REPORT_ONCE_IN_MS + 500);
+
+	/* Signal start; release potential initialization of shared data. */
+	smp_store_release(&access_kernels[0], func1);
+	smp_store_release(&access_kernels[1], func2);
+}
+
+/* End test checking loop. */
+static __no_kcsan inline bool
+end_test_checks(bool stop)
+{
+	if (!stop && time_before(jiffies, end_time)) {
+		/* Continue checking */
+		might_sleep();
+		return false;
+	}
+
+	kcsan_enable_current();
+	return true;
+}
+
+/*
+ * Probe for console output: checks if a race was reported, and obtains observed
+ * lines of interest.
+ */
+__no_kcsan
+static void probe_console(void *ignore, const char *buf, size_t len)
+{
+	unsigned long flags;
+	int nlines;
+
+	/*
+	 * Note that KCSAN reports under a global lock, so we do not risk the
+	 * possibility of having multiple reports interleaved. If that were the
+	 * case, we'd expect tests to fail.
+	 */
+
+	spin_lock_irqsave(&observed.lock, flags);
+	nlines = observed.nlines;
+
+	if (strnstr(buf, "BUG: KCSAN: ", len) && strnstr(buf, "test_", len)) {
+		/*
+		 * KCSAN report and related to the test.
+		 *
+		 * The provided @buf is not NUL-terminated; copy no more than
+		 * @len bytes and let strscpy() add the missing NUL-terminator.
+		 */
+		strscpy(observed.lines[0], buf, min(len + 1, sizeof(observed.lines[0])));
+		nlines = 1;
+	} else if ((nlines == 1 || nlines == 2) && strnstr(buf, "bytes by", len)) {
+		strscpy(observed.lines[nlines++], buf, min(len + 1, sizeof(observed.lines[0])));
+
+		if (strnstr(buf, "race at unknown origin", len)) {
+			if (WARN_ON(nlines != 2))
+				goto out;
+
+			/* No second line of interest. */
+			strcpy(observed.lines[nlines++], "<none>");
+		}
+	}
+
+out:
+	WRITE_ONCE(observed.nlines, nlines); /* Publish new nlines. */
+	spin_unlock_irqrestore(&observed.lock, flags);
+}
+
+/* Check if a report related to the test exists. */
+__no_kcsan
+static bool report_available(void)
+{
+	return READ_ONCE(observed.nlines) == ARRAY_SIZE(observed.lines);
+}
+
+/* Report information we expect in a report. */
+struct expect_report {
+	/* Access information of both accesses. */
+	struct {
+		void *fn;    /* Function pointer to expected function of top frame. */
+		void *addr;  /* Address of access; unchecked if NULL. */
+		size_t size; /* Size of access; unchecked if @addr is NULL. */
+		int type;    /* Access type, see KCSAN_ACCESS definitions. */
+	} access[2];
+};
+
+/* Check observed report matches information in @r. */
+__no_kcsan
+static bool report_matches(const struct expect_report *r)
+{
+	const bool is_assert = (r->access[0].type | r->access[1].type) & KCSAN_ACCESS_ASSERT;
+	bool ret = false;
+	unsigned long flags;
+	typeof(observed.lines) expect;
+	const char *end;
+	char *cur;
+	int i;
+
+	/* Doubled-checked locking. */
+	if (!report_available())
+		return false;
+
+	/* Generate expected report contents. */
+
+	/* Title */
+	cur = expect[0];
+	end = &expect[0][sizeof(expect[0]) - 1];
+	cur += scnprintf(cur, end - cur, "BUG: KCSAN: %s in ",
+			 is_assert ? "assert: race" : "data-race");
+	if (r->access[1].fn) {
+		char tmp[2][64];
+		int cmp;
+
+		/* Expect lexographically sorted function names in title. */
+		scnprintf(tmp[0], sizeof(tmp[0]), "%pS", r->access[0].fn);
+		scnprintf(tmp[1], sizeof(tmp[1]), "%pS", r->access[1].fn);
+		cmp = strcmp(tmp[0], tmp[1]);
+		cur += scnprintf(cur, end - cur, "%ps / %ps",
+				 cmp < 0 ? r->access[0].fn : r->access[1].fn,
+				 cmp < 0 ? r->access[1].fn : r->access[0].fn);
+	} else {
+		scnprintf(cur, end - cur, "%pS", r->access[0].fn);
+		/* The exact offset won't match, remove it. */
+		cur = strchr(expect[0], '+');
+		if (cur)
+			*cur = '\0';
+	}
+
+	/* Access 1 */
+	cur = expect[1];
+	end = &expect[1][sizeof(expect[1]) - 1];
+	if (!r->access[1].fn)
+		cur += scnprintf(cur, end - cur, "race at unknown origin, with ");
+
+	/* Access 1 & 2 */
+	for (i = 0; i < 2; ++i) {
+		const int ty = r->access[i].type;
+		const char *const access_type =
+			(ty & KCSAN_ACCESS_ASSERT) ?
+				      ((ty & KCSAN_ACCESS_WRITE) ?
+					       "assert no accesses" :
+					       "assert no writes") :
+				      ((ty & KCSAN_ACCESS_WRITE) ?
+					       ((ty & KCSAN_ACCESS_COMPOUND) ?
+							"read-write" :
+							"write") :
+					       "read");
+		const char *const access_type_aux =
+			(ty & KCSAN_ACCESS_ATOMIC) ?
+				      " (marked)" :
+				      ((ty & KCSAN_ACCESS_SCOPED) ? " (scoped)" : "");
+
+		if (i == 1) {
+			/* Access 2 */
+			cur = expect[2];
+			end = &expect[2][sizeof(expect[2]) - 1];
+
+			if (!r->access[1].fn) {
+				/* Dummy string if no second access is available. */
+				strcpy(cur, "<none>");
+				break;
+			}
+		}
+
+		cur += scnprintf(cur, end - cur, "%s%s to ", access_type,
+				 access_type_aux);
+
+		if (r->access[i].addr) /* Address is optional. */
+			cur += scnprintf(cur, end - cur, "0x%px of %zu bytes",
+					 r->access[i].addr, r->access[i].size);
+	}
+
+	spin_lock_irqsave(&observed.lock, flags);
+	if (!report_available())
+		goto out; /* A new report is being captured. */
+
+	/* Finally match expected output to what we actually observed. */
+	ret = strstr(observed.lines[0], expect[0]) &&
+	      /* Access info may appear in any order. */
+	      ((strstr(observed.lines[1], expect[1]) &&
+		strstr(observed.lines[2], expect[2])) ||
+	       (strstr(observed.lines[1], expect[2]) &&
+		strstr(observed.lines[2], expect[1])));
+out:
+	spin_unlock_irqrestore(&observed.lock, flags);
+	return ret;
+}
+
+/* ===== Test kernels ===== */
+
+static long test_sink;
+static long test_var;
+/* @test_array should be large enough to fall into multiple watchpoint slots. */
+static long test_array[3 * PAGE_SIZE / sizeof(long)];
+static struct {
+	long val[8];
+} test_struct;
+static DEFINE_SEQLOCK(test_seqlock);
+
+/*
+ * Helper to avoid compiler optimizing out reads, and to generate source values
+ * for writes.
+ */
+__no_kcsan
+static noinline void sink_value(long v) { WRITE_ONCE(test_sink, v); }
+
+static noinline void test_kernel_read(void) { sink_value(test_var); }
+
+static noinline void test_kernel_write(void)
+{
+	test_var = READ_ONCE_NOCHECK(test_sink) + 1;
+}
+
+static noinline void test_kernel_write_nochange(void) { test_var = 42; }
+
+/* Suffixed by value-change exception filter. */
+static noinline void test_kernel_write_nochange_rcu(void) { test_var = 42; }
+
+static noinline void test_kernel_read_atomic(void)
+{
+	sink_value(READ_ONCE(test_var));
+}
+
+static noinline void test_kernel_write_atomic(void)
+{
+	WRITE_ONCE(test_var, READ_ONCE_NOCHECK(test_sink) + 1);
+}
+
+static noinline void test_kernel_atomic_rmw(void)
+{
+	/* Use builtin, so we can set up the "bad" atomic/non-atomic scenario. */
+	__atomic_fetch_add(&test_var, 1, __ATOMIC_RELAXED);
+}
+
+__no_kcsan
+static noinline void test_kernel_write_uninstrumented(void) { test_var++; }
+
+static noinline void test_kernel_data_race(void) { data_race(test_var++); }
+
+static noinline void test_kernel_assert_writer(void)
+{
+	ASSERT_EXCLUSIVE_WRITER(test_var);
+}
+
+static noinline void test_kernel_assert_access(void)
+{
+	ASSERT_EXCLUSIVE_ACCESS(test_var);
+}
+
+#define TEST_CHANGE_BITS 0xff00ff00
+
+static noinline void test_kernel_change_bits(void)
+{
+	if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {
+		/*
+		 * Avoid race of unknown origin for this test, just pretend they
+		 * are atomic.
+		 */
+		kcsan_nestable_atomic_begin();
+		test_var ^= TEST_CHANGE_BITS;
+		kcsan_nestable_atomic_end();
+	} else
+		WRITE_ONCE(test_var, READ_ONCE(test_var) ^ TEST_CHANGE_BITS);
+}
+
+static noinline void test_kernel_assert_bits_change(void)
+{
+	ASSERT_EXCLUSIVE_BITS(test_var, TEST_CHANGE_BITS);
+}
+
+static noinline void test_kernel_assert_bits_nochange(void)
+{
+	ASSERT_EXCLUSIVE_BITS(test_var, ~TEST_CHANGE_BITS);
+}
+
+/* To check that scoped assertions do trigger anywhere in scope. */
+static noinline void test_enter_scope(void)
+{
+	int x = 0;
+
+	/* Unrelated accesses to scoped assert. */
+	READ_ONCE(test_sink);
+	kcsan_check_read(&x, sizeof(x));
+}
+
+static noinline void test_kernel_assert_writer_scoped(void)
+{
+	ASSERT_EXCLUSIVE_WRITER_SCOPED(test_var);
+	test_enter_scope();
+}
+
+static noinline void test_kernel_assert_access_scoped(void)
+{
+	ASSERT_EXCLUSIVE_ACCESS_SCOPED(test_var);
+	test_enter_scope();
+}
+
+static noinline void test_kernel_rmw_array(void)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(test_array); ++i)
+		test_array[i]++;
+}
+
+static noinline void test_kernel_write_struct(void)
+{
+	kcsan_check_write(&test_struct, sizeof(test_struct));
+	kcsan_disable_current();
+	test_struct.val[3]++; /* induce value change */
+	kcsan_enable_current();
+}
+
+static noinline void test_kernel_write_struct_part(void)
+{
+	test_struct.val[3] = 42;
+}
+
+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;
+
+	do {
+		seq = read_seqbegin(&test_seqlock);
+		sink_value(test_var);
+	} while (read_seqretry(&test_seqlock, seq));
+}
+
+static noinline void test_kernel_seqlock_writer(void)
+{
+	unsigned long flags;
+
+	write_seqlock_irqsave(&test_seqlock, flags);
+	test_var++;
+	write_sequnlock_irqrestore(&test_seqlock, flags);
+}
+
+static noinline void test_kernel_atomic_builtins(void)
+{
+	/*
+	 * Generate concurrent accesses, expecting no reports, ensuring KCSAN
+	 * treats builtin atomics as actually atomic.
+	 */
+	__atomic_load_n(&test_var, __ATOMIC_RELAXED);
+}
+
+/* ===== Test cases ===== */
+
+/* Simple test with normal data race. */
+__no_kcsan
+static void test_basic(struct kunit *test)
+{
+	const struct expect_report expect = {
+		.access = {
+			{ test_kernel_write, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
+			{ test_kernel_read, &test_var, sizeof(test_var), 0 },
+		},
+	};
+	static const struct expect_report never = {
+		.access = {
+			{ test_kernel_read, &test_var, sizeof(test_var), 0 },
+			{ test_kernel_read, &test_var, sizeof(test_var), 0 },
+		},
+	};
+	bool match_expect = false;
+	bool match_never = false;
+
+	begin_test_checks(test_kernel_write, test_kernel_read);
+	do {
+		match_expect |= report_matches(&expect);
+		match_never = report_matches(&never);
+	} while (!end_test_checks(match_never));
+	KUNIT_EXPECT_TRUE(test, match_expect);
+	KUNIT_EXPECT_FALSE(test, match_never);
+}
+
+/*
+ * Stress KCSAN with lots of concurrent races on different addresses until
+ * timeout.
+ */
+__no_kcsan
+static void test_concurrent_races(struct kunit *test)
+{
+	const struct expect_report expect = {
+		.access = {
+			/* NULL will match any address. */
+			{ test_kernel_rmw_array, NULL, 0, __KCSAN_ACCESS_RW(KCSAN_ACCESS_WRITE) },
+			{ test_kernel_rmw_array, NULL, 0, __KCSAN_ACCESS_RW(0) },
+		},
+	};
+	static const struct expect_report never = {
+		.access = {
+			{ test_kernel_rmw_array, NULL, 0, 0 },
+			{ test_kernel_rmw_array, NULL, 0, 0 },
+		},
+	};
+	bool match_expect = false;
+	bool match_never = false;
+
+	begin_test_checks(test_kernel_rmw_array, test_kernel_rmw_array);
+	do {
+		match_expect |= report_matches(&expect);
+		match_never |= report_matches(&never);
+	} while (!end_test_checks(false));
+	KUNIT_EXPECT_TRUE(test, match_expect); /* Sanity check matches exist. */
+	KUNIT_EXPECT_FALSE(test, match_never);
+}
+
+/* Test the KCSAN_REPORT_VALUE_CHANGE_ONLY option. */
+__no_kcsan
+static void test_novalue_change(struct kunit *test)
+{
+	const struct expect_report expect = {
+		.access = {
+			{ test_kernel_write_nochange, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
+			{ test_kernel_read, &test_var, sizeof(test_var), 0 },
+		},
+	};
+	bool match_expect = false;
+
+	begin_test_checks(test_kernel_write_nochange, test_kernel_read);
+	do {
+		match_expect = report_matches(&expect);
+	} while (!end_test_checks(match_expect));
+	if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY))
+		KUNIT_EXPECT_FALSE(test, match_expect);
+	else
+		KUNIT_EXPECT_TRUE(test, match_expect);
+}
+
+/*
+ * Test that the rules where the KCSAN_REPORT_VALUE_CHANGE_ONLY option should
+ * never apply work.
+ */
+__no_kcsan
+static void test_novalue_change_exception(struct kunit *test)
+{
+	const struct expect_report expect = {
+		.access = {
+			{ test_kernel_write_nochange_rcu, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
+			{ test_kernel_read, &test_var, sizeof(test_var), 0 },
+		},
+	};
+	bool match_expect = false;
+
+	begin_test_checks(test_kernel_write_nochange_rcu, test_kernel_read);
+	do {
+		match_expect = report_matches(&expect);
+	} while (!end_test_checks(match_expect));
+	KUNIT_EXPECT_TRUE(test, match_expect);
+}
+
+/* Test that data races of unknown origin are reported. */
+__no_kcsan
+static void test_unknown_origin(struct kunit *test)
+{
+	const struct expect_report expect = {
+		.access = {
+			{ test_kernel_read, &test_var, sizeof(test_var), 0 },
+			{ NULL },
+		},
+	};
+	bool match_expect = false;
+
+	begin_test_checks(test_kernel_write_uninstrumented, test_kernel_read);
+	do {
+		match_expect = report_matches(&expect);
+	} while (!end_test_checks(match_expect));
+	if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN))
+		KUNIT_EXPECT_TRUE(test, match_expect);
+	else
+		KUNIT_EXPECT_FALSE(test, match_expect);
+}
+
+/* Test KCSAN_ASSUME_PLAIN_WRITES_ATOMIC if it is selected. */
+__no_kcsan
+static void test_write_write_assume_atomic(struct kunit *test)
+{
+	const struct expect_report expect = {
+		.access = {
+			{ test_kernel_write, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
+			{ test_kernel_write, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
+		},
+	};
+	bool match_expect = false;
+
+	begin_test_checks(test_kernel_write, test_kernel_write);
+	do {
+		sink_value(READ_ONCE(test_var)); /* induce value-change */
+		match_expect = report_matches(&expect);
+	} while (!end_test_checks(match_expect));
+	if (IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC))
+		KUNIT_EXPECT_FALSE(test, match_expect);
+	else
+		KUNIT_EXPECT_TRUE(test, match_expect);
+}
+
+/*
+ * Test that data races with writes larger than word-size are always reported,
+ * even if KCSAN_ASSUME_PLAIN_WRITES_ATOMIC is selected.
+ */
+__no_kcsan
+static void test_write_write_struct(struct kunit *test)
+{
+	const struct expect_report expect = {
+		.access = {
+			{ test_kernel_write_struct, &test_struct, sizeof(test_struct), KCSAN_ACCESS_WRITE },
+			{ test_kernel_write_struct, &test_struct, sizeof(test_struct), KCSAN_ACCESS_WRITE },
+		},
+	};
+	bool match_expect = false;
+
+	begin_test_checks(test_kernel_write_struct, test_kernel_write_struct);
+	do {
+		match_expect = report_matches(&expect);
+	} while (!end_test_checks(match_expect));
+	KUNIT_EXPECT_TRUE(test, match_expect);
+}
+
+/*
+ * Test that data races where only one write is larger than word-size are always
+ * reported, even if KCSAN_ASSUME_PLAIN_WRITES_ATOMIC is selected.
+ */
+__no_kcsan
+static void test_write_write_struct_part(struct kunit *test)
+{
+	const struct expect_report expect = {
+		.access = {
+			{ test_kernel_write_struct, &test_struct, sizeof(test_struct), KCSAN_ACCESS_WRITE },
+			{ test_kernel_write_struct_part, &test_struct.val[3], sizeof(test_struct.val[3]), KCSAN_ACCESS_WRITE },
+		},
+	};
+	bool match_expect = false;
+
+	begin_test_checks(test_kernel_write_struct, test_kernel_write_struct_part);
+	do {
+		match_expect = report_matches(&expect);
+	} while (!end_test_checks(match_expect));
+	KUNIT_EXPECT_TRUE(test, match_expect);
+}
+
+/* Test that races with atomic accesses never result in reports. */
+__no_kcsan
+static void test_read_atomic_write_atomic(struct kunit *test)
+{
+	bool match_never = false;
+
+	begin_test_checks(test_kernel_read_atomic, test_kernel_write_atomic);
+	do {
+		match_never = report_available();
+	} while (!end_test_checks(match_never));
+	KUNIT_EXPECT_FALSE(test, match_never);
+}
+
+/* Test that a race with an atomic and plain access result in reports. */
+__no_kcsan
+static void test_read_plain_atomic_write(struct kunit *test)
+{
+	const struct expect_report expect = {
+		.access = {
+			{ test_kernel_read, &test_var, sizeof(test_var), 0 },
+			{ test_kernel_write_atomic, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC },
+		},
+	};
+	bool match_expect = false;
+
+	if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS))
+		return;
+
+	begin_test_checks(test_kernel_read, test_kernel_write_atomic);
+	do {
+		match_expect = report_matches(&expect);
+	} while (!end_test_checks(match_expect));
+	KUNIT_EXPECT_TRUE(test, match_expect);
+}
+
+/* Test that atomic RMWs generate correct report. */
+__no_kcsan
+static void test_read_plain_atomic_rmw(struct kunit *test)
+{
+	const struct expect_report expect = {
+		.access = {
+			{ test_kernel_read, &test_var, sizeof(test_var), 0 },
+			{ test_kernel_atomic_rmw, &test_var, sizeof(test_var),
+				KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC },
+		},
+	};
+	bool match_expect = false;
+
+	if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS))
+		return;
+
+	begin_test_checks(test_kernel_read, test_kernel_atomic_rmw);
+	do {
+		match_expect = report_matches(&expect);
+	} while (!end_test_checks(match_expect));
+	KUNIT_EXPECT_TRUE(test, match_expect);
+}
+
+/* Zero-sized accesses should never cause data race reports. */
+__no_kcsan
+static void test_zero_size_access(struct kunit *test)
+{
+	const struct expect_report expect = {
+		.access = {
+			{ test_kernel_write_struct, &test_struct, sizeof(test_struct), KCSAN_ACCESS_WRITE },
+			{ test_kernel_write_struct, &test_struct, sizeof(test_struct), KCSAN_ACCESS_WRITE },
+		},
+	};
+	const struct expect_report never = {
+		.access = {
+			{ test_kernel_write_struct, &test_struct, sizeof(test_struct), KCSAN_ACCESS_WRITE },
+			{ test_kernel_read_struct_zero_size, &test_struct.val[3], 0, 0 },
+		},
+	};
+	bool match_expect = false;
+	bool match_never = false;
+
+	begin_test_checks(test_kernel_write_struct, test_kernel_read_struct_zero_size);
+	do {
+		match_expect |= report_matches(&expect);
+		match_never = report_matches(&never);
+	} while (!end_test_checks(match_never));
+	KUNIT_EXPECT_TRUE(test, match_expect); /* Sanity check. */
+	KUNIT_EXPECT_FALSE(test, match_never);
+}
+
+/* Test the data_race() macro. */
+__no_kcsan
+static void test_data_race(struct kunit *test)
+{
+	bool match_never = false;
+
+	begin_test_checks(test_kernel_data_race, test_kernel_data_race);
+	do {
+		match_never = report_available();
+	} while (!end_test_checks(match_never));
+	KUNIT_EXPECT_FALSE(test, match_never);
+}
+
+__no_kcsan
+static void test_assert_exclusive_writer(struct kunit *test)
+{
+	const struct expect_report expect = {
+		.access = {
+			{ test_kernel_assert_writer, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT },
+			{ test_kernel_write_nochange, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
+		},
+	};
+	bool match_expect = false;
+
+	begin_test_checks(test_kernel_assert_writer, test_kernel_write_nochange);
+	do {
+		match_expect = report_matches(&expect);
+	} while (!end_test_checks(match_expect));
+	KUNIT_EXPECT_TRUE(test, match_expect);
+}
+
+__no_kcsan
+static void test_assert_exclusive_access(struct kunit *test)
+{
+	const struct expect_report expect = {
+		.access = {
+			{ test_kernel_assert_access, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE },
+			{ test_kernel_read, &test_var, sizeof(test_var), 0 },
+		},
+	};
+	bool match_expect = false;
+
+	begin_test_checks(test_kernel_assert_access, test_kernel_read);
+	do {
+		match_expect = report_matches(&expect);
+	} while (!end_test_checks(match_expect));
+	KUNIT_EXPECT_TRUE(test, match_expect);
+}
+
+__no_kcsan
+static void test_assert_exclusive_access_writer(struct kunit *test)
+{
+	const struct expect_report expect_access_writer = {
+		.access = {
+			{ test_kernel_assert_access, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE },
+			{ test_kernel_assert_writer, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT },
+		},
+	};
+	const struct expect_report expect_access_access = {
+		.access = {
+			{ test_kernel_assert_access, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE },
+			{ test_kernel_assert_access, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE },
+		},
+	};
+	const struct expect_report never = {
+		.access = {
+			{ test_kernel_assert_writer, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT },
+			{ test_kernel_assert_writer, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT },
+		},
+	};
+	bool match_expect_access_writer = false;
+	bool match_expect_access_access = false;
+	bool match_never = false;
+
+	begin_test_checks(test_kernel_assert_access, test_kernel_assert_writer);
+	do {
+		match_expect_access_writer |= report_matches(&expect_access_writer);
+		match_expect_access_access |= report_matches(&expect_access_access);
+		match_never |= report_matches(&never);
+	} while (!end_test_checks(match_never));
+	KUNIT_EXPECT_TRUE(test, match_expect_access_writer);
+	KUNIT_EXPECT_TRUE(test, match_expect_access_access);
+	KUNIT_EXPECT_FALSE(test, match_never);
+}
+
+__no_kcsan
+static void test_assert_exclusive_bits_change(struct kunit *test)
+{
+	const struct expect_report expect = {
+		.access = {
+			{ test_kernel_assert_bits_change, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT },
+			{ test_kernel_change_bits, &test_var, sizeof(test_var),
+				KCSAN_ACCESS_WRITE | (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) ? 0 : KCSAN_ACCESS_ATOMIC) },
+		},
+	};
+	bool match_expect = false;
+
+	begin_test_checks(test_kernel_assert_bits_change, test_kernel_change_bits);
+	do {
+		match_expect = report_matches(&expect);
+	} while (!end_test_checks(match_expect));
+	KUNIT_EXPECT_TRUE(test, match_expect);
+}
+
+__no_kcsan
+static void test_assert_exclusive_bits_nochange(struct kunit *test)
+{
+	bool match_never = false;
+
+	begin_test_checks(test_kernel_assert_bits_nochange, test_kernel_change_bits);
+	do {
+		match_never = report_available();
+	} while (!end_test_checks(match_never));
+	KUNIT_EXPECT_FALSE(test, match_never);
+}
+
+__no_kcsan
+static void test_assert_exclusive_writer_scoped(struct kunit *test)
+{
+	const struct expect_report expect_start = {
+		.access = {
+			{ test_kernel_assert_writer_scoped, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_SCOPED },
+			{ test_kernel_write_nochange, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
+		},
+	};
+	const struct expect_report expect_anywhere = {
+		.access = {
+			{ test_enter_scope, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_SCOPED },
+			{ test_kernel_write_nochange, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
+		},
+	};
+	bool match_expect_start = false;
+	bool match_expect_anywhere = false;
+
+	begin_test_checks(test_kernel_assert_writer_scoped, test_kernel_write_nochange);
+	do {
+		match_expect_start |= report_matches(&expect_start);
+		match_expect_anywhere |= report_matches(&expect_anywhere);
+	} while (!end_test_checks(match_expect_start && match_expect_anywhere));
+	KUNIT_EXPECT_TRUE(test, match_expect_start);
+	KUNIT_EXPECT_TRUE(test, match_expect_anywhere);
+}
+
+__no_kcsan
+static void test_assert_exclusive_access_scoped(struct kunit *test)
+{
+	const struct expect_report expect_start1 = {
+		.access = {
+			{ test_kernel_assert_access_scoped, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_SCOPED },
+			{ test_kernel_read, &test_var, sizeof(test_var), 0 },
+		},
+	};
+	const struct expect_report expect_start2 = {
+		.access = { expect_start1.access[0], expect_start1.access[0] },
+	};
+	const struct expect_report expect_inscope = {
+		.access = {
+			{ test_enter_scope, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_SCOPED },
+			{ test_kernel_read, &test_var, sizeof(test_var), 0 },
+		},
+	};
+	bool match_expect_start = false;
+	bool match_expect_inscope = false;
+
+	begin_test_checks(test_kernel_assert_access_scoped, test_kernel_read);
+	end_time += msecs_to_jiffies(1000); /* This test requires a bit more time. */
+	do {
+		match_expect_start |= report_matches(&expect_start1) || report_matches(&expect_start2);
+		match_expect_inscope |= report_matches(&expect_inscope);
+	} while (!end_test_checks(match_expect_start && match_expect_inscope));
+	KUNIT_EXPECT_TRUE(test, match_expect_start);
+	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)
+{
+	bool match_never = false;
+
+	begin_test_checks(test_kernel_seqlock_reader, test_kernel_seqlock_writer);
+	do {
+		match_never = report_available();
+	} while (!end_test_checks(match_never));
+	KUNIT_EXPECT_FALSE(test, match_never);
+}
+
+/*
+ * Test atomic builtins work and required instrumentation functions exist. We
+ * also test that KCSAN understands they're atomic by racing with them via
+ * test_kernel_atomic_builtins(), and expect no reports.
+ *
+ * The atomic builtins _SHOULD NOT_ be used in normal kernel code!
+ */
+static void test_atomic_builtins(struct kunit *test)
+{
+	bool match_never = false;
+
+	begin_test_checks(test_kernel_atomic_builtins, test_kernel_atomic_builtins);
+	do {
+		long tmp;
+
+		kcsan_enable_current();
+
+		__atomic_store_n(&test_var, 42L, __ATOMIC_RELAXED);
+		KUNIT_EXPECT_EQ(test, 42L, __atomic_load_n(&test_var, __ATOMIC_RELAXED));
+
+		KUNIT_EXPECT_EQ(test, 42L, __atomic_exchange_n(&test_var, 20, __ATOMIC_RELAXED));
+		KUNIT_EXPECT_EQ(test, 20L, test_var);
+
+		tmp = 20L;
+		KUNIT_EXPECT_TRUE(test, __atomic_compare_exchange_n(&test_var, &tmp, 30L,
+								    0, __ATOMIC_RELAXED,
+								    __ATOMIC_RELAXED));
+		KUNIT_EXPECT_EQ(test, tmp, 20L);
+		KUNIT_EXPECT_EQ(test, test_var, 30L);
+		KUNIT_EXPECT_FALSE(test, __atomic_compare_exchange_n(&test_var, &tmp, 40L,
+								     1, __ATOMIC_RELAXED,
+								     __ATOMIC_RELAXED));
+		KUNIT_EXPECT_EQ(test, tmp, 30L);
+		KUNIT_EXPECT_EQ(test, test_var, 30L);
+
+		KUNIT_EXPECT_EQ(test, 30L, __atomic_fetch_add(&test_var, 1, __ATOMIC_RELAXED));
+		KUNIT_EXPECT_EQ(test, 31L, __atomic_fetch_sub(&test_var, 1, __ATOMIC_RELAXED));
+		KUNIT_EXPECT_EQ(test, 30L, __atomic_fetch_and(&test_var, 0xf, __ATOMIC_RELAXED));
+		KUNIT_EXPECT_EQ(test, 14L, __atomic_fetch_xor(&test_var, 0xf, __ATOMIC_RELAXED));
+		KUNIT_EXPECT_EQ(test, 1L, __atomic_fetch_or(&test_var, 0xf0, __ATOMIC_RELAXED));
+		KUNIT_EXPECT_EQ(test, 241L, __atomic_fetch_nand(&test_var, 0xf, __ATOMIC_RELAXED));
+		KUNIT_EXPECT_EQ(test, -2L, test_var);
+
+		__atomic_thread_fence(__ATOMIC_SEQ_CST);
+		__atomic_signal_fence(__ATOMIC_SEQ_CST);
+
+		kcsan_disable_current();
+
+		match_never = report_available();
+	} while (!end_test_checks(match_never));
+	KUNIT_EXPECT_FALSE(test, match_never);
+}
+
+/*
+ * Each test case is run with different numbers of threads. Until KUnit supports
+ * passing arguments for each test case, we encode #threads in the test case
+ * name (read by get_num_threads()). [The '-' was chosen as a stylistic
+ * preference to separate test name and #threads.]
+ *
+ * The thread counts are chosen to cover potentially interesting boundaries and
+ * corner cases (range 2-5), and then stress the system with larger counts.
+ */
+#define KCSAN_KUNIT_CASE(test_name)                                            \
+	{ .run_case = test_name, .name = #test_name "-02" },                   \
+	{ .run_case = test_name, .name = #test_name "-03" },                   \
+	{ .run_case = test_name, .name = #test_name "-04" },                   \
+	{ .run_case = test_name, .name = #test_name "-05" },                   \
+	{ .run_case = test_name, .name = #test_name "-08" },                   \
+	{ .run_case = test_name, .name = #test_name "-16" }
+
+static struct kunit_case kcsan_test_cases[] = {
+	KCSAN_KUNIT_CASE(test_basic),
+	KCSAN_KUNIT_CASE(test_concurrent_races),
+	KCSAN_KUNIT_CASE(test_novalue_change),
+	KCSAN_KUNIT_CASE(test_novalue_change_exception),
+	KCSAN_KUNIT_CASE(test_unknown_origin),
+	KCSAN_KUNIT_CASE(test_write_write_assume_atomic),
+	KCSAN_KUNIT_CASE(test_write_write_struct),
+	KCSAN_KUNIT_CASE(test_write_write_struct_part),
+	KCSAN_KUNIT_CASE(test_read_atomic_write_atomic),
+	KCSAN_KUNIT_CASE(test_read_plain_atomic_write),
+	KCSAN_KUNIT_CASE(test_read_plain_atomic_rmw),
+	KCSAN_KUNIT_CASE(test_zero_size_access),
+	KCSAN_KUNIT_CASE(test_data_race),
+	KCSAN_KUNIT_CASE(test_assert_exclusive_writer),
+	KCSAN_KUNIT_CASE(test_assert_exclusive_access),
+	KCSAN_KUNIT_CASE(test_assert_exclusive_access_writer),
+	KCSAN_KUNIT_CASE(test_assert_exclusive_bits_change),
+	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),
+	KCSAN_KUNIT_CASE(test_atomic_builtins),
+	{},
+};
+
+/* ===== End test cases ===== */
+
+/* Get number of threads encoded in test name. */
+static bool __no_kcsan
+get_num_threads(const char *test, int *nthreads)
+{
+	int len = strlen(test);
+
+	if (WARN_ON(len < 3))
+		return false;
+
+	*nthreads = test[len - 1] - '0';
+	*nthreads += (test[len - 2] - '0') * 10;
+
+	if (WARN_ON(*nthreads < 0))
+		return false;
+
+	return true;
+}
+
+/* Concurrent accesses from interrupts. */
+__no_kcsan
+static void access_thread_timer(struct timer_list *timer)
+{
+	static atomic_t cnt = ATOMIC_INIT(0);
+	unsigned int idx;
+	void (*func)(void);
+
+	idx = (unsigned int)atomic_inc_return(&cnt) % ARRAY_SIZE(access_kernels);
+	/* Acquire potential initialization. */
+	func = smp_load_acquire(&access_kernels[idx]);
+	if (func)
+		func();
+}
+
+/* The main loop for each thread. */
+__no_kcsan
+static int access_thread(void *arg)
+{
+	struct timer_list timer;
+	unsigned int cnt = 0;
+	unsigned int idx;
+	void (*func)(void);
+
+	timer_setup_on_stack(&timer, access_thread_timer, 0);
+	do {
+		might_sleep();
+
+		if (!timer_pending(&timer))
+			mod_timer(&timer, jiffies + 1);
+		else {
+			/* Iterate through all kernels. */
+			idx = cnt++ % ARRAY_SIZE(access_kernels);
+			/* Acquire potential initialization. */
+			func = smp_load_acquire(&access_kernels[idx]);
+			if (func)
+				func();
+		}
+	} while (!torture_must_stop());
+	del_timer_sync(&timer);
+	destroy_timer_on_stack(&timer);
+
+	torture_kthread_stopping("access_thread");
+	return 0;
+}
+
+__no_kcsan
+static int test_init(struct kunit *test)
+{
+	unsigned long flags;
+	int nthreads;
+	int i;
+
+	spin_lock_irqsave(&observed.lock, flags);
+	for (i = 0; i < ARRAY_SIZE(observed.lines); ++i)
+		observed.lines[i][0] = '\0';
+	observed.nlines = 0;
+	spin_unlock_irqrestore(&observed.lock, flags);
+
+	if (!torture_init_begin((char *)test->name, 1))
+		return -EBUSY;
+
+	if (!get_num_threads(test->name, &nthreads))
+		goto err;
+
+	if (WARN_ON(threads))
+		goto err;
+
+	for (i = 0; i < ARRAY_SIZE(access_kernels); ++i) {
+		if (WARN_ON(access_kernels[i]))
+			goto err;
+	}
+
+	if (!IS_ENABLED(CONFIG_PREEMPT) || !IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER)) {
+		/*
+		 * Without any preemption, keep 2 CPUs free for other tasks, one
+		 * of which is the main test case function checking for
+		 * completion or failure.
+		 */
+		const int min_unused_cpus = IS_ENABLED(CONFIG_PREEMPT_NONE) ? 2 : 0;
+		const int min_required_cpus = 2 + min_unused_cpus;
+
+		if (num_online_cpus() < min_required_cpus) {
+			pr_err("%s: too few online CPUs (%u < %d) for test",
+			       test->name, num_online_cpus(), min_required_cpus);
+			goto err;
+		} else if (nthreads > num_online_cpus() - min_unused_cpus) {
+			nthreads = num_online_cpus() - min_unused_cpus;
+			pr_warn("%s: limiting number of threads to %d\n",
+				test->name, nthreads);
+		}
+	}
+
+	if (nthreads) {
+		threads = kcalloc(nthreads + 1, sizeof(struct task_struct *),
+				  GFP_KERNEL);
+		if (WARN_ON(!threads))
+			goto err;
+
+		threads[nthreads] = NULL;
+		for (i = 0; i < nthreads; ++i) {
+			if (torture_create_kthread(access_thread, NULL,
+						   threads[i]))
+				goto err;
+		}
+	}
+
+	torture_init_end();
+
+	return 0;
+
+err:
+	kfree(threads);
+	threads = NULL;
+	torture_init_end();
+	return -EINVAL;
+}
+
+__no_kcsan
+static void test_exit(struct kunit *test)
+{
+	struct task_struct **stop_thread;
+	int i;
+
+	if (torture_cleanup_begin())
+		return;
+
+	for (i = 0; i < ARRAY_SIZE(access_kernels); ++i)
+		WRITE_ONCE(access_kernels[i], NULL);
+
+	if (threads) {
+		for (stop_thread = threads; *stop_thread; stop_thread++)
+			torture_stop_kthread(reader_thread, *stop_thread);
+
+		kfree(threads);
+		threads = NULL;
+	}
+
+	torture_cleanup_end();
+}
+
+static struct kunit_suite kcsan_test_suite = {
+	.name = "kcsan",
+	.test_cases = kcsan_test_cases,
+	.init = test_init,
+	.exit = test_exit,
+};
+static struct kunit_suite *kcsan_test_suites[] = { &kcsan_test_suite, NULL };
+
+__no_kcsan
+static void register_tracepoints(struct tracepoint *tp, void *ignore)
+{
+	check_trace_callback_type_console(probe_console);
+	if (!strcmp(tp->name, "console"))
+		WARN_ON(tracepoint_probe_register(tp, probe_console, NULL));
+}
+
+__no_kcsan
+static void unregister_tracepoints(struct tracepoint *tp, void *ignore)
+{
+	if (!strcmp(tp->name, "console"))
+		tracepoint_probe_unregister(tp, probe_console, NULL);
+}
+
+/*
+ * We only want to do tracepoints setup and teardown once, therefore we have to
+ * customize the init and exit functions and cannot rely on kunit_test_suite().
+ */
+static int __init kcsan_test_init(void)
+{
+	/*
+	 * Because we want to be able to build the test as a module, we need to
+	 * iterate through all known tracepoints, since the static registration
+	 * won't work here.
+	 */
+	for_each_kernel_tracepoint(register_tracepoints, NULL);
+	return __kunit_test_suites_init(kcsan_test_suites);
+}
+
+static void kcsan_test_exit(void)
+{
+	__kunit_test_suites_exit(kcsan_test_suites);
+	for_each_kernel_tracepoint(unregister_tracepoints, NULL);
+	tracepoint_synchronize_unregister();
+}
+
+late_initcall(kcsan_test_init);
+module_exit(kcsan_test_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Marco Elver <elver@google.com>");