Re: [PATCH v2] kcsan: Add test suite

[Paul E. McKenney]

On Tue, May 05, 2020 at 08:28:21PM +0200, Marco Elver wrote:
> This adds KCSAN test focusing on behaviour of the integrated runtime.
> Tests various race scenarios, and verifies the reports generated to
> console. Makes use of KUnit for test organization, and the Torture
> framework for test thread control.
> 
> Signed-off-by: Marco Elver <elver@xxxxxxxxxx>

I have replaced V1 with this update, thank you!

							Thanx, Paul

> ---
> v2:
> * Add necessary precondition checks that we have sufficient online CPUs
>   for PREEMPT_NONE, PREEMPT_VOLUNTARY, and PREEMPT without
>   KCSAN_INTERRUPT_WATCHER. This is to avoid deadlocking the system, or
>   resulting in flaky test results.
> * Adds the necessary might_sleep() for PREEMPT_VOLUNTARY.
> ---
>  kernel/kcsan/Makefile     |    3 +
>  kernel/kcsan/kcsan-test.c | 1084 +++++++++++++++++++++++++++++++++++++
>  lib/Kconfig.kcsan         |   23 +-
>  3 files changed, 1109 insertions(+), 1 deletion(-)
>  create mode 100644 kernel/kcsan/kcsan-test.c
> 
> diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
> index d4999b38d1be..14533cf24bc3 100644
> --- a/kernel/kcsan/Makefile
> +++ b/kernel/kcsan/Makefile
> @@ -12,3 +12,6 @@ CFLAGS_core.o := $(call cc-option,-fno-conserve-stack,) \
>  
>  obj-y := core.o debugfs.o report.o
>  obj-$(CONFIG_KCSAN_SELFTEST) += test.o
> +
> +CFLAGS_kcsan-test.o := $(CFLAGS_KCSAN) -g -fno-omit-frame-pointer
> +obj-$(CONFIG_KCSAN_TEST) += kcsan-test.o
> diff --git a/kernel/kcsan/kcsan-test.c b/kernel/kcsan/kcsan-test.c
> new file mode 100644
> index 000000000000..a8c11506dd2a
> --- /dev/null
> +++ b/kernel/kcsan/kcsan-test.c
> @@ -0,0 +1,1084 @@
> +// 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@xxxxxxxxxx>
> + */
> +
> +#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>
> +
> +/* 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_or_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_or_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 char *const access_type =
> +			(r->access[i].type & KCSAN_ACCESS_ASSERT) ?
> +				((r->access[i].type & KCSAN_ACCESS_WRITE) ?
> +					 "assert no accesses" :
> +					 "assert no writes") :
> +				((r->access[i].type & KCSAN_ACCESS_WRITE) ?
> +					 "write" :
> +					 "read");
> +		const char *const access_type_aux =
> +			(r->access[i].type & KCSAN_ACCESS_ATOMIC) ?
> +				" (marked)" :
> +				((r->access[i].type & 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);
> +}
> +
> +__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_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);
> +}
> +
> +/* ===== 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_WRITE },
> +			{ test_kernel_rmw_array, NULL, 0, 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);
> +}
> +
> +/* 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);
> +}
> +
> +/* 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);
> +}
> +
> +/*
> + * 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_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_seqlock_noreport),
> +	{},
> +};
> +
> +/* ===== 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",
> +	.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@xxxxxxxxxx>");
> diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
> index 689b6b81f272..ea28245c6c1d 100644
> --- a/lib/Kconfig.kcsan
> +++ b/lib/Kconfig.kcsan
> @@ -41,7 +41,28 @@ config KCSAN_SELFTEST
>  	bool "Perform short selftests on boot"
>  	default y
>  	help
> -	  Run KCSAN selftests on boot. On test failure, causes the kernel to panic.
> +	  Run KCSAN selftests on boot. On test failure, causes the kernel to
> +	  panic. Recommended to be enabled, ensuring critical functionality
> +	  works as intended.
> +
> +config KCSAN_TEST
> +	tristate "KCSAN test for integrated runtime behaviour"
> +	depends on TRACEPOINTS && KUNIT
> +	select TORTURE_TEST
> +	help
> +	  KCSAN test focusing on behaviour of the integrated runtime. Tests
> +	  various race scenarios, and verifies the reports generated to
> +	  console. Makes use of KUnit for test organization, and the Torture
> +	  framework for test thread control.
> +
> +	  Each test case may run at least up to KCSAN_REPORT_ONCE_IN_MS
> +	  milliseconds. Test run duration may be optimized by building the
> +	  kernel and KCSAN test with KCSAN_REPORT_ONCE_IN_MS set to a lower
> +	  than default value.
> +
> +	  Say Y here if you want the test to be built into the kernel and run
> +	  during boot; say M if you want the test to build as a module; say N
> +	  if you are unsure.
>  
>  config KCSAN_EARLY_ENABLE
>  	bool "Early enable during boot"
> -- 
> 2.26.2.526.g744177e7f7-goog
>