linux-kernel - Re: [PATCH 3/3] kcsan: Add atomic builtin test case

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Date:   Mon, 6 Jul 2020 16:45:11 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Marco Elver <elver@...gle.com>
Cc:     dvyukov@...gle.com, glider@...gle.com, andreyknvl@...gle.com,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] kcsan: Add atomic builtin test case

On Fri, Jul 03, 2020 at 03:40:31PM +0200, Marco Elver wrote:
> Adds test case to kcsan-test module, to test atomic builtin
> instrumentation works.
> 
> Signed-off-by: Marco Elver <elver@...gle.com>

Applied all three, thank you!!!

							Thanx, Paul

> ---
>  kernel/kcsan/kcsan-test.c | 63 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 63 insertions(+)
> 
> diff --git a/kernel/kcsan/kcsan-test.c b/kernel/kcsan/kcsan-test.c
> index fed6fcb5768c..721180cbbab1 100644
> --- a/kernel/kcsan/kcsan-test.c
> +++ b/kernel/kcsan/kcsan-test.c
> @@ -390,6 +390,15 @@ static noinline void test_kernel_seqlock_writer(void)
>  	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. */
> @@ -852,6 +861,59 @@ static void test_seqlock_noreport(struct kunit *test)
>  	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
> @@ -891,6 +953,7 @@ static struct kunit_case kcsan_test_cases[] = {
>  	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),
>  	{},
>  };
>  
> -- 
> 2.27.0.212.ge8ba1cc988-goog
>