Re: [PATCH v2 01/13] perf/hw_breakpoint: Add KUnit test for constraints accounting

Dmitry Vyukov
2022-06-28T12:53:43Z

On Tue, 28 Jun 2022 at 11:59, Marco Elver <elver@google.com> wrote:
>
> Add KUnit test for hw_breakpoint constraints accounting, with various
> interesting mixes of breakpoint targets (some care was taken to catch
> interesting corner cases via bug-injection).
>
> The test cannot be built as a module because it requires access to
> hw_breakpoint_slots(), which is not inlinable or exported on all
> architectures.
>
> Signed-off-by: Marco Elver <elver@google.com>
> ---
> v2:
> * New patch.
> ---
> kernel/events/Makefile | 1 +
> kernel/events/hw_breakpoint_test.c | 321 +++++++++++++++++++++++++++++
> lib/Kconfig.debug | 10 +
> 3 files changed, 332 insertions(+)
> create mode 100644 kernel/events/hw_breakpoint_test.c
>
> diff --git a/kernel/events/Makefile b/kernel/events/Makefile
> index 8591c180b52b..91a62f566743 100644
> --- a/kernel/events/Makefile
> +++ b/kernel/events/Makefile
> @@ -2,4 +2,5 @@
> obj-y := core.o ring_buffer.o callchain.o
>
> obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o
> +obj-$(CONFIG_HW_BREAKPOINT_KUNIT_TEST) += hw_breakpoint_test.o
> obj-$(CONFIG_UPROBES) += uprobes.o
> diff --git a/kernel/events/hw_breakpoint_test.c b/kernel/events/hw_breakpoint_test.c
> new file mode 100644
> index 000000000000..747a0249a606
> --- /dev/null
> +++ b/kernel/events/hw_breakpoint_test.c
> @@ -0,0 +1,321 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KUnit test for hw_breakpoint constraints accounting logic.
> + *
> + * Copyright (C) 2022, Google LLC.
> + */
> +
> +#include <kunit/test.h>
> +#include <linux/cpumask.h>
> +#include <linux/hw_breakpoint.h>
> +#include <linux/kthread.h>
> +#include <linux/perf_event.h>
> +#include <asm/hw_breakpoint.h>
> +
> +#define TEST_REQUIRES_BP_SLOTS(test, slots) \
> + do { \
> + if ((slots) > get_test_bp_slots()) { \
> + kunit_skip((test), "Requires breakpoint slots: %d > %d", slots, \
> + get_test_bp_slots()); \
> + } \
> + } while (0)
> +
> +#define TEST_EXPECT_NOSPC(expr) KUNIT_EXPECT_EQ(test, -ENOSPC, PTR_ERR(expr))
> +
> +#define MAX_TEST_BREAKPOINTS 512
> +
> +static char break_vars[MAX_TEST_BREAKPOINTS];
> +static struct perf_event *test_bps[MAX_TEST_BREAKPOINTS];
> +static struct task_struct *__other_task;
> +
> +static struct perf_event *register_test_bp(int cpu, struct task_struct *tsk, int idx)
> +{
> + struct perf_event_attr attr = {};
> +
> + if (WARN_ON(idx < 0 || idx >= MAX_TEST_BREAKPOINTS))
> + return NULL;
> +
> + hw_breakpoint_init(&attr);
> + attr.bp_addr = (unsigned long)&break_vars[idx];
> + attr.bp_len = HW_BREAKPOINT_LEN_1;
> + attr.bp_type = HW_BREAKPOINT_RW;
> + return perf_event_create_kernel_counter(&attr, cpu, tsk, NULL, NULL);
> +}
> +
> +static void unregister_test_bp(struct perf_event **bp)
> +{
> + if (WARN_ON(IS_ERR(*bp)))
> + return;
> + if (WARN_ON(!*bp))
> + return;
> + unregister_hw_breakpoint(*bp);
> + *bp = NULL;
> +}
> +
> +static int get_test_bp_slots(void)
> +{
> + static int slots;

Why is this function needed? Is hw_breakpoint_slots() very slow?

> +
> + if (!slots)
> + slots = hw_breakpoint_slots(TYPE_DATA);
> +
> + return slots;
> +}
> +
> +static void fill_one_bp_slot(struct kunit *test, int *id, int cpu, struct task_struct *tsk)
> +{
> + struct perf_event *bp = register_test_bp(cpu, tsk, *id);
> +
> + KUNIT_ASSERT_NOT_NULL(test, bp);
> + KUNIT_ASSERT_FALSE(test, IS_ERR(bp));
> + KUNIT_ASSERT_NULL(test, test_bps[*id]);
> + test_bps[(*id)++] = bp;
> +}
> +
> +/*
> + * Fills up the given @cpu/@tsk with breakpoints, only leaving @skip slots free.
> + *
> + * Returns true if this can be called again, continuing at @id.
> + */
> +static bool fill_bp_slots(struct kunit *test, int *id, int cpu, struct task_struct *tsk, int skip)
> +{
> + for (int i = 0; i < get_test_bp_slots() - skip; ++i)
> + fill_one_bp_slot(test, id, cpu, tsk);
> +
> + return *id + get_test_bp_slots() <= MAX_TEST_BREAKPOINTS;
> +}
> +
> +static int dummy_kthread(void *arg)
> +{
> + return 0;
> +}
> +
> +static struct task_struct *get_other_task(struct kunit *test)
> +{
> + struct task_struct *tsk;
> +
> + if (__other_task)
> + return __other_task;
> +
> + tsk = kthread_create(dummy_kthread, NULL, "hw_breakpoint_dummy_task");
> + KUNIT_ASSERT_FALSE(test, IS_ERR(tsk));
> + __other_task = tsk;
> + return __other_task;
> +}
> +
> +static int get_other_cpu(void)
> +{
> + int cpu;
> +
> + for_each_online_cpu(cpu) {
> + if (cpu != raw_smp_processor_id())

Are we guaranteed to not be rescheduled in the middle of a test?
If not, can't get_other_cpu() return the same CPU that was returned by
raw_smp_processor_id() earlier in the test?

> + break;
> + }
> +
> + return cpu;
> +}
> +
> +/* ===== Test cases ===== */
> +
> +static void test_one_cpu(struct kunit *test)
> +{
> + int idx = 0;
> +
> + fill_bp_slots(test, &idx, raw_smp_processor_id(), NULL, 0);
> + TEST_EXPECT_NOSPC(register_test_bp(-1, current, idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), NULL, idx));
> +}
> +
> +static void test_many_cpus(struct kunit *test)
> +{
> + int idx = 0;
> + int cpu;
> +
> + /* Test that CPUs are independent. */
> + for_each_online_cpu(cpu) {
> + bool do_continue = fill_bp_slots(test, &idx, cpu, NULL, 0);
> +
> + TEST_EXPECT_NOSPC(register_test_bp(cpu, NULL, idx));
> + if (!do_continue)
> + break;
> + }
> +}
> +
> +static void test_one_task_on_all_cpus(struct kunit *test)
> +{
> + int idx = 0;
> +
> + fill_bp_slots(test, &idx, -1, current, 0);
> + TEST_EXPECT_NOSPC(register_test_bp(-1, current, idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), current, idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), NULL, idx));
> + /* Remove one and adding back CPU-target should work. */
> + unregister_test_bp(&test_bps[0]);
> + fill_one_bp_slot(test, &idx, raw_smp_processor_id(), NULL);
> +}
> +
> +static void test_two_tasks_on_all_cpus(struct kunit *test)
> +{
> + int idx = 0;
> +
> + /* Test that tasks are independent. */
> + fill_bp_slots(test, &idx, -1, current, 0);
> + fill_bp_slots(test, &idx, -1, get_other_task(test), 0);
> +
> + TEST_EXPECT_NOSPC(register_test_bp(-1, current, idx));
> + TEST_EXPECT_NOSPC(register_test_bp(-1, get_other_task(test), idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), current, idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), get_other_task(test), idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), NULL, idx));
> + /* Remove one from first task and adding back CPU-target should not work. */
> + unregister_test_bp(&test_bps[0]);
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), NULL, idx));
> +}
> +
> +static void test_one_task_on_one_cpu(struct kunit *test)
> +{
> + int idx = 0;
> +
> + fill_bp_slots(test, &idx, raw_smp_processor_id(), current, 0);
> + TEST_EXPECT_NOSPC(register_test_bp(-1, current, idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), current, idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), NULL, idx));
> + /*
> + * Remove one and adding back CPU-target should work; this case is
> + * special vs. above because the task's constraints are CPU-dependent.
> + */
> + unregister_test_bp(&test_bps[0]);
> + fill_one_bp_slot(test, &idx, raw_smp_processor_id(), NULL);
> +}
> +
> +static void test_one_task_mixed(struct kunit *test)
> +{
> + int idx = 0;
> +
> + TEST_REQUIRES_BP_SLOTS(test, 3);
> +
> + fill_one_bp_slot(test, &idx, raw_smp_processor_id(), current);
> + fill_bp_slots(test, &idx, -1, current, 1);
> + TEST_EXPECT_NOSPC(register_test_bp(-1, current, idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), current, idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), NULL, idx));
> +
> + /* Transition from CPU-dependent pinned count to CPU-independent. */
> + unregister_test_bp(&test_bps[0]);
> + unregister_test_bp(&test_bps[1]);
> + fill_one_bp_slot(test, &idx, raw_smp_processor_id(), NULL);
> + fill_one_bp_slot(test, &idx, raw_smp_processor_id(), NULL);
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), NULL, idx));
> +}
> +
> +static void test_two_tasks_on_one_cpu(struct kunit *test)
> +{
> + int idx = 0;
> +
> + fill_bp_slots(test, &idx, raw_smp_processor_id(), current, 0);
> + fill_bp_slots(test, &idx, raw_smp_processor_id(), get_other_task(test), 0);
> +
> + TEST_EXPECT_NOSPC(register_test_bp(-1, current, idx));
> + TEST_EXPECT_NOSPC(register_test_bp(-1, get_other_task(test), idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), current, idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), get_other_task(test), idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), NULL, idx));
> + /* Can still create breakpoints on some other CPU. */
> + fill_bp_slots(test, &idx, get_other_cpu(), NULL, 0);
> +}
> +
> +static void test_two_tasks_on_one_all_cpus(struct kunit *test)
> +{
> + int idx = 0;
> +
> + fill_bp_slots(test, &idx, raw_smp_processor_id(), current, 0);
> + fill_bp_slots(test, &idx, -1, get_other_task(test), 0);
> +
> + TEST_EXPECT_NOSPC(register_test_bp(-1, current, idx));
> + TEST_EXPECT_NOSPC(register_test_bp(-1, get_other_task(test), idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), current, idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), get_other_task(test), idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), NULL, idx));
> + /* Cannot create breakpoints on some other CPU either. */
> + TEST_EXPECT_NOSPC(register_test_bp(get_other_cpu(), NULL, idx));
> +}
> +
> +static void test_task_on_all_and_one_cpu(struct kunit *test)
> +{
> + int tsk_on_cpu_idx, cpu_idx;
> + int idx = 0;
> +
> + TEST_REQUIRES_BP_SLOTS(test, 3);
> +
> + fill_bp_slots(test, &idx, -1, current, 2);
> + /* Transitioning from only all CPU breakpoints to mixed. */
> + tsk_on_cpu_idx = idx;
> + fill_one_bp_slot(test, &idx, raw_smp_processor_id(), current);
> + fill_one_bp_slot(test, &idx, -1, current);
> +
> + TEST_EXPECT_NOSPC(register_test_bp(-1, current, idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), current, idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), NULL, idx));
> +
> + /* We should still be able to use up another CPU's slots. */
> + cpu_idx = idx;
> + fill_one_bp_slot(test, &idx, get_other_cpu(), NULL);
> + TEST_EXPECT_NOSPC(register_test_bp(get_other_cpu(), NULL, idx));
> +
> + /* Transitioning back to task target on all CPUs. */
> + unregister_test_bp(&test_bps[tsk_on_cpu_idx]);
> + /* Still have a CPU target breakpoint in get_other_cpu(). */
> + TEST_EXPECT_NOSPC(register_test_bp(-1, current, idx));
> + /* Remove it and try again. */
> + unregister_test_bp(&test_bps[cpu_idx]);
> + fill_one_bp_slot(test, &idx, -1, current);
> +
> + TEST_EXPECT_NOSPC(register_test_bp(-1, current, idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), current, idx));
> + TEST_EXPECT_NOSPC(register_test_bp(raw_smp_processor_id(), NULL, idx));
> + TEST_EXPECT_NOSPC(register_test_bp(get_other_cpu(), NULL, idx));
> +}
> +
> +static struct kunit_case hw_breakpoint_test_cases[] = {
> + KUNIT_CASE(test_one_cpu),
> + KUNIT_CASE(test_many_cpus),
> + KUNIT_CASE(test_one_task_on_all_cpus),
> + KUNIT_CASE(test_two_tasks_on_all_cpus),
> + KUNIT_CASE(test_one_task_on_one_cpu),
> + KUNIT_CASE(test_one_task_mixed),
> + KUNIT_CASE(test_two_tasks_on_one_cpu),
> + KUNIT_CASE(test_two_tasks_on_one_all_cpus),
> + KUNIT_CASE(test_task_on_all_and_one_cpu),
> + {},
> +};
> +
> +static int test_init(struct kunit *test)
> +{
> + /* Most test cases want 2 distinct CPUs. */
> + return num_online_cpus() < 2 ? -EINVAL : 0;
> +}
> +
> +static void test_exit(struct kunit *test)
> +{
> + for (int i = 0; i < MAX_TEST_BREAKPOINTS; ++i) {
> + if (test_bps[i])
> + unregister_test_bp(&test_bps[i]);
> + }
> +
> + if (__other_task) {
> + kthread_stop(__other_task);
> + __other_task = NULL;
> + }
> +}
> +
> +static struct kunit_suite hw_breakpoint_test_suite = {
> + .name = "hw_breakpoint",
> + .test_cases = hw_breakpoint_test_cases,
> + .init = test_init,
> + .exit = test_exit,
> +};
> +
> +kunit_test_suites(&hw_breakpoint_test_suite);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Marco Elver <elver@google.com>");
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 2e24db4bff19..4c87a6edf046 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -2513,6 +2513,16 @@ config STACKINIT_KUNIT_TEST
> CONFIG_GCC_PLUGIN_STRUCTLEAK, CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF,
> or CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL.
>
> +config HW_BREAKPOINT_KUNIT_TEST
> + bool "Test hw_breakpoint constraints accounting" if !KUNIT_ALL_TESTS
> + depends on HAVE_HW_BREAKPOINT
> + depends on KUNIT=y
> + default KUNIT_ALL_TESTS
> + help
> + Tests for hw_breakpoint constraints accounting.
> +
> + If unsure, say N.
> +
> config TEST_UDELAY
> tristate "udelay test driver"
> help
> --
> 2.37.0.rc0.161.g10f37bed90-goog
>