perf/hw_breakpoint: Add KUnit test for constraints accounting

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20220829124719.675715-2-elver@google.com

diff --git a/kernel/events/Makefile b/kernel/events/Makefile
index 8591c18..91a62f5 100644 (file)
--- 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 (file)
index 0000000..433c5c4
--- /dev/null
+++ b/kernel/events/hw_breakpoint_test.c
@@ -0,0 +1,323 @@
+// 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;
+
+       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_test_cpu(int num)
+{
+       int cpu;
+
+       WARN_ON(num < 0);
+
+       for_each_online_cpu(cpu) {
+               if (num-- <= 0)
+                       break;
+       }
+
+       return cpu;
+}
+
+/* ===== Test cases ===== */
+
+static void test_one_cpu(struct kunit *test)
+{
+       int idx = 0;
+
+       fill_bp_slots(test, &idx, get_test_cpu(0), NULL, 0);
+       TEST_EXPECT_NOSPC(register_test_bp(-1, current, idx));
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(0), 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(get_test_cpu(0), current, idx));
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(0), NULL, idx));
+       /* Remove one and adding back CPU-target should work. */
+       unregister_test_bp(&test_bps[0]);
+       fill_one_bp_slot(test, &idx, get_test_cpu(0), 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(get_test_cpu(0), current, idx));
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(0), get_other_task(test), idx));
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(0), 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(get_test_cpu(0), NULL, idx));
+}
+
+static void test_one_task_on_one_cpu(struct kunit *test)
+{
+       int idx = 0;
+
+       fill_bp_slots(test, &idx, get_test_cpu(0), current, 0);
+       TEST_EXPECT_NOSPC(register_test_bp(-1, current, idx));
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(0), current, idx));
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(0), 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, get_test_cpu(0), 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, get_test_cpu(0), current);
+       fill_bp_slots(test, &idx, -1, current, 1);
+       TEST_EXPECT_NOSPC(register_test_bp(-1, current, idx));
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(0), current, idx));
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(0), 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, get_test_cpu(0), NULL);
+       fill_one_bp_slot(test, &idx, get_test_cpu(0), NULL);
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(0), NULL, idx));
+}
+
+static void test_two_tasks_on_one_cpu(struct kunit *test)
+{
+       int idx = 0;
+
+       fill_bp_slots(test, &idx, get_test_cpu(0), current, 0);
+       fill_bp_slots(test, &idx, get_test_cpu(0), 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(get_test_cpu(0), current, idx));
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(0), get_other_task(test), idx));
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(0), NULL, idx));
+       /* Can still create breakpoints on some other CPU. */
+       fill_bp_slots(test, &idx, get_test_cpu(1), NULL, 0);
+}
+
+static void test_two_tasks_on_one_all_cpus(struct kunit *test)
+{
+       int idx = 0;
+
+       fill_bp_slots(test, &idx, get_test_cpu(0), 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(get_test_cpu(0), current, idx));
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(0), get_other_task(test), idx));
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(0), NULL, idx));
+       /* Cannot create breakpoints on some other CPU either. */
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(1), 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, get_test_cpu(0), current);
+       fill_one_bp_slot(test, &idx, -1, current);
+
+       TEST_EXPECT_NOSPC(register_test_bp(-1, current, idx));
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(0), current, idx));
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(0), NULL, idx));
+
+       /* We should still be able to use up another CPU's slots. */
+       cpu_idx = idx;
+       fill_one_bp_slot(test, &idx, get_test_cpu(1), NULL);
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(1), 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_test_cpu(1). */
+       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(get_test_cpu(0), current, idx));
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(0), NULL, idx));
+       TEST_EXPECT_NOSPC(register_test_bp(get_test_cpu(1), 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 072e4b2..863b517 100644 (file)
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2530,6 +2530,16 @@ 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