[PATCH v4 02/14] perf/hw_breakpoint: Provide hw_breakpoint_is_used() and use in test

From: Marco Elver
Date: Mon Aug 29 2022 - 08:57:03 EST


Provide hw_breakpoint_is_used() to check if breakpoints are in use on
the system.

Use it in the KUnit test to verify the global state before and after a
test case.

Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Acked-by: Ian Rogers <irogers@xxxxxxxxxx>
---
v3:
* New patch.
---
include/linux/hw_breakpoint.h | 3 +++
kernel/events/hw_breakpoint.c | 29 +++++++++++++++++++++++++++++
kernel/events/hw_breakpoint_test.c | 12 +++++++++++-
3 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h
index 78dd7035d1e5..a3fb846705eb 100644
--- a/include/linux/hw_breakpoint.h
+++ b/include/linux/hw_breakpoint.h
@@ -74,6 +74,7 @@ register_wide_hw_breakpoint(struct perf_event_attr *attr,
extern int register_perf_hw_breakpoint(struct perf_event *bp);
extern void unregister_hw_breakpoint(struct perf_event *bp);
extern void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events);
+extern bool hw_breakpoint_is_used(void);

extern int dbg_reserve_bp_slot(struct perf_event *bp);
extern int dbg_release_bp_slot(struct perf_event *bp);
@@ -121,6 +122,8 @@ register_perf_hw_breakpoint(struct perf_event *bp) { return -ENOSYS; }
static inline void unregister_hw_breakpoint(struct perf_event *bp) { }
static inline void
unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events) { }
+static inline bool hw_breakpoint_is_used(void) { return false; }
+
static inline int
reserve_bp_slot(struct perf_event *bp) {return -ENOSYS; }
static inline void release_bp_slot(struct perf_event *bp) { }
diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index f32320ac02fd..fd5cd1f9e7fc 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -604,6 +604,35 @@ void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events)
}
EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);

+/**
+ * hw_breakpoint_is_used - check if breakpoints are currently used
+ *
+ * Returns: true if breakpoints are used, false otherwise.
+ */
+bool hw_breakpoint_is_used(void)
+{
+ int cpu;
+
+ if (!constraints_initialized)
+ return false;
+
+ for_each_possible_cpu(cpu) {
+ for (int type = 0; type < TYPE_MAX; ++type) {
+ struct bp_cpuinfo *info = get_bp_info(cpu, type);
+
+ if (info->cpu_pinned)
+ return true;
+
+ for (int slot = 0; slot < nr_slots[type]; ++slot) {
+ if (info->tsk_pinned[slot])
+ return true;
+ }
+ }
+ }
+
+ return false;
+}
+
static struct notifier_block hw_breakpoint_exceptions_nb = {
.notifier_call = hw_breakpoint_exceptions_notify,
/* we need to be notified first */
diff --git a/kernel/events/hw_breakpoint_test.c b/kernel/events/hw_breakpoint_test.c
index 433c5c45e2a5..5ced822df788 100644
--- a/kernel/events/hw_breakpoint_test.c
+++ b/kernel/events/hw_breakpoint_test.c
@@ -294,7 +294,14 @@ static struct kunit_case hw_breakpoint_test_cases[] = {
static int test_init(struct kunit *test)
{
/* Most test cases want 2 distinct CPUs. */
- return num_online_cpus() < 2 ? -EINVAL : 0;
+ if (num_online_cpus() < 2)
+ return -EINVAL;
+
+ /* Want the system to not use breakpoints elsewhere. */
+ if (hw_breakpoint_is_used())
+ return -EBUSY;
+
+ return 0;
}

static void test_exit(struct kunit *test)
@@ -308,6 +315,9 @@ static void test_exit(struct kunit *test)
kthread_stop(__other_task);
__other_task = NULL;
}
+
+ /* Verify that internal state agrees that no breakpoints are in use. */
+ KUNIT_EXPECT_FALSE(test, hw_breakpoint_is_used());
}

static struct kunit_suite hw_breakpoint_test_suite = {
--
2.37.2.672.g94769d06f0-goog