Re: [PATCH v3 02/14] perf/hw_breakpoint: Provide hw_breakpoint_is_used() and use in test

[Dmitry Vyukov <dvyukov@google.com>]

On Mon, 4 Jul 2022 at 17:06, Marco Elver <elver@google.com> wrote:
>
> 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@google.com>

Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

> ---
> 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 = {
> --
> 2.37.0.rc0.161.g10f37bed90-goog
>