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

[Ian Rogers]

On Mon, Jul 4, 2022 at 8:10 AM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>
> On Mon, 4 Jul 2022 at 17:06, Marco Elver <elver@xxxxxxxxxx> 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@xxxxxxxxxx>
>
> Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>

Acked-by: Ian Rogers <irogers@xxxxxxxxxx>

Thanks,
Ian

> > ---
> > 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
> >