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From:   Ian Rogers <irogers@google.com>
Date:   Fri, 26 Aug 2022 09:06:20 -0700
Message-ID: <CAP-5=fXk+mLv=C0CTrvnBeuhCTAtJ=x2O8D2YqvmVZSMHqcLvQ@mail.gmail.com>
Subject: Re: [PATCH v3 16/18] perf sched: Fixes for thread safety analysis
To:     Adrian Hunter <adrian.hunter@intel.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
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On Fri, Aug 26, 2022 at 5:12 AM Adrian Hunter <adrian.hunter@intel.com> wrote:
>
> On 24/08/22 18:38, Ian Rogers wrote:
> > Add annotations to describe lock behavior. Add unlocks so that mutexes
> > aren't conditionally held on exit from perf_sched__replay. Add an exit
> > variable so that thread_func can terminate, rather than leaving the
> > threads blocked on mutexes.
> >
> > Signed-off-by: Ian Rogers <irogers@google.com>
> > ---
> >  tools/perf/builtin-sched.c | 46 ++++++++++++++++++++++++--------------
> >  1 file changed, 29 insertions(+), 17 deletions(-)
> >
> > diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
> > index 7e4006d6b8bc..b483ff0d432e 100644
> > --- a/tools/perf/builtin-sched.c
> > +++ b/tools/perf/builtin-sched.c
> > @@ -246,6 +246,7 @@ struct perf_sched {
> >       const char      *time_str;
> >       struct perf_time_interval ptime;
> >       struct perf_time_interval hist_time;
> > +     volatile bool   thread_funcs_exit;
> >  };
> >
> >  /* per thread run time data */
> > @@ -633,31 +634,34 @@ static void *thread_func(void *ctx)
> >       prctl(PR_SET_NAME, comm2);
> >       if (fd < 0)
> >               return NULL;
> > -again:
> > -     ret = sem_post(&this_task->ready_for_work);
> > -     BUG_ON(ret);
> > -     mutex_lock(&sched->start_work_mutex);
> > -     mutex_unlock(&sched->start_work_mutex);
> >
> > -     cpu_usage_0 = get_cpu_usage_nsec_self(fd);
> > +     while (!sched->thread_funcs_exit) {
> > +             ret = sem_post(&this_task->ready_for_work);
> > +             BUG_ON(ret);
> > +             mutex_lock(&sched->start_work_mutex);
> > +             mutex_unlock(&sched->start_work_mutex);
> >
> > -     for (i = 0; i < this_task->nr_events; i++) {
> > -             this_task->curr_event = i;
> > -             perf_sched__process_event(sched, this_task->atoms[i]);
> > -     }
> > +             cpu_usage_0 = get_cpu_usage_nsec_self(fd);
> >
> > -     cpu_usage_1 = get_cpu_usage_nsec_self(fd);
> > -     this_task->cpu_usage = cpu_usage_1 - cpu_usage_0;
> > -     ret = sem_post(&this_task->work_done_sem);
> > -     BUG_ON(ret);
> > +             for (i = 0; i < this_task->nr_events; i++) {
> > +                     this_task->curr_event = i;
> > +                     perf_sched__process_event(sched, this_task->atoms[i]);
> > +             }
> >
> > -     mutex_lock(&sched->work_done_wait_mutex);
> > -     mutex_unlock(&sched->work_done_wait_mutex);
> > +             cpu_usage_1 = get_cpu_usage_nsec_self(fd);
> > +             this_task->cpu_usage = cpu_usage_1 - cpu_usage_0;
> > +             ret = sem_post(&this_task->work_done_sem);
> > +             BUG_ON(ret);
> >
> > -     goto again;
> > +             mutex_lock(&sched->work_done_wait_mutex);
> > +             mutex_unlock(&sched->work_done_wait_mutex);
> > +     }
> > +     return NULL;
> >  }
> >
> >  static void create_tasks(struct perf_sched *sched)
> > +     EXCLUSIVE_LOCK_FUNCTION(sched->start_work_mutex)
> > +     EXCLUSIVE_LOCK_FUNCTION(sched->work_done_wait_mutex)
> >  {
> >       struct task_desc *task;
> >       pthread_attr_t attr;
> > @@ -687,6 +691,8 @@ static void create_tasks(struct perf_sched *sched)
> >  }
> >
> >  static void wait_for_tasks(struct perf_sched *sched)
> > +     EXCLUSIVE_LOCKS_REQUIRED(sched->work_done_wait_mutex)
> > +     EXCLUSIVE_LOCKS_REQUIRED(sched->start_work_mutex)
> >  {
> >       u64 cpu_usage_0, cpu_usage_1;
> >       struct task_desc *task;
> > @@ -738,6 +744,8 @@ static void wait_for_tasks(struct perf_sched *sched)
> >  }
> >
> >  static void run_one_test(struct perf_sched *sched)
> > +     EXCLUSIVE_LOCKS_REQUIRED(sched->work_done_wait_mutex)
> > +     EXCLUSIVE_LOCKS_REQUIRED(sched->start_work_mutex)
> >  {
> >       u64 T0, T1, delta, avg_delta, fluct;
> >
> > @@ -3309,11 +3317,15 @@ static int perf_sched__replay(struct perf_sched *sched)
> >       print_task_traces(sched);
> >       add_cross_task_wakeups(sched);
> >
> > +     sched->thread_funcs_exit = false;
> >       create_tasks(sched);
> >       printf("------------------------------------------------------------\n");
> >       for (i = 0; i < sched->replay_repeat; i++)
> >               run_one_test(sched);
> >
> > +     sched->thread_funcs_exit = true;
> > +     mutex_unlock(&sched->start_work_mutex);
> > +     mutex_unlock(&sched->work_done_wait_mutex);
>
> I think you still need to wait for the threads to exit before
> destroying the mutexes.

This is a pre-existing issue and beyond the scope of this patch set.

Thanks,
Ian

> >       return 0;
> >  }
> >
>