Re: [PATCH v3 16/18] perf sched: Fixes for thread safety analysis

[Adrian Hunter <adrian.hunter@intel.com>]

On 26/08/22 19:06, Ian Rogers wrote:
> 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.

You added the mutex_destroy functions in patch 8, so it is still
fallout from that.

> 
> Thanks,
> Ian
> 
>>>       return 0;
>>>  }
>>>
>>