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

[Adrian Hunter]

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@xxxxxxxxxx>
> ---
>  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.

>  	return 0;
>  }
>