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

Adrian Hunter
2022-08-26T12:12:58Z

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.

> return 0;
> }
>