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

Ian Rogers
2022-08-26T16:06:40Z

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;
> > }
> >
>