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Date:   Fri, 26 Aug 2022 09:42:40 -0700
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Subject: [PATCH v4 16/18] perf sched: Fixes for thread safety analysis
From:   Ian Rogers <irogers@google.com>
To:     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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        Alexey Bayduraev <alexey.v.bayduraev@linux.intel.com>,
        Riccardo Mancini <rickyman7@gmail.com>,
        Andi Kleen <ak@linux.intel.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Zechuan Chen <chenzechuan1@huawei.com>,
        Jason Wang <wangborong@cdjrlc.com>,
        Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
        Remi Bernon <rbernon@codeweavers.com>,
        linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org,
        bpf@vger.kernel.org, llvm@lists.linux.dev
Cc:     Ian Rogers <irogers@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

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);
 	return 0;
 }
 
-- 
2.37.2.672.g94769d06f0-goog