Merge tag 'trace-v4.11-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull another tracing update from Steven Rostedt:
 "Commit 79c6f448 ("tracing: Fix hwlat kthread migration") fixed a
  bug that was caused by a race condition in initializing the hwlat
  thread. When fixing this code, I realized that it should have been
  done differently. Instead of doing the rewrite and sending that to
  stable, I just sent the above commit to fix the bug that should be
  back ported.

  This commit is on top of the quick fix commit to rewrite the code the
  way it should have been written in the first place"

* tag 'trace-v4.11-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Clean up the hwlat binding code

kernel/trace/trace_hwlat.c

@@ -266,24 +266,13 @@ static int get_sample(void)
 static struct cpumask save_cpumask;
 static bool disable_migrate;
 
-static void move_to_next_cpu(bool initmask)
+static void move_to_next_cpu(void)
 {
-	static struct cpumask *current_mask;
+	struct cpumask *current_mask = &save_cpumask;
 	int next_cpu;
 
 	if (disable_migrate)
 		return;
-
-	/* Just pick the first CPU on first iteration */
-	if (initmask) {
-		current_mask = &save_cpumask;
-		get_online_cpus();
-		cpumask_and(current_mask, cpu_online_mask, tracing_buffer_mask);
-		put_online_cpus();
-		next_cpu = cpumask_first(current_mask);
-		goto set_affinity;
-	}
-
 	/*
 	 * If for some reason the user modifies the CPU affinity
 	 * of this thread, than stop migrating for the duration
@@ -300,7 +289,6 @@ static void move_to_next_cpu(bool initmask)
 	if (next_cpu >= nr_cpu_ids)
 		next_cpu = cpumask_first(current_mask);
 
- set_affinity:
 	if (next_cpu >= nr_cpu_ids) /* Shouldn't happen! */
 		goto disable;
 
@@ -327,12 +315,10 @@ static void move_to_next_cpu(bool initmask)
 static int kthread_fn(void *data)
 {
 	u64 interval;
-	bool initmask = true;
 
 	while (!kthread_should_stop()) {
 
-		move_to_next_cpu(initmask);
-		initmask = false;
+		move_to_next_cpu();
 
 		local_irq_disable();
 		get_sample();
@@ -363,13 +349,27 @@ static int kthread_fn(void *data)
  */
 static int start_kthread(struct trace_array *tr)
 {
+	struct cpumask *current_mask = &save_cpumask;
 	struct task_struct *kthread;
+	int next_cpu;
+
+	/* Just pick the first CPU on first iteration */
+	current_mask = &save_cpumask;
+	get_online_cpus();
+	cpumask_and(current_mask, cpu_online_mask, tracing_buffer_mask);
+	put_online_cpus();
+	next_cpu = cpumask_first(current_mask);
 
 	kthread = kthread_create(kthread_fn, NULL, "hwlatd");
 	if (IS_ERR(kthread)) {
 		pr_err(BANNER "could not start sampling thread\n");
 		return -ENOMEM;
 	}
+
+	cpumask_clear(current_mask);
+	cpumask_set_cpu(next_cpu, current_mask);
+	sched_setaffinity(kthread->pid, current_mask);
+
 	hwlat_kthread = kthread;
 	wake_up_process(kthread);