[PATCH V5 11/14] trace/hwlat: Protect kdata->kthread with get/put_online_cpus

[Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>]

In preparation to the hotplug support, protect kdata->kthread
with get/put_online_cpus() to avoid concurrency with hotplug
operations.

Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
Cc: Clark Willaims <williams@xxxxxxxxxx>
Cc: John Kacur <jkacur@xxxxxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
---
 kernel/trace/trace_hwlat.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index 8756ab24c132..dc30b8a9bd5f 100644
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -396,13 +396,19 @@ static int kthread_fn(void *data)
 static void stop_single_kthread(void)
 {
 	struct hwlat_kthread_data *kdata = get_cpu_data();
-	struct task_struct *kthread = kdata->kthread;
+	struct task_struct *kthread;
+
+	get_online_cpus();
+	kthread = kdata->kthread;
 
 	if (!kthread)
-		return;
+		goto out_put_cpus;
 
 	kthread_stop(kthread);
 	kdata->kthread = NULL;
+
+out_put_cpus:
+	put_online_cpus();
 }
 
 
@@ -419,20 +425,19 @@ static int start_single_kthread(struct trace_array *tr)
 	struct task_struct *kthread;
 	int next_cpu;
 
+	get_online_cpus();
 	if (kdata->kthread)
-		return 0;
+		goto out_put_cpus;
 
 	kthread = kthread_create(kthread_fn, NULL, "hwlatd");
 	if (IS_ERR(kthread)) {
 		pr_err(BANNER "could not start sampling thread\n");
+		put_online_cpus();
 		return -ENOMEM;
 	}
 
-
 	/* Just pick the first CPU on first iteration */
-	get_online_cpus();
 	cpumask_and(current_mask, cpu_online_mask, tr->tracing_cpumask);
-	put_online_cpus();
 
 	if (hwlat_data.thread_mode == MODE_ROUND_ROBIN) {
 		next_cpu = cpumask_first(current_mask);
@@ -446,6 +451,8 @@ static int start_single_kthread(struct trace_array *tr)
 	kdata->kthread = kthread;
 	wake_up_process(kthread);
 
+out_put_cpus:
+	put_online_cpus();
 	return 0;
 }
 
-- 
2.31.1