trace/hwlat: Protect kdata->kthread with get/put_online_cpus

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

Link: https://lore.kernel.org/linux-doc/20210621134636.5b332226@oasis.local.home/
Link: https://lkml.kernel.org/r/8bdb2a56f46abfd301d6fffbf43448380c09a6f5.1624372313.git.bristot@redhat.com
Cc: Phil Auld <pauld@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Clark Willaims <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Suggested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index a625bfd..20e31f7 100644 (file)
--- 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;
 }