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Subject[PATCH V5 11/14] trace/hwlat: Protect kdata->kthread with get/put_online_cpus
Date
In preparation to the hotplug support, protect kdata->kthread
with get/put_online_cpus() to avoid concurrency with hotplug
operations.

Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Steven Rostedt <rostedt@goodmis.org>
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
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
---
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
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