[PATCH 5.15.y] tracing: Fix potential deadlock in cpu hotplug with osnoise

[Sasha Levin <sashal@kernel.org>]

From: Luo Haiyang <luo.haiyang@zte.com.cn>

[ Upstream commit 1f9885732248d22f788e4992c739a98c88ab8a55 ]

The following sequence may leads deadlock in cpu hotplug:

    task1        task2        task3
    -----        -----        -----

 mutex_lock(&interface_lock)

            [CPU GOING OFFLINE]

            cpus_write_lock();
            osnoise_cpu_die();
              kthread_stop(task3);
                wait_for_completion();

                      osnoise_sleep();
                        mutex_lock(&interface_lock);

 cpus_read_lock();

 [DEAD LOCK]

Fix by swap the order of cpus_read_lock() and mutex_lock(&interface_lock).

Cc: stable@vger.kernel.org
Cc: <mathieu.desnoyers@efficios.com>
Cc: <zhang.run@zte.com.cn>
Cc: <yang.tao172@zte.com.cn>
Cc: <ran.xiaokai@zte.com.cn>
Fixes: bce29ac9ce0bb ("trace: Add osnoise tracer")
Link: https://patch.msgid.link/20260326141953414bVSj33dAYktqp9Oiyizq8@zte.com.cn
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Luo Haiyang <luo.haiyang@zte.com.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
[ adapted guard() macros to lock/unlock calls ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/trace/trace_osnoise.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 5959b1d4ee459..66061e77cc514 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -1620,8 +1620,8 @@ static void osnoise_hotplug_workfn(struct work_struct *dummy)
 	if (!osnoise_busy)
 		goto out_unlock_trace;
 
-	mutex_lock(&interface_lock);
 	cpus_read_lock();
+	mutex_lock(&interface_lock);
 
 	if (!cpu_online(cpu))
 		goto out_unlock;
@@ -1634,8 +1634,8 @@ static void osnoise_hotplug_workfn(struct work_struct *dummy)
 	start_kthread(cpu);
 
 out_unlock:
-	cpus_read_unlock();
 	mutex_unlock(&interface_lock);
+	cpus_read_unlock();
 out_unlock_trace:
 	mutex_unlock(&trace_types_lock);
 }
@@ -1772,16 +1772,16 @@ osnoise_cpus_write(struct file *filp, const char __user *ubuf, size_t count,
 	if (running)
 		osnoise_tracer_stop(tr);
 
-	mutex_lock(&interface_lock);
 	/*
 	 * osnoise_cpumask is read by CPU hotplug operations.
 	 */
 	cpus_read_lock();
+	mutex_lock(&interface_lock);
 
 	cpumask_copy(&osnoise_cpumask, osnoise_cpumask_new);
 
-	cpus_read_unlock();
 	mutex_unlock(&interface_lock);
+	cpus_read_unlock();
 
 	if (running)
 		osnoise_tracer_start(tr);
-- 
2.53.0