[PATCH v2] tracing/osnoise: fix potential deadlock in cpu hotplug

[hu.shengming]

From: Luo Haiyang <luo.haiyang@xxxxxxxxxx>

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).

Signed-off-by: Luo Haiyang <luo.haiyang@xxxxxxxxxx>

---

Changes in v2:

- update change log

- Link to v1: https://lore.kernel.org/all/20260324150616953rMo1BWtAZ1nXTNrEFP6hr@xxxxxxxxxx/

---

 kernel/trace/trace_osnoise.c | 10 +++++-----

 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c

index dee610e465b9..be6cf0bb3c03 100644

--- a/kernel/trace/trace_osnoise.c

+++ b/kernel/trace/trace_osnoise.c

@@ -2073,8 +2073,8 @@ static void osnoise_hotplug_workfn(struct work_struct *dummy)

  if (!osnoise_has_registered_instances())

  return;

 

- guard(mutex)(&interface_lock);

  guard(cpus_read_lock)();

+ guard(mutex)(&interface_lock);

 

  if (!cpu_online(cpu))

  return;

@@ -2237,11 +2237,11 @@ static ssize_t osnoise_options_write(struct file *filp, const char __user *ubuf,

  if (running)

  stop_per_cpu_kthreads();

 

- mutex_lock(&interface_lock);

  /*

  * avoid CPU hotplug operations that might read options.

  */

  cpus_read_lock();

+ mutex_lock(&interface_lock);

 

  retval = cnt;

 

@@ -2257,8 +2257,8 @@ static ssize_t osnoise_options_write(struct file *filp, const char __user *ubuf,

  clear_bit(option, &osnoise_options);

  }

 

- cpus_read_unlock();

  mutex_unlock(&interface_lock);

+ cpus_read_unlock();

 

  if (running)

  start_per_cpu_kthreads();

@@ -2345,16 +2345,16 @@ osnoise_cpus_write(struct file *filp, const char __user *ubuf, size_t count,

  if (running)

  stop_per_cpu_kthreads();

 

- 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)

  start_per_cpu_kthreads();

-- 

2.25.1