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

[hu.shengming]

From: luohaiyang10243395 <luo.haiyang@xxxxxxxxxx>

The following sequence may leads deadlock in cpu hotplug:

  CPU0                        |  CPU1
                              |  schedule_work_on
                              |
  _cpu_down//set CPU1 offline |
  cpus_write_lock             |
                              |  osnoise_hotplug_workfn
                              |    mutex_lock(&interface_lock);
                              |    cpus_read_lock();  //wait cpu_hotplug_lock
                              |
                              |  cpuhp/1
                              |    osnoise_cpu_die
                              |      kthread_stop
                              |        wait_for_completion //wait osnoise/1 exit
                              |
                              |  osnoise/1
                              |    osnoise_sleep
                              |      mutex_lock(&interface_lock); //deadlock

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

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