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

[hu.shengming]

From: luohaiyang10243395 <luo.haiy...@zte.com.cn>

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.haiy...@zte.com.cn>
---
 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