[for-linus][PATCH] tracing: Fix potential deadlock in cpu hotplug with osnoise

[Steven Rostedt]

tracing fixes for 7.0:

- Fix potential deadlock in osnoise and hotplug

  The interface_lock can be called by a osnoise thread and the CPU shutdown
  logic of osnoise can wait for this thread to finish. But cpus_read_lock()
  can also be taken while holding the interface_lock. This produces a
  circular lock dependency and can cause a deadlock.

  Swap the ordering of cpus_read_lock() and the interface_lock to have
  interface_lock taken within the cpus_read_lock() context to prevent this
  circular dependency.

  git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git
trace/fixes

Head SHA1: 1f9885732248d22f788e4992c739a98c88ab8a55


Luo Haiyang (1):
      tracing: Fix potential deadlock in cpu hotplug with osnoise

----
 kernel/trace/trace_osnoise.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)
---------------------------
commit 1f9885732248d22f788e4992c739a98c88ab8a55
Author: Luo Haiyang <luo.haiyang@xxxxxxxxxx>
Date:   Thu Mar 26 14:19:53 2026 +0800

    tracing: Fix potential deadlock in cpu hotplug with osnoise
    
    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@xxxxxxxxxxxxxxx
    Cc: <mathieu.desnoyers@xxxxxxxxxxxx>
    Cc: <zhang.run@xxxxxxxxxx>
    Cc: <yang.tao172@xxxxxxxxxx>
    Cc: <ran.xiaokai@xxxxxxxxxx>
    Fixes: bce29ac9ce0bb ("trace: Add osnoise tracer")
    Link: https://patch.msgid.link/20260326141953414bVSj33dAYktqp9Oiyizq8@xxxxxxxxxx
    Reviewed-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
    Signed-off-by: Luo Haiyang <luo.haiyang@xxxxxxxxxx>
    Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>

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();