Re: [PATCH] coresight: syscfg: fix deadlock on device registration failure

[Leo Yan <leo.yan@arm.com>]

On Tue, Aug 25, 2026 at 09:47:17AM +0800, yingchao wrote:

> diff --git a/drivers/hwtracing/coresight/coresight-syscfg.c b/drivers/hwtracing/coresight/coresight-syscfg.c
> index 2bfdd7b45e49..d0e7e4720e46 100644
> --- a/drivers/hwtracing/coresight/coresight-syscfg.c
> +++ b/drivers/hwtracing/coresight/coresight-syscfg.c
> @@ -1210,8 +1210,14 @@ static int cscfg_create_device(void)
>  	dev->init_name = "cs_system_cfg";
>  
>  	err = device_register(dev);
> -	if (err)
> +	if (err) {
> +		/* put_device() triggers cscfg_dev_release() which takes
> +		 * cscfg_mutex, so drop the lock first to avoid deadlocking.
> +		 */
> +		mutex_unlock(&cscfg_mutex);
>  		put_device(dev);
> +		return err;
> +	}

As module init and exit are serialized by the kernel, I don't think we
need the mutex to protect the allocation and freeing of cscfg_mgr.

The mutex should only be used for exclusively access cscfg_mgr.
So how about the change below?

---8<---

diff --git a/drivers/hwtracing/coresight/coresight-syscfg.c b/drivers/hwtracing/coresight/coresight-syscfg.c
index 2bfdd7b45e49..2dd0b29f44e4 100644
--- a/drivers/hwtracing/coresight/coresight-syscfg.c
+++ b/drivers/hwtracing/coresight/coresight-syscfg.c
@@ -1173,27 +1173,21 @@ struct device *cscfg_device(void)
 /* Must have a release function or the kernel will complain on module unload */
 static void cscfg_dev_release(struct device *dev)
 {
-	mutex_lock(&cscfg_mutex);
 	kfree(cscfg_mgr);
 	cscfg_mgr = NULL;
-	mutex_unlock(&cscfg_mutex);
 }
 
 /* a device is needed to "own" some kernel elements such as sysfs entries.  */
 static int cscfg_create_device(void)
 {
 	struct device *dev;
-	int err = -ENOMEM;
-
-	mutex_lock(&cscfg_mutex);
-	if (cscfg_mgr) {
-		err = -EINVAL;
-		goto create_dev_exit_unlock;
-	}
+	int err;
 
 	cscfg_mgr = kzalloc_obj(struct cscfg_manager);
 	if (!cscfg_mgr)
-		goto create_dev_exit_unlock;
+		return -ENOMEM;
+
+	mutex_lock(&cscfg_mutex);
 
 	/* initialise the cscfg_mgr structure */
 	INIT_LIST_HEAD(&cscfg_mgr->csdev_desc_list);
@@ -1204,6 +1198,8 @@ static int cscfg_create_device(void)
 	cscfg_mgr->load_state = CSCFG_NONE;
 	raw_spin_lock_init(&cscfg_mgr->sysfs_store_lock);
 
+	mutex_unlock(&cscfg_mutex);
+
 	/* setup the device */
 	dev = cscfg_device();
 	dev->release = cscfg_dev_release;
@@ -1213,8 +1209,6 @@ static int cscfg_create_device(void)
 	if (err)
 		put_device(dev);
 
-create_dev_exit_unlock:
-	mutex_unlock(&cscfg_mutex);
 	return err;
 }