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

[yingchao deng]

On 09/09/2026 00:16, Leo Yan wrote:
> 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;
>   }
Agreed — module init/exit are serialized, so the mutex around cscfg_mgr 
alloc/free is unnecessary. Removing it from cscfg_dev_release() is the 
cleaner fix and also resolves
the deadlock. I'll send v2 with your suggested change.