Re: [PATCH v6 3/5] cxl: Fix device reference leak in cxl_port_perf_data_calculate()

[Dave Jiang <dave.jiang@intel.com>]

On 1/5/24 15:56, Robert Richter wrote:
> See inline.
> 
> On 05.01.24 15:07:46, Dave Jiang wrote:
>> cxl_port_perf_data_calculate() calls find_cxl_root() and does not
>> dereference the 'struct device' in the cxl_root->port. find_cxl_root()
>> calls get_device() and takes a reference on the port 'struct device'
>> member. Use the __free() macro to ensure the dereference happens.
>>
>> Fixes: 7a4f148dd8d5 ("cxl: Compute the entire CXL path latency and bandwidth data")
>> Reviewed-by: Ira Weiny <ira.weiny@intel.com>
>> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
>> ---
>> v5:
>> - Update patch title (Dan)
>> ---
>>  drivers/cxl/core/cdat.c |    7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/cxl/core/cdat.c b/drivers/cxl/core/cdat.c
>> index 0df5379cf02f..c6208aab452f 100644
>> --- a/drivers/cxl/core/cdat.c
>> +++ b/drivers/cxl/core/cdat.c
>> @@ -162,7 +162,6 @@ static int cxl_port_perf_data_calculate(struct cxl_port *port,
>>  					struct xarray *dsmas_xa)
>>  {
>>  	struct access_coordinate c;
>> -	struct cxl_root *cxl_root;
>>  	struct dsmas_entry *dent;
>>  	int valid_entries = 0;
>>  	unsigned long index;
>> @@ -174,7 +173,11 @@ static int cxl_port_perf_data_calculate(struct cxl_port *port,
>>  		return rc;
>>  	}
>>  
>> -	cxl_root = find_cxl_root(port);
>> +	struct cxl_root *cxl_root __free(put_cxl_root) = find_cxl_root(port);
> 
> I am not quite sure here, can a definition in the middle of a block?
> At least this is uncommon.

From what I understand with the introduction of the scope-based resource management, this kind of declaration is ok for that purpose? Dan?

> 
>> +
>> +	if (!cxl_root)
>> +		return -ENODEV;
> 
> As Dan pointed out earlier, isn't there always a root port in the
> hierarchy? So the check could be dropped?
> 
>> +
>>  	if (!cxl_root->ops || !cxl_root->ops->qos_class)
>>  		return -EOPNOTSUPP;
>>  
>>
>>