Re: [PATCH] drivers: use __free attribute instead of of_node_put()

[Vincenzo Mezzela <vincenzo.mezzela@gmail.com>]

On 19/04/24 16:01, Sudeep Holla wrote:
> On Fri, Apr 19, 2024 at 03:19:56PM +0200, Vincenzo Mezzela wrote:
>> Introduce the __free attribute for scope-based resource management.
>> Resources allocated with __free are automatically released at the end of
>> the scope. This enhancement aims to mitigate memory management issues
>> associated with forgetting to release resources by utilizing __free
>> instead of of_node_put().
>>
>> The declaration of the device_node used within the do-while loops is
>> moved directly within the loop so that the resource is automatically
>> freed at the end of each iteration.
>>
>> Suggested-by: Julia Lawall <julia.lawall@inria.fr>
>> Signed-off-by: Vincenzo Mezzela <vincenzo.mezzela@gmail.com>
>> ---
>>   drivers/base/arch_topology.c | 41 ++++++++++++++----------------------
>>   1 file changed, 16 insertions(+), 25 deletions(-)
>>
>> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
>> index 024b78a0cfc1..58eeb8183747 100644
>> --- a/drivers/base/arch_topology.c
>> +++ b/drivers/base/arch_topology.c
>> @@ -513,10 +513,10 @@ core_initcall(free_raw_capacity);
>>    */
>>   static int __init get_cpu_for_node(struct device_node *node)
>>   {
>> -	struct device_node *cpu_node;
>>   	int cpu;
>>
>> -	cpu_node = of_parse_phandle(node, "cpu", 0);
>> +	struct device_node *cpu_node __free(device_node) =
> Missing include <linux/cleanup.h> for this ?
>
>> +		of_parse_phandle(node, "cpu", 0);
>>   	if (!cpu_node)
>>   		return -1;
>>
>> @@ -527,7 +527,6 @@ static int __init get_cpu_for_node(struct device_node *node)
>>   		pr_info("CPU node for %pOF exist but the possible cpu range is :%*pbl\n",
>>   			cpu_node, cpumask_pr_args(cpu_possible_mask));
>>
>> -	of_node_put(cpu_node);
>>   	return cpu;
>>   }
>>
>> @@ -538,11 +537,11 @@ static int __init parse_core(struct device_node *core, int package_id,
>>   	bool leaf = true;
>>   	int i = 0;
>>   	int cpu;
>> -	struct device_node *t;
>>
>>   	do {
>>   		snprintf(name, sizeof(name), "thread%d", i);
>> -		t = of_get_child_by_name(core, name);
>> +		struct device_node *t __free(device_node) =
>> +			of_get_child_by_name(core, name);
>>   		if (t) {
>>   			leaf = false;
>>   			cpu = get_cpu_for_node(t);
>> @@ -553,10 +552,8 @@ static int __init parse_core(struct device_node *core, int package_id,
>>   				cpu_topology[cpu].thread_id = i;
>>   			} else if (cpu != -ENODEV) {
>>   				pr_err("%pOF: Can't get CPU for thread\n", t);
>> -				of_node_put(t);
>>   				return -EINVAL;
>>   			}
>> -			of_node_put(t);
> OK you moved 't' inside the loop and this must be taken care, but...
>
>>   		}
>>   		i++;
>>   	} while (t);
> ....now, will it even compile if 't' is not in scope ? I think you might get
> compilation here. If not, I still don't understand what is the value of
> 't' being checked there.
>
>> @@ -586,7 +583,6 @@ static int __init parse_cluster(struct device_node *cluster, int package_id,
>>   	char name[20];
>>   	bool leaf = true;
>>   	bool has_cores = false;
>> -	struct device_node *c;
>>   	int core_id = 0;
>>   	int i, ret;
>>
>> @@ -598,13 +594,13 @@ static int __init parse_cluster(struct device_node *cluster, int package_id,
>>   	i = 0;
>>   	do {
>>   		snprintf(name, sizeof(name), "cluster%d", i);
>> -		c = of_get_child_by_name(cluster, name);
>> +		struct device_node *c __free(device_node) =
>> +			of_get_child_by_name(cluster, name);
>>   		if (c) {
>>   			leaf = false;
>>   			ret = parse_cluster(c, package_id, i, depth + 1);
>>   			if (depth > 0)
>>   				pr_warn("Topology for clusters of clusters not yet supported\n");
>> -			of_node_put(c);
>>   			if (ret != 0)
>>   				return ret;
>>   		}
>> @@ -615,14 +611,14 @@ static int __init parse_cluster(struct device_node *cluster, int package_id,
>>   	i = 0;
>>   	do {
>>   		snprintf(name, sizeof(name), "core%d", i);
>> -		c = of_get_child_by_name(cluster, name);
>> +		struct device_node *c __free(device_node) =
>> +			of_get_child_by_name(cluster, name);
>>   		if (c) {
>>   			has_cores = true;
>>
>>   			if (depth == 0) {
>>   				pr_err("%pOF: cpu-map children should be clusters\n",
>>   				       c);
>> -				of_node_put(c);
>>   				return -EINVAL;
>>   			}
>>
>> @@ -635,7 +631,6 @@ static int __init parse_cluster(struct device_node *cluster, int package_id,
>>   				ret = -EINVAL;
>>   			}
>>
>> -			of_node_put(c);
>>   			if (ret != 0)
>>   				return ret;
>>   		}
>> @@ -651,17 +646,16 @@ static int __init parse_cluster(struct device_node *cluster, int package_id,
>>   static int __init parse_socket(struct device_node *socket)
>>   {
>>   	char name[20];
>> -	struct device_node *c;
>>   	bool has_socket = false;
>>   	int package_id = 0, ret;
>>
>>   	do {
>>   		snprintf(name, sizeof(name), "socket%d", package_id);
>> -		c = of_get_child_by_name(socket, name);
>> +		struct device_node *c __free(device_node) =
>> +			of_get_child_by_name(socket, name);
>>   		if (c) {
>>   			has_socket = true;
>>   			ret = parse_cluster(c, package_id, -1, 0);
>> -			of_node_put(c);
>>   			if (ret != 0)
>>   				return ret;
>>   		}
> Same thing applies to these while(c) loop. I don't understand how this
> could work even if it is compiling fine which I doubt.
>
>> @@ -676,11 +670,11 @@ static int __init parse_socket(struct device_node *socket)
>>
>>   static int __init parse_dt_topology(void)
>>   {
>> -	struct device_node *cn, *map;
>>   	int ret = 0;
>>   	int cpu;
>>
>> -	cn = of_find_node_by_path("/cpus");
>> +	struct device_node *cn __free(device_node) =
>> +		of_find_node_by_path("/cpus");
>>   	if (!cn) {
>>   		pr_err("No CPU information found in DT\n");
>>   		return 0;
>> @@ -690,13 +684,14 @@ static int __init parse_dt_topology(void)
>>   	 * When topology is provided cpu-map is essentially a root
>>   	 * cluster with restricted subnodes.
>>   	 */
>> -	map = of_get_child_by_name(cn, "cpu-map");
>> +	struct device_node *map __free(devide_node) =
> If not above ones, this must fail to compile. Perhaps s/devide_node/device_node/ ?
> I now doubt if this patch is compile tested ?
>
> --
> Regards,
> Sudeep

Hi,

As you rightly pointed out, I inadvertently omitted to compile this file 
during the kernel build process. Consequently, certain errors remained 
undetected. I apologize for the oversight.

I'll send an updated version of this patch soon.

Regards,

Vincenzo