[PATCH v3] drivers: cacheinfo: use __free attribute instead of of_node_put()

[Vincenzo Mezzela]

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().

To introduce this feature, some modifications to the code structure were
necessary. The original pattern:
```
prev = np;
while(...) {
  [...]
  np = of_find_next_cache_node(np);
  of_node_put(prev);
  prev = np;
  [...]
}
```
has been updated to:
```
while(...) {
  [...]
  struct device_node __free(device_node) *prev = np;
  np =  of_find_next_cache_node(np)
  [...]
}
```
With this change, the previous node is automatically cleaned up at the end
of each iteration, allowing the elimination of all of_node_put() calls and 
some goto statements.

Suggested-by: Julia Lawall <julia.lawall@xxxxxxxx>
Signed-off-by: Vincenzo Mezzela <vincenzo.mezzela@xxxxxxxxx>
---
This version is submitted as a regular patch after succesfully testing
the code to ensure that the cleanup function is called correctly at the
end of each iteration of the loop on the `prev` device node.
Testing was conducted on QEMU using KGDB, with modifications to force the
execution path to hit the changed code.

This work follows a previous patch [1] that introduced the same feature
in drivers/base/arch_topology.c .

- [1] https://lore.kernel.org/lkml/20240607163350.392971-1-vincenzo.mezzela@xxxxxxxxx/

changes from v1:
- Fixed coding style that was triggering checkpatch.pl
- Link to v1: https://lore.kernel.org/all/20240622152526.131974-2-vincenzo.mezzela@xxxxxxxxx/
changes from v2:
- More detailed changelog
- Link to v2: https://lore.kernel.org/all/20240702170241.104934-1-vincenzo.mezzela@xxxxxxxxx/

 drivers/base/cacheinfo.c | 41 +++++++++++++---------------------------
 1 file changed, 13 insertions(+), 28 deletions(-)

diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
index 23b8cba4a2a3..7a7609298e18 100644
--- a/drivers/base/cacheinfo.c
+++ b/drivers/base/cacheinfo.c
@@ -202,29 +202,24 @@ static void cache_of_set_props(struct cacheinfo *this_leaf,
 
 static int cache_setup_of_node(unsigned int cpu)
 {
-	struct device_node *np, *prev;
 	struct cacheinfo *this_leaf;
 	unsigned int index = 0;
 
-	np = of_cpu_device_node_get(cpu);
+	struct device_node *np __free(device_node) = of_cpu_device_node_get(cpu);
 	if (!np) {
 		pr_err("Failed to find cpu%d device node\n", cpu);
 		return -ENOENT;
 	}
 
 	if (!of_check_cache_nodes(np)) {
-		of_node_put(np);
 		return -ENOENT;
 	}
 
-	prev = np;
-
 	while (index < cache_leaves(cpu)) {
 		this_leaf = per_cpu_cacheinfo_idx(cpu, index);
 		if (this_leaf->level != 1) {
+			struct device_node *prev __free(device_node) = np;
 			np = of_find_next_cache_node(np);
-			of_node_put(prev);
-			prev = np;
 			if (!np)
 				break;
 		}
@@ -233,8 +228,6 @@ static int cache_setup_of_node(unsigned int cpu)
 		index++;
 	}
 
-	of_node_put(np);
-
 	if (index != cache_leaves(cpu)) /* not all OF nodes populated */
 		return -ENOENT;
 
@@ -243,17 +236,14 @@ static int cache_setup_of_node(unsigned int cpu)
 
 static bool of_check_cache_nodes(struct device_node *np)
 {
-	struct device_node *next;
-
 	if (of_property_present(np, "cache-size")   ||
 	    of_property_present(np, "i-cache-size") ||
 	    of_property_present(np, "d-cache-size") ||
 	    of_property_present(np, "cache-unified"))
 		return true;
 
-	next = of_find_next_cache_node(np);
+	struct device_node *next __free(device_node) = of_find_next_cache_node(np);
 	if (next) {
-		of_node_put(next);
 		return true;
 	}
 
@@ -287,12 +277,10 @@ static int of_count_cache_leaves(struct device_node *np)
 int init_of_cache_level(unsigned int cpu)
 {
 	struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);
-	struct device_node *np = of_cpu_device_node_get(cpu);
-	struct device_node *prev = NULL;
+	struct device_node *np __free(device_node) = of_cpu_device_node_get(cpu);
 	unsigned int levels = 0, leaves, level;
 
 	if (!of_check_cache_nodes(np)) {
-		of_node_put(np);
 		return -ENOENT;
 	}
 
@@ -300,30 +288,27 @@ int init_of_cache_level(unsigned int cpu)
 	if (leaves > 0)
 		levels = 1;
 
-	prev = np;
-	while ((np = of_find_next_cache_node(np))) {
-		of_node_put(prev);
-		prev = np;
+	while (1) {
+		struct device_node *prev __free(device_node) = np;
+		np = of_find_next_cache_node(np);
+		if (!np)
+			break;
+
 		if (!of_device_is_compatible(np, "cache"))
-			goto err_out;
+			return -EINVAL;
 		if (of_property_read_u32(np, "cache-level", &level))
-			goto err_out;
+			return -EINVAL;
 		if (level <= levels)
-			goto err_out;
+			return -EINVAL;
 
 		leaves += of_count_cache_leaves(np);
 		levels = level;
 	}
 
-	of_node_put(np);
 	this_cpu_ci->num_levels = levels;
 	this_cpu_ci->num_leaves = leaves;
 
 	return 0;
-
-err_out:
-	of_node_put(np);
-	return -EINVAL;
 }
 
 #else
-- 
2.43.0