[PATCH 5.15.y 1/2] of: Add cleanup.h based auto release via __free(device_node) markings

[PATCH 5.15.y 1/2] of: Add cleanup.h based auto release via __free(device_node) markings

[Bin Lan]

From: Jonathan Cameron <Jonathan.Cameron@huawei.com>

[ Upstream commit 9448e55d032d99af8e23487f51a542d51b2f1a48 ]

The recent addition of scope based cleanup support to the kernel
provides a convenient tool to reduce the chances of leaking reference
counts where of_node_put() should have been called in an error path.

This enables
	struct device_node *child __free(device_node) = NULL;

	for_each_child_of_node(np, child) {
		if (test)
			return test;
	}

with no need for a manual call of of_node_put().
A following patch will reduce the scope of the child variable to the
for loop, to avoid an issues with ordering of autocleanup, and make it
obvious when this assigned a non NULL value.

In this simple example the gains are small but there are some very
complex error handling cases buried in these loops that will be
greatly simplified by enabling early returns with out the need
for this manual of_node_put() call.

Note that there are coccinelle checks in
scripts/coccinelle/iterators/for_each_child.cocci to detect a failure
to call of_node_put(). This new approach does not cause false positives.
Longer term we may want to add scripting to check this new approach is
done correctly with no double of_node_put() calls being introduced due
to the auto cleanup. It may also be useful to script finding places
this new approach is useful.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20240225142714.286440-2-jic23@kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bin Lan <lanbincn@139.com>
---
 include/linux/of.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/of.h b/include/linux/of.h
index 29f657101f4f..3c840c487995 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -13,6 +13,7 @@
  */
 #include <linux/types.h>
 #include <linux/bitops.h>
+#include <linux/cleanup.h>
 #include <linux/errno.h>
 #include <linux/kobject.h>
 #include <linux/mod_devicetable.h>
@@ -128,6 +129,7 @@ static inline struct device_node *of_node_get(struct device_node *node)
 }
 static inline void of_node_put(struct device_node *node) { }
 #endif /* !CONFIG_OF_DYNAMIC */
+DEFINE_FREE(device_node, struct device_node *, if (_T) of_node_put(_T))
 
 /* Pointer for first entry in chain of all nodes. */
 extern struct device_node *of_root;
-- 
2.43.0

[PATCH 5.15.y 2/2] cpufreq: Avoid a bad reference count on CPU node

[Bin Lan]

From: Miquel Sabaté Solà <mikisabate@gmail.com>

[ Upstream commit c0f02536fffbbec71aced36d52a765f8c4493dc2 ]

In the parse_perf_domain function, if the call to
of_parse_phandle_with_args returns an error, then the reference to the
CPU device node that was acquired at the start of the function would not
be properly decremented.

Address this by declaring the variable with the __free(device_node)
cleanup attribute.

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://patch.msgid.link/20240917134246.584026-1-mikisabate@gmail.com
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
[ Minor context conflict resolved. ]
Signed-off-by: Bin Lan <lanbincn@139.com>
---
 include/linux/cpufreq.h | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 8e3a1d4e0a3a..6ed4c82af367 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -1014,11 +1014,10 @@ static inline int cpufreq_table_count_valid_entries(const struct cpufreq_policy
 static inline int parse_perf_domain(int cpu, const char *list_name,
 				    const char *cell_name)
 {
-	struct device_node *cpu_np;
 	struct of_phandle_args args;
 	int ret;
 
-	cpu_np = of_cpu_device_node_get(cpu);
+	struct device_node *cpu_np __free(device_node) = of_cpu_device_node_get(cpu);
 	if (!cpu_np)
 		return -ENODEV;
 
@@ -1027,8 +1026,6 @@ static inline int parse_perf_domain(int cpu, const char *list_name,
 	if (ret < 0)
 		return ret;
 
-	of_node_put(cpu_np);
-
 	return args.args[0];
 }
 
-- 
2.43.0