[RFC PATCH 1/1] locking: introduce devm_mutex_init and devm_mutex_destroy

[George Stark]

Using of devm API leads to certain order of releasing resources.
So all dependent resources which are not devm-wrapped should be deleted
with respect to devm-release order. Mutex is one of such objects that
often is bound to other resources and has no own devm wrapping.
Since mutex_destroy() actually does nothing in non-debug builds
frequently calling mutex_destroy() is just ignored which is safe for now
but wrong formally and can lead to a problem if mutex_destroy() will be
extended so introduce devm_mutex_init() and devm_mutex_destroy().

Signed-off-by: George Stark <gnstark@xxxxxxxxxxxxxxxxx>
---
 include/linux/mutex.h  |  3 +++
 kernel/locking/mutex.c | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index a33aa9eb9fc3..7f60cd842322 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -119,6 +119,9 @@ do {									\
 extern void __mutex_init(struct mutex *lock, const char *name,
 			 struct lock_class_key *key);
 
+int devm_mutex_init(struct device *dev, struct mutex *lock);
+void devm_mutex_destroy(struct device *dev, struct mutex *lock);
+
 /**
  * mutex_is_locked - is the mutex locked
  * @lock: the mutex to be queried
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index d973fe6041bf..a73124719dcb 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -56,6 +56,43 @@ __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
 }
 EXPORT_SYMBOL(__mutex_init);
 
+static void devm_mutex_release(struct device *dev, void *res)
+{
+	mutex_destroy(*(struct mutex **)res);
+}
+
+static int devm_mutex_match(struct device *dev, void *res, void *data)
+{
+	struct mutex **r = res;
+
+	if (WARN_ON(!r || !*r))
+		return 0;
+
+	return *r == data;
+}
+
+int devm_mutex_init(struct device *dev, struct mutex *lock)
+{
+	struct mutex **ptr;
+
+	ptr = devres_alloc(devm_mutex_release, sizeof(*ptr), GFP_KERNEL);
+	if (!ptr)
+		return -ENOMEM;
+
+	mutex_init(lock);
+
+	*ptr = lock;
+	devres_add(dev, ptr);
+	return 0;
+}
+EXPORT_SYMBOL(devm_mutex_init);
+
+void devm_mutex_destroy(struct device *dev, struct mutex *lock)
+{
+	devres_release(dev, devm_mutex_release, devm_mutex_match, lock);
+}
+EXPORT_SYMBOL(devm_mutex_destroy);
+
 /*
  * @owner: contains: 'struct task_struct *' to the current lock owner,
  * NULL means not owned. Since task_struct pointers are aligned at
-- 
2.38.4