[PATCH v4 02/10] locking: introduce devm_mutex_init

[George Stark]

Using of devm API leads to a 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()

Signed-off-by: George Stark <gnstark at salutedevices.com>
---
 include/linux/mutex.h        | 23 +++++++++++++++++++++++
 kernel/locking/mutex-debug.c | 22 ++++++++++++++++++++++
 2 files changed, 45 insertions(+)

diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index a33aa9eb9fc3..ebd03ff1ef66 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -21,6 +21,8 @@
 #include <linux/debug_locks.h>
 #include <linux/cleanup.h>
 
+struct device;
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 # define __DEP_MAP_MUTEX_INITIALIZER(lockname)			\
 		, .dep_map = {					\
@@ -127,6 +129,20 @@ extern void __mutex_init(struct mutex *lock, const char *name,
  */
 extern bool mutex_is_locked(struct mutex *lock);
 
+#ifdef CONFIG_DEBUG_MUTEXES
+
+int devm_mutex_init(struct device *dev, struct mutex *lock);
+
+#else
+
+static inline int devm_mutex_init(struct device *dev, struct mutex *lock)
+{
+	mutex_init(lock);
+	return 0;
+}
+
+#endif
+
 #else /* !CONFIG_PREEMPT_RT */
 /*
  * Preempt-RT variant based on rtmutexes.
@@ -169,6 +185,13 @@ do {							\
 							\
 	__mutex_init((mutex), #mutex, &__key);		\
 } while (0)
+
+static inline int devm_mutex_init(struct device *dev, struct mutex *lock)
+{
+	mutex_init(lock);
+	return 0;
+}
+
 #endif /* CONFIG_PREEMPT_RT */
 
 /*
diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
index bc8abb8549d2..c9efab1a8026 100644
--- a/kernel/locking/mutex-debug.c
+++ b/kernel/locking/mutex-debug.c
@@ -19,6 +19,7 @@
 #include <linux/kallsyms.h>
 #include <linux/interrupt.h>
 #include <linux/debug_locks.h>
+#include <linux/device.h>
 
 #include "mutex.h"
 
@@ -104,3 +105,24 @@ void mutex_destroy(struct mutex *lock)
 }
 
 EXPORT_SYMBOL_GPL(mutex_destroy);
+
+static void devm_mutex_release(void *res)
+{
+	mutex_destroy(res);
+}
+
+/**
+ * devm_mutex_init - Resource-managed mutex initialization
+ * @dev:	Device which lifetime mutex is bound to
+ * @lock:	Pointer to a mutex
+ *
+ * Initialize mutex which is automatically destroyed when the driver is detached.
+ *
+ * Returns: 0 on success or a negative error code on failure.
+ */
+int devm_mutex_init(struct device *dev, struct mutex *lock)
+{
+	mutex_init(lock);
+	return devm_add_action_or_reset(dev, devm_mutex_release, lock);
+}
+EXPORT_SYMBOL_GPL(devm_mutex_init);
-- 
2.25.1