[PATCH v5 02/10] locking/mutex: introduce devm_mutex_init

[George Stark <gnstark@salutedevices.com>]

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@salutedevices.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 Hello Christophe. Hope you don't mind I put you SoB tag because you helped alot
 to make this patch happen.

 include/linux/mutex.h        | 13 +++++++++++++
 kernel/locking/mutex-debug.c | 22 ++++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index f7611c092db7..9bcf72cb941a 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -22,6 +22,8 @@
 #include <linux/cleanup.h>
 #include <linux/mutex_types.h>

+struct device;
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 # define __DEP_MAP_MUTEX_INITIALIZER(lockname)			\
 		, .dep_map = {					\
@@ -115,10 +117,21 @@ do {							\

 #ifdef CONFIG_DEBUG_MUTEXES

+int devm_mutex_init(struct device *dev, struct mutex *lock);
 void mutex_destroy(struct mutex *lock);

 #else

+static inline int devm_mutex_init(struct device *dev, struct mutex *lock)
+{
+	/*
+	 * since mutex_destroy is nop actually there's no need to register it
+	 * in devm subsystem.
+	 */
+	mutex_init(lock);
+	return 0;
+}
+
 static inline void mutex_destroy(struct mutex *lock) {}

 #endif
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