2024-03-14 20:19:37

by George Stark

Subject: [PATCH v7 1/8] locking/mutex: introduce devm_mutex_init()

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().

Suggested-by: Christophe Leroy <[email protected]>
Signed-off-by: George Stark <[email protected]>
Reviewed-by: Christophe Leroy <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Reviewed-by: Marek Behún <[email protected]>
Acked-by: Waiman Long <[email protected]>
---
include/linux/mutex.h | 27 +++++++++++++++++++++++++++
kernel/locking/mutex-debug.c | 11 +++++++++++
2 files changed, 38 insertions(+)

diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index 67edc4ca2bee..a561c629d89f 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 = { \
@@ -117,6 +119,31 @@ do { \
} while (0)
#endif /* CONFIG_PREEMPT_RT */

+#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)
+{
+ /*
+ * When CONFIG_DEBUG_MUTEXES is off mutex_destroy() is just a nop so
+ * no really need to register it in the devm subsystem.
+ */
+ return 0;
+}
+
+#endif
+
+#define devm_mutex_init(dev, mutex) \
+({ \
+ typeof(mutex) mutex_ = (mutex); \
+ \
+ mutex_init(mutex_); \
+ __devm_mutex_init(dev, mutex_); \
+})
+
/*
* See kernel/locking/mutex.c for detailed documentation of these APIs.
* Also see Documentation/locking/mutex-design.rst.
diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
index bc8abb8549d2..f7e848defd50 100644
--- a/kernel/locking/mutex-debug.c
+++ b/kernel/locking/mutex-debug.c
@@ -12,6 +12,7 @@
*/
#include <linux/mutex.h>
#include <linux/delay.h>
+#include <linux/device.h>
#include <linux/export.h>
#include <linux/poison.h>
#include <linux/sched.h>
@@ -89,6 +90,16 @@ void debug_mutex_init(struct mutex *lock, const char *name,
lock->magic = lock;
}

+static void devm_mutex_release(void *res)
+{
+ mutex_destroy(res);
+}
+
+int __devm_mutex_init(struct device *dev, struct mutex *lock)
+{
+ return devm_add_action_or_reset(dev, devm_mutex_release, lock);
+}
+
/***
* mutex_destroy - mark a mutex unusable
* @lock: the mutex to be destroyed
--
2.25.1

2024-03-14 23:37:47

by Andy Shevchenko

Subject: Re: [PATCH v7 1/8] locking/mutex: introduce devm_mutex_init()

On Thu, Mar 14, 2024 at 10:19 PM George Stark <[email protected]> wrote:
>
> 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().

..

> /***

Unrelated to your patch, but there are too many asterisks :-)

> * mutex_destroy - mark a mutex unusable
> * @lock: the mutex to be destroyed

--
With Best Regards,
Andy Shevchenko