Hello Waiman, Marek
Thanks for the review.
I've never used lockdep for debug but it seems preferable to
keep that feature working. It could be look like this:
diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index f7611c092db7..574f6de6084d 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 +117,31 @@ do { \
#ifdef CONFIG_DEBUG_MUTEXES
+int debug_devm_mutex_init(struct device *dev, struct mutex *lock);
+
+#define devm_mutex_init(dev, mutex) \
+({ \
+ int ret; \
+ mutex_init(mutex); \
+ ret = debug_devm_mutex_init(dev, mutex); \
+ ret; \
+})
+
void mutex_destroy(struct mutex *lock);
#else
+/*
+* When CONFIG_DEBUG_MUTEXES is off mutex_destroy is just a nop so
+* there's no really need to register it in devm subsystem.
+*/
+#define devm_mutex_init(dev, mutex) \
+({ \
+ typecheck(struct device *, dev); \
+ mutex_init(mutex); \
+ 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..967a5367c79a 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"
@@ -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 debug_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
And now I would drop the the refactoring patch with moving down
mutex_destroy. devm block is big enough to be declared standalone.
On 3/7/24 19:44, Marek Behún wrote:
On Thu, 7 Mar 2024 08:39:46 -0500
Waiman Long <longman@xxxxxxxxxx> wrote:
On 3/7/24 04:56, Marek Behún wrote:
On Thu, Mar 07, 2024 at 05:40:26AM +0300, George Stark 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()
Signed-off-by: George Stark <gnstark@xxxxxxxxxxxxxxxxx>
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
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);
Hi George,
look at
https://lore.kernel.org/lkml/7013bf9e-2663-4613-ae61-61872e81355b@xxxxxxxxxx/
where Matthew and Hans explain that devm_mutex_init needs to be a macro
because of the static lockdep key.
so this should be something like:
static inline int __devm_mutex_init(struct device *dev, struct mutex *mutex,
const char *name,
struct lock_class_key *key)
{
__mutex_init(mutex, name, key);
return devm_add_action_or_reset(dev, devm_mutex_release, mutex);
}
#define devm_mutex_init(dev, mutex) \
do { \
static struct lock_class_key __key; \
\
__devm_mutex_init(dev, (mutex), #mutex, &__key); \
} while (0);
Marek
Making devm_mutex_init() a function will make all the devm_mutex share
the same lockdep key. Making it a macro will make each caller of
devm_mutex_init() have a distinct lockdep key. It all depends on whether
all the devm_mutexes have the same lock usage pattern or not and whether
it is possible for one devm_mutex to be nested inside another. So either
way can be fine depending on the mutex usage pattern. My suggestion is
to use a function, if possible, unless it will cause a false positive
lockdep splat as there is a limit on the maximum # of lockdep keys that
can be used.
devm_mutex_init() should behave like other similar function
initializing stuff with resource management. I.e. it should behave like
mutex_init(), but with resource management.
mutex_init() is a macro generating static lockdep key for each instance,
so devm_mutex_init() should also generate static lockdep key for each
instance.
Marek
--
Best regards
George
