Hi,

On 12/14/23 11:06, Christophe Leroy wrote:

Le 13/12/2023 à 23:30, George Stark a écrit :

quoted

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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 wrapper.
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() is
extended so introduce devm_mutex_init().

So you abandonned the idea of using mutex.h ?

I can't see the point to spread mutex functions into devm-helpers.h

Adding a mutex_destroy macro for this purpose looks odd. And if someone 
defines a new version of mutex_destroy() and forget the macro, it will 
go undetected.

Usually macros of that type serve the purpose of defining a fallback 
when the macro is not defined. In that case, when someone adds a new 
version without defining the macro, it gets detected because if 
conflicts with the fallback.
But in your case it works the other way round, so I will just go undetected.

For me the best solution remains to use mutex.h and have 
devm_mutex_init() defined or declared at the same place as mutex_destroy().

FWIW defining devm_mutex_init() in mutex.h is fine
with me and makes sense to me. I also agree that putting
it there would be better if that is acceptable for
the mutex maintainers.

devm-helpers.h is there for helpers which don't fit
in another place.

Regards,

Hans

quoted

Signed-off-by: George Stark <redacted>
---
  include/linux/devm-helpers.h | 27 +++++++++++++++++++++++++++
  1 file changed, 27 insertions(+)

diff --git a/include/linux/devm-helpers.h b/include/linux/devm-helpers.h
index 74891802200d..4043c3481d2e 100644
--- a/include/linux/devm-helpers.h
+++ b/include/linux/devm-helpers.h

@@ -24,6 +24,7 @@
   */

  #include <linux/device.h>
+#include <linux/mutex.h>
  #include <linux/workqueue.h>

  static inline void devm_delayed_work_drop(void *res)

@@ -76,4 +77,30 @@ static inline int devm_work_autocancel(struct device *dev,
         return devm_add_action(dev, devm_work_drop, w);
  }

+#ifdef mutex_destroy
+static inline void devm_mutex_release(void *res)
+{
+       mutex_destroy(res);
+}
+#endif
+
+/**
+ * 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.
+ */
+static inline int devm_mutex_init(struct device *dev, struct mutex *lock)
+{
+       mutex_init(lock);
+#ifdef mutex_destroy
+       return devm_add_action_or_reset(dev, devm_mutex_release, lock);
+#else
+       return 0;
+#endif
+}
+
  #endif
--

2.25.1