[PATCH v2 1/2] devres: add devm_remove_action_nowarn()

[Danilo Krummrich <dakr@kernel.org>]

devm_remove_action() warns if the action to remove does not exist
(anymore).

The Rust devres abstraction, however, has a use-case to call
devm_remove_action() at a point where it can't be guaranteed that the
corresponding action hasn't been released yet.

In particular, an instance of `Devres<T>` may be dropped after the
action has been released. So far, `Devres<T>` worked around this by
keeping the inner type alive.

Hence, add devm_remove_action_nowarn(), which returns an error code if
the action has been removed already.

A subsequent patch uses devm_remove_action_nowarn() to remove the action
when `Devres<T>` is dropped.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
v2: clarify area of use of devm_remove_action_nowarn()
---
 drivers/base/devres.c  | 23 ++++++++++++++++++-----
 include/linux/device.h | 18 +++++++++++++++++-
 2 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/drivers/base/devres.c b/drivers/base/devres.c
index 2152eec0c135..93e7779ef21e 100644
--- a/drivers/base/devres.c
+++ b/drivers/base/devres.c
@@ -750,25 +750,38 @@ int __devm_add_action(struct device *dev, void (*action)(void *), void *data, co
 EXPORT_SYMBOL_GPL(__devm_add_action);
 
 /**
- * devm_remove_action() - removes previously added custom action
+ * devm_remove_action_nowarn() - removes previously added custom action
  * @dev: Device that owns the action
  * @action: Function implementing the action
  * @data: Pointer to data passed to @action implementation
  *
  * Removes instance of @action previously added by devm_add_action().
  * Both action and data should match one of the existing entries.
+ *
+ * In contrast to devm_remove_action(), this function does not WARN() if no
+ * entry could have been found.
+ *
+ * This should only be used if the action is contained in an object with
+ * independent lifetime management, e.g. the Devres rust abstraction.
+ *
+ * Causing the warning from regular driver code most likely indicates an abuse
+ * of the devres API.
+ *
+ * Returns: 0 on success, -ENOENT if no entry could have been found.
  */
-void devm_remove_action(struct device *dev, void (*action)(void *), void *data)
+int devm_remove_action_nowarn(struct device *dev,
+			      void (*action)(void *),
+			      void *data)
 {
 	struct action_devres devres = {
 		.data = data,
 		.action = action,
 	};
 
-	WARN_ON(devres_destroy(dev, devm_action_release, devm_action_match,
-			       &devres));
+	return devres_destroy(dev, devm_action_release, devm_action_match,
+			      &devres);
 }
-EXPORT_SYMBOL_GPL(devm_remove_action);
+EXPORT_SYMBOL_GPL(devm_remove_action_nowarn);
 
 /**
  * devm_release_action() - release previously added custom action
diff --git a/include/linux/device.h b/include/linux/device.h
index 667cb6db9019..6879d5e8ac3d 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -399,7 +399,23 @@ void __iomem *devm_of_iomap(struct device *dev,
 #endif
 
 /* allows to add/remove a custom action to devres stack */
-void devm_remove_action(struct device *dev, void (*action)(void *), void *data);
+int devm_remove_action_nowarn(struct device *dev, void (*action)(void *), void *data);
+
+/**
+ * devm_remove_action() - removes previously added custom action
+ * @dev: Device that owns the action
+ * @action: Function implementing the action
+ * @data: Pointer to data passed to @action implementation
+ *
+ * Removes instance of @action previously added by devm_add_action().
+ * Both action and data should match one of the existing entries.
+ */
+static inline
+void devm_remove_action(struct device *dev, void (*action)(void *), void *data)
+{
+	WARN_ON(devm_remove_action_nowarn(dev, action, data));
+}
+
 void devm_release_action(struct device *dev, void (*action)(void *), void *data);
 
 int __devm_add_action(struct device *dev, void (*action)(void *), void *data, const char *name);

base-commit: 06e843bbbf2107463249ea6f6b1a736f5647e24a
-- 
2.47.1