notifier: Add blocking/atomic_notifier_chain_register_unique_prio()

Add variant of blocking/atomic_notifier_chain_register() functions that allow registration of a notifier only if it has unique priority, otherwise -EBUSY error code is returned by the new functions. Reviewed-by: Michał Mirosław <[email protected]> Signed-off-by: Dmitry Osipenko <[email protected]> Signed-off-by: Rafael J. Wysocki <[email protected]>
torvalds · May 19, 2022 · c82f898 · c82f898
1 parent 13dfd97
commit c82f898
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Showing 2 changed files with 74 additions and 19 deletions.
diff --git a/include/linux/notifier.h b/include/linux/notifier.h
@@ -150,6 +150,11 @@ extern int raw_notifier_chain_register(struct raw_notifier_head *nh,
 extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
  struct notifier_block *nb);
 
+extern int atomic_notifier_chain_register_unique_prio(
+ struct atomic_notifier_head *nh, struct notifier_block *nb);
+extern int blocking_notifier_chain_register_unique_prio(
+ struct blocking_notifier_head *nh, struct notifier_block *nb);
+
 extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
  struct notifier_block *nb);
 extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,

diff --git a/kernel/notifier.c b/kernel/notifier.c
@@ -20,7 +20,8 @@ BLOCKING_NOTIFIER_HEAD(reboot_notifier_list);
  */
 
 static int notifier_chain_register(struct notifier_block **nl,
- struct notifier_block *n)
+ struct notifier_block *n,
+ bool unique_priority)
 {
  while ((*nl) != NULL) {
  if (unlikely((*nl) == n)) {
@@ -30,6 +31,8 @@ static int notifier_chain_register(struct notifier_block **nl,
  }
  if (n->priority > (*nl)->priority)
  break;
+ if (n->priority == (*nl)->priority && unique_priority)
+ return -EBUSY;
  nl = &((*nl)->next);
  }
  n->next = *nl;
@@ -144,12 +147,35 @@ int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
  int ret;
 
  spin_lock_irqsave(&nh->lock, flags);
- ret = notifier_chain_register(&nh->head, n);
+ ret = notifier_chain_register(&nh->head, n, false);
  spin_unlock_irqrestore(&nh->lock, flags);
  return ret;
 }
 EXPORT_SYMBOL_GPL(atomic_notifier_chain_register);
 
+/**
+ * atomic_notifier_chain_register_unique_prio - Add notifier to an atomic notifier chain
+ * @nh: Pointer to head of the atomic notifier chain
+ * @n: New entry in notifier chain
+ *
+ * Adds a notifier to an atomic notifier chain if there is no other
+ * notifier registered using the same priority.
+ *
+ * Returns 0 on success, %-EEXIST or %-EBUSY on error.
+ */
+int atomic_notifier_chain_register_unique_prio(struct atomic_notifier_head *nh,
+ struct notifier_block *n)
+{
+ unsigned long flags;
+ int ret;
+
+ spin_lock_irqsave(&nh->lock, flags);
+ ret = notifier_chain_register(&nh->head, n, true);
+ spin_unlock_irqrestore(&nh->lock, flags);
+ return ret;
+}
+EXPORT_SYMBOL_GPL(atomic_notifier_chain_register_unique_prio);
+
 /**
  * atomic_notifier_chain_unregister - Remove notifier from an atomic notifier chain
  * @nh: Pointer to head of the atomic notifier chain
@@ -222,18 +248,9 @@ bool atomic_notifier_call_chain_is_empty(struct atomic_notifier_head *nh)
  * synchronized by an rwsem.
  */
 
-/**
- * blocking_notifier_chain_register - Add notifier to a blocking notifier chain
- * @nh: Pointer to head of the blocking notifier chain
- * @n: New entry in notifier chain
- *
- * Adds a notifier to a blocking notifier chain.
- * Must be called in process context.
- *
- * Returns 0 on success, %-EEXIST on error.
- */
-int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
- struct notifier_block *n)
+static int __blocking_notifier_chain_register(struct blocking_notifier_head *nh,
+ struct notifier_block *n,
+ bool unique_priority)
 {
  int ret;
 
@@ -243,15 +260,48 @@ int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
  * such times we must not call down_write().
  */
  if (unlikely(system_state == SYSTEM_BOOTING))
- return notifier_chain_register(&nh->head, n);
+ return notifier_chain_register(&nh->head, n, unique_priority);
 
  down_write(&nh->rwsem);
- ret = notifier_chain_register(&nh->head, n);
+ ret = notifier_chain_register(&nh->head, n, unique_priority);
  up_write(&nh->rwsem);
  return ret;
 }
+
+/**
+ * blocking_notifier_chain_register - Add notifier to a blocking notifier chain
+ * @nh: Pointer to head of the blocking notifier chain
+ * @n: New entry in notifier chain
+ *
+ * Adds a notifier to a blocking notifier chain.
+ * Must be called in process context.
+ *
+ * Returns 0 on success, %-EEXIST on error.
+ */
+int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
+ struct notifier_block *n)
+{
+ return __blocking_notifier_chain_register(nh, n, false);
+}
 EXPORT_SYMBOL_GPL(blocking_notifier_chain_register);
 
+/**
+ * blocking_notifier_chain_register_unique_prio - Add notifier to a blocking notifier chain
+ * @nh: Pointer to head of the blocking notifier chain
+ * @n: New entry in notifier chain
+ *
+ * Adds a notifier to an blocking notifier chain if there is no other
+ * notifier registered using the same priority.
+ *
+ * Returns 0 on success, %-EEXIST or %-EBUSY on error.
+ */
+int blocking_notifier_chain_register_unique_prio(struct blocking_notifier_head *nh,
+ struct notifier_block *n)
+{
+ return __blocking_notifier_chain_register(nh, n, true);
+}
+EXPORT_SYMBOL_GPL(blocking_notifier_chain_register_unique_prio);
+
 /**
  * blocking_notifier_chain_unregister - Remove notifier from a blocking notifier chain
  * @nh: Pointer to head of the blocking notifier chain
@@ -354,7 +404,7 @@ EXPORT_SYMBOL_GPL(blocking_notifier_call_chain);
 int raw_notifier_chain_register(struct raw_notifier_head *nh,
  struct notifier_block *n)
 {
- return notifier_chain_register(&nh->head, n);
+ return notifier_chain_register(&nh->head, n, false);
 }
 EXPORT_SYMBOL_GPL(raw_notifier_chain_register);
 
@@ -433,10 +483,10 @@ int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
  * such times we must not call mutex_lock().
  */
  if (unlikely(system_state == SYSTEM_BOOTING))
- return notifier_chain_register(&nh->head, n);
+ return notifier_chain_register(&nh->head, n, false);
 
  mutex_lock(&nh->mutex);
- ret = notifier_chain_register(&nh->head, n);
+ ret = notifier_chain_register(&nh->head, n, false);
  mutex_unlock(&nh->mutex);
  return ret;
 }