Subject: [PATCH v2 03/45] notifier: Add atomic/blocking_notifier_has_unique_priority()

From: Dmitry Osipenko <[email-masked]>
Date: Thu, 28 Oct 2021 00:16:33 +0300

Add atomic/blocking_notifier_has_unique_priority() helpers which return
true if given handler has unique priority.

Signed-off-by: Dmitry Osipenko <[email-masked]>
---
 include/linux/notifier.h |  5 +++
 kernel/notifier.c        | 74 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 79 insertions(+)

diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index 054271e9cb20..b782ce100022 100644
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -175,6 +175,11 @@ int raw_notifier_call_chain_robust(struct raw_notifier_head *nh,
 
 bool blocking_notifier_call_chain_empty(struct blocking_notifier_head *nh);
 
+bool atomic_notifier_has_unique_priority(struct atomic_notifier_head *nh,
+		struct notifier_block *nb);
+bool blocking_notifier_has_unique_priority(struct blocking_notifier_head *nh,
+		struct notifier_block *nb);
+
 #define NOTIFY_DONE		0x0000		/* Don't care */
 #define NOTIFY_OK		0x0001		/* Suits me */
 #define NOTIFY_STOP_MASK	0x8000		/* Don't call further */
diff --git a/kernel/notifier.c b/kernel/notifier.c
index 1f7ba8988b90..cf0e1c4bd364 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -203,6 +203,40 @@ int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
 EXPORT_SYMBOL_GPL(atomic_notifier_call_chain);
 NOKPROBE_SYMBOL(atomic_notifier_call_chain);
 
+/**
+ *	atomic_notifier_has_unique_priority - Checks whether notifier's priority is unique
+ *	@nh: Pointer to head of the atomic notifier chain
+ *	@n: Entry in notifier chain to check
+ *
+ *	Checks whether there is another notifier in the chain with the same priority.
+ *	Must be called in process context.
+ *
+ *	Returns true if priority is unique, false otherwise.
+ */
+bool atomic_notifier_has_unique_priority(struct atomic_notifier_head *nh,
+		struct notifier_block *n)
+{
+	struct notifier_block **nl = &nh->head;
+	unsigned long flags;
+	bool ret = true;
+
+	spin_lock_irqsave(&nh->lock, flags);
+
+	while ((*nl) != NULL && (*nl)->priority >= n->priority) {
+		if ((*nl)->priority == n->priority && (*nl) != n) {
+			ret = false;
+			break;
+		}
+
+		nl = &((*nl)->next);
+	}
+
+	spin_unlock_irqrestore(&nh->lock, flags);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(atomic_notifier_has_unique_priority);
+
 /*
  *	Blocking notifier chain routines.  All access to the chain is
  *	synchronized by an rwsem.
@@ -336,6 +370,46 @@ bool blocking_notifier_call_chain_empty(struct blocking_notifier_head *nh)
 }
 EXPORT_SYMBOL_GPL(blocking_notifier_call_chain_empty);
 
+/**
+ *	blocking_notifier_has_unique_priority - Checks whether notifier's priority is unique
+ *	@nh: Pointer to head of the blocking notifier chain
+ *	@n: Entry in notifier chain to check
+ *
+ *	Checks whether there is another notifier in the chain with the same priority.
+ *	Must be called in process context.
+ *
+ *	Returns true if priority is unique, false otherwise.
+ */
+bool blocking_notifier_has_unique_priority(struct blocking_notifier_head *nh,
+		struct notifier_block *n)
+{
+	struct notifier_block **nl = &nh->head;
+	bool ret = true;
+
+	/*
+	 * This code gets used during boot-up, when task switching is
+	 * not yet working and interrupts must remain disabled.  At
+	 * such times we must not call down_write().
+	 */
+	if (system_state != SYSTEM_BOOTING)
+		down_write(&nh->rwsem);
+
+	while ((*nl) != NULL && (*nl)->priority >= n->priority) {
+		if ((*nl)->priority == n->priority && (*nl) != n) {
+			ret = false;
+			break;
+		}
+
+		nl = &((*nl)->next);
+	}
+
+	if (system_state != SYSTEM_BOOTING)
+		up_write(&nh->rwsem);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(blocking_notifier_has_unique_priority);
+
 /*
  *	Raw notifier chain routines.  There is no protection;
  *	the caller must provide it.  Use at your own risk!
-- 
2.33.1