[PATCH v4 03/25] notifier: Add atomic/blocking_notifier_has_unique_priority()

Dmitry Osipenko
2021-11-26T18:22:43Z

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

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---
include/linux/notifier.h | 5 +++
kernel/notifier.c | 69 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 74 insertions(+)

diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index 924c9d7c8e73..2c4036f225e1 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_is_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 b20cb7b9b1f0..7a325b742104 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -122,6 +122,19 @@ static int notifier_call_chain_robust(struct notifier_block **nl,
return ret;
}

+static int notifier_has_unique_priority(struct notifier_block **nl,
+ struct notifier_block *n)
+{
+ while (*nl && (*nl)->priority >= n->priority) {
+ if ((*nl)->priority == n->priority && *nl != n)
+ return false;
+
+ nl = &((*nl)->next);
+ }
+
+ return true;
+}
+
/*
* Atomic notifier chain routines. Registration and unregistration
* use a spinlock, and call_chain is synchronized by RCU (no locks).
@@ -203,6 +216,30 @@ 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)
+{
+ unsigned long flags;
+ bool ret;
+
+ spin_lock_irqsave(&nh->lock, flags);
+ ret = notifier_has_unique_priority(&nh->head, n);
+ 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 +373,38 @@ bool blocking_notifier_call_chain_is_empty(struct blocking_notifier_head *nh)
}
EXPORT_SYMBOL_GPL(blocking_notifier_call_chain_is_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)
+{
+ bool ret;
+
+ /*
+ * 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_read().
+ */
+ if (system_state != SYSTEM_BOOTING)
+ down_read(&nh->rwsem);
+
+ ret = notifier_has_unique_priority(&nh->head, n);
+
+ if (system_state != SYSTEM_BOOTING)
+ up_read(&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