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

Dmitry Osipenko
2021-10-27T21:18:11Z

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 | 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