[PATCH v8 01/27] notifier: Add atomic_notifier_call_chain_is_empty()

Dmitry Osipenko
2022-05-09T23:32:09Z

Add atomic_notifier_call_chain_is_empty() that returns true if given
atomic call chain is empty.

Reviewed-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
include/linux/notifier.h | 2 ++
kernel/notifier.c | 13 +++++++++++++
2 files changed, 15 insertions(+)

diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index 87069b8459af..95e2440037de 100644
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -173,6 +173,8 @@ extern int blocking_notifier_call_chain_robust(struct blocking_notifier_head *nh
extern int raw_notifier_call_chain_robust(struct raw_notifier_head *nh,
unsigned long val_up, unsigned long val_down, void *v);

+extern bool atomic_notifier_call_chain_is_empty(struct atomic_notifier_head *nh);
+
#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 ba005ebf4730..aaf5b56452a6 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -204,6 +204,19 @@ int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
EXPORT_SYMBOL_GPL(atomic_notifier_call_chain);
NOKPROBE_SYMBOL(atomic_notifier_call_chain);

+/**
+ * atomicnotifier_call_chain_is_empty - Check whether notifier chain is empty
+ * @nh: Pointer to head of the blocking notifier chain
+ *
+ * Checks whether notifier chain is empty.
+ *
+ * Returns true is notifier chain is empty, false otherwise.
+ */
+bool atomic_notifier_call_chain_is_empty(struct atomic_notifier_head *nh)
+{
+ return !rcu_access_pointer(nh->head);
+}
+
/*
* Blocking notifier chain routines. All access to the chain is
* synchronized by an rwsem.
--
2.35.1