On Tue, May 10, 2022 at 1:33 AM Dmitry Osipenko
<dmitry.osipenko@xxxxxxxxxxxxx> wrote:
>
> Add atomic_notifier_call_chain_is_empty() that returns true if given
> atomic call chain is empty.
It would be good to mention a use case for it.
> Reviewed-by: Michał Mirosław <mirq-linux@xxxxxxxxxxxx>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
> ---
> 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
>
