diff mbox series

[v4,02/25] notifier: Add blocking_notifier_call_chain_is_empty()

Message ID 20211126180101.27818-3-digetx@gmail.com (mailing list archive)
State New, archived
Headers show
Series Introduce power-off+restart call chain API | expand

Commit Message

Dmitry Osipenko Nov. 26, 2021, 6 p.m. UTC
Add blocking_notifier_call_chain_is_empty() that returns true if call
chain is empty.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---
 include/linux/notifier.h |  2 ++
 kernel/notifier.c        | 14 ++++++++++++++
 2 files changed, 16 insertions(+)

Comments

Rafael J. Wysocki Dec. 10, 2021, 6:14 p.m. UTC | #1
On Fri, Nov 26, 2021 at 7:01 PM Dmitry Osipenko <digetx@gmail.com> wrote:
>
> Add blocking_notifier_call_chain_is_empty() that returns true if call
> chain is empty.
>
> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
> ---
>  include/linux/notifier.h |  2 ++
>  kernel/notifier.c        | 14 ++++++++++++++
>  2 files changed, 16 insertions(+)
>
> diff --git a/include/linux/notifier.h b/include/linux/notifier.h
> index 4b80a815b666..924c9d7c8e73 100644
> --- a/include/linux/notifier.h
> +++ b/include/linux/notifier.h
> @@ -173,6 +173,8 @@ int blocking_notifier_call_chain_robust(struct blocking_notifier_head *nh,
>  int raw_notifier_call_chain_robust(struct raw_notifier_head *nh,
>                 unsigned long val_up, unsigned long val_down, void *v);
>
> +bool blocking_notifier_call_chain_is_empty(struct blocking_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 b8251dc0bc0f..b20cb7b9b1f0 100644
> --- a/kernel/notifier.c
> +++ b/kernel/notifier.c
> @@ -322,6 +322,20 @@ int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
>  }
>  EXPORT_SYMBOL_GPL(blocking_notifier_call_chain);
>
> +/**
> + *     blocking_notifier_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 blocking_notifier_call_chain_is_empty(struct blocking_notifier_head *nh)
> +{
> +       return !rcu_access_pointer(nh->head);
> +}
> +EXPORT_SYMBOL_GPL(blocking_notifier_call_chain_is_empty);

The check is not reliable (racy) without locking, so I wouldn't export
anything like this to modules.

At least IMO it should be added along with a user.
Dmitry Osipenko Dec. 10, 2021, 6:19 p.m. UTC | #2
10.12.2021 21:14, Rafael J. Wysocki пишет:
> On Fri, Nov 26, 2021 at 7:01 PM Dmitry Osipenko <digetx@gmail.com> wrote:
>>
>> Add blocking_notifier_call_chain_is_empty() that returns true if call
>> chain is empty.
>>
>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
>> ---
>>  include/linux/notifier.h |  2 ++
>>  kernel/notifier.c        | 14 ++++++++++++++
>>  2 files changed, 16 insertions(+)
>>
>> diff --git a/include/linux/notifier.h b/include/linux/notifier.h
>> index 4b80a815b666..924c9d7c8e73 100644
>> --- a/include/linux/notifier.h
>> +++ b/include/linux/notifier.h
>> @@ -173,6 +173,8 @@ int blocking_notifier_call_chain_robust(struct blocking_notifier_head *nh,
>>  int raw_notifier_call_chain_robust(struct raw_notifier_head *nh,
>>                 unsigned long val_up, unsigned long val_down, void *v);
>>
>> +bool blocking_notifier_call_chain_is_empty(struct blocking_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 b8251dc0bc0f..b20cb7b9b1f0 100644
>> --- a/kernel/notifier.c
>> +++ b/kernel/notifier.c
>> @@ -322,6 +322,20 @@ int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
>>  }
>>  EXPORT_SYMBOL_GPL(blocking_notifier_call_chain);
>>
>> +/**
>> + *     blocking_notifier_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 blocking_notifier_call_chain_is_empty(struct blocking_notifier_head *nh)
>> +{
>> +       return !rcu_access_pointer(nh->head);
>> +}
>> +EXPORT_SYMBOL_GPL(blocking_notifier_call_chain_is_empty);
> 
> The check is not reliable (racy) without locking, so I wouldn't export
> anything like this to modules.
> 
> At least IMO it should be added along with a user.
> 

I'll remove the export since it's indeed not obvious how other users may
want to use this function.
diff mbox series

Patch

diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index 4b80a815b666..924c9d7c8e73 100644
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -173,6 +173,8 @@  int blocking_notifier_call_chain_robust(struct blocking_notifier_head *nh,
 int raw_notifier_call_chain_robust(struct raw_notifier_head *nh,
 		unsigned long val_up, unsigned long val_down, void *v);
 
+bool blocking_notifier_call_chain_is_empty(struct blocking_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 b8251dc0bc0f..b20cb7b9b1f0 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -322,6 +322,20 @@  int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
 }
 EXPORT_SYMBOL_GPL(blocking_notifier_call_chain);
 
+/**
+ *	blocking_notifier_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 blocking_notifier_call_chain_is_empty(struct blocking_notifier_head *nh)
+{
+	return !rcu_access_pointer(nh->head);
+}
+EXPORT_SYMBOL_GPL(blocking_notifier_call_chain_is_empty);
+
 /*
  *	Raw notifier chain routines.  There is no protection;
  *	the caller must provide it.  Use at your own risk!