RE: [PATCH v3 0/3] kernel/notifier.c: avoid duplicate registration

[Nixiaoming]

On Wed, July 10, 2019 1:56 PM Greg KH wrote:
>On Wed, Jul 10, 2019 at 11:09:07AM +0800, Xiaoming Ni wrote:
>> Registering the same notifier to a hook repeatedly can cause the hook
>> list to form a ring or lose other members of the list.
>
>Then don't do that :)
>

Duplicate registration is checked and exited in notifier_chain_cond_register()

Duplicate registration was checked in notifier_chain_register() but only 
the alarm was triggered without exiting. added by commit 831246570d34692e 
("kernel/notifier.c: double register detection")

This patch is similar to commit 8312465 and notifier_chain_cond_register(),
 with actual prevention for such behaviour,  which I think is necessary to 
 avoid the formation of a linked list ring.

>Is there any in-kernel users that do do this?  If so, please just fix
>them.
>
Notifier_chain_register() is not a hotspot path.
Adding a check here can make the kernel more stable.

Thanks

Xiaoming Ni


>thanks,
>
>greg k-h
>