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 >