On Thu, 5 Apr 2018, Petr Mladek wrote:
> The existing API allows to pass a sample data to initialize the shadow
> data. It works well when the data are position independent. But it fails
> miserably when we need to set a pointer to the shadow structure itself.
> Unfortunately, we might need to initialize the pointer surprisingly
> often because of struct list_head. It is even worse because the list
> might be hidden in other common structures, for example, struct mutex,
> struct wait_queue_head.
> For example, this was needed to fix races in ALSA sequncer. It required
> to add mutex into struct snd_seq_client. See commit b3defb791b26ea06
> ("ALSA: seq: Make ioctls race-free") and commit d15d662e89fc667b9
> ("ALSA: seq: Fix racy pool initializations")
> This patch makes the API more safe. A custom constructor function and data
> are passed to klp_shadow_*alloc() functions instead of the sample data.
> Note that ctor_data are not longer a template for shadow->data. It might
s/not longer/no longer/
> point to any data that might be necessary when the constructor is called.