Re: [Letux-kernel] BUG: drivers/pinctrl/core: races in pinctrl_groups and deferred probing

[H. Nikolaus Schaller]

Hi Tony,

> Am 18.06.2018 um 20:17 schrieb Tony Lindgren <tony@xxxxxxxxxxx>:
> 
> * H. Nikolaus Schaller <hns@xxxxxxxxxxxxx> [180618 16:46]:
> 
>> 
>> I can also demonstrate that the duplication has gone:
> 
> OK good to hear.
> 
>> And I was no longer able to reproduce the strcmp(NULL) issue. So it is either better hidden
>> or gone.
> 
> It should not be possible with checks preventing registering
> a group or function with no name. I'll try to repost the whole
> series tomorrow with that added.

Fine.

> 
>> So code just needs group cleanup on failed probing and fixing the mutex around pinctrl_generic_add_group().
>> 
>> I think we need the mutex because a race still can happen when create_pinctrl() is calling pcs_dt_node_to_map()
>> and pinctrl_generic_add_group() w/o being locked on pinctrl_maps_mutex.
>> 
>> The race I suspect is that two drivers are trying to insert the same name and may come
>> both to the conclusion that it does not yet exist. And both insert into the radix tree.
>> 
>> The window of risk is small though... It is in pinctrl_generic_add_group() between calling
>> pinctrl_generic_group_name_to_selector() and radix_tree_insert() so we probably won't
>> see it in real hardware tests.
> 
> Hmm but that race should be already fixed with mutex held
> by the pin controller drivers with these fixes? Or am I
> missing something still?

Hm. Maybe we refer to a different mutex?

I had seen the call sequence

create_pinctrl()-> pinctrl_dt_to_map() -> pcs_dt_node_to_map() -> pinctrl_generic_add_group()

w/o any lock inside.

There is a mutex_lock(&pinctrl_maps_mutex); in create_pinctrl(), but locked after that.

Or is there a lock outside of create_pinctrl()?

If I look into the stack dumps, call nesting is

driver_probe_device() -> pinctrl_bind_pins() -> devm_pinctrl_get() -> create_pinctrl()

They all do no locking.

Maybe I am missing something.

BR,
Nikolaus