[Letux-kernel] BUG: drivers/pinctrl/core: races in pinctrl_groups and deferred probing
H. Nikolaus Schaller
hns at goldelico.com
Mon Jun 18 20:30:17 CEST 2018
> Am 18.06.2018 um 20:17 schrieb Tony Lindgren <tony at atomide.com>:
> * H. Nikolaus Schaller <hns at goldelico.com> [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.
>> 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.
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