Re: [PATCH v3 1/2] wifi: ath9k: fix races between ath9k_wmi_cmd and ath9k_wmi_ctrl_rx

[Toke Høiland-Jørgensen]

Fedor Pchelkin <pchelkin@xxxxxxxxx> writes:

> On Wed, Apr 26, 2023 at 07:07:08AM +0800, Hillf Danton wrote: 
>> Given similar wait timeout[1], just taking lock on the waiter side is not
>> enough wrt fixing the race, because in case job done on the waker side,
>> waiter needs to wait again after timeout.
>> 
>
> As I understand you correctly, you mean the case when a timeout occurs
> during ath9k_wmi_ctrl_rx() callback execution. I suppose if a timeout has
> occurred on a waiter's side, it should return immediately and doesn't have
> to care in which state the callback has been at that moment.
>
> AFAICS, this is controlled properly with taking a wmi_lock on waiter and
> waker sides, and there is no data corruption.
>
> If a callback has not managed to do its work entirely (performing a
> completion and subsequently waking waiting thread is included here), then,
> well, it is considered a timeout, in my opinion.
>
> Your suggestion makes a wmi_cmd call to give a little more chance for the
> belated callback to complete (although timeout has actually expired). That
> is probably good, but increasing a timeout value makes that job, too. I
> don't think it makes any sense on real hardware.
>
> Or do you mean there is data corruption that is properly fixed with your
> patch?
>
> That is, I agree there can be a situation when a callback makes all the
> logical work it should and it just hasn't got enough time to perform a
> completion before a timeout on waiter's side occurs. And this behaviour
> can be named "racy". But, technically, this seems to be a rather valid
> timeout.
>
>> [1] https://lore.kernel.org/lkml/9d9b9652-c1ac-58e9-2eab-9256c17b1da2@xxxxxxxxxxxxxxxxxxx/
>> 
>
> I don't think it's a similar case because wait_for_completion_state() is
> interruptible while wait_for_completion_timeout() is not.

Ping, Hillf?

-Toke