netdev - Re: [PATCH v3 1/2] wifi: ath9k: fix races between ath9k_wmi_cmd and ath9k_wmi_ctrl

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Date: Thu, 18 May 2023 18:24:37 +0800
From: Hillf Danton <hdanton@...a.com>
To: Fedor Pchelkin <pchelkin@...ras.ru>
Cc: Toke Høiland-Jørgensen <toke@...e.dk>,
	Kalle Vallo <kvalo@...nel.org>,
	syzbot+f2cb6e0ffdb961921e4d@...kaller.appspotmail.com,
	linux-wireless@...r.kernel.org,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Alexey Khoroshilov <khoroshilov@...ras.ru>,
	lvc-project@...uxtesting.org
Subject: Re: [PATCH v3 1/2] wifi: ath9k: fix races between ath9k_wmi_cmd and ath9k_wmi_ctrl_rx

Fedor Pchelkin <pchelkin@...ras.ru> 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?

Given complete() not paired with wait_for_completion(), what is the
difference after this patch?