linux-kernel - Re: [PATCH] mac80211: fix race in ieee80211_register

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Message-ID: <87r1x0zsgk.fsf@kamboji.qca.qualcomm.com>
Date:   Mon, 06 Apr 2020 15:52:59 +0300
From:   Kalle Valo <kvalo@...eaurora.org>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     Sumit Garg <sumit.garg@...aro.org>, linux-wireless@...r.kernel.org,
        davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, matthias.schoepfer@...inx.io,
        Philipp.Berg@...bherr.com, Michael.Weitner@...bherr.com,
        daniel.thompson@...aro.org, loic.poulain@...aro.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] mac80211: fix race in ieee80211_register_hw()

Johannes Berg <johannes@...solutions.net> writes:

> On Mon, 2020-04-06 at 15:44 +0300, Kalle Valo wrote:
>> 
>> >     user-space  ieee80211_register_hw()  RX IRQ
>> >     +++++++++++++++++++++++++++++++++++++++++++++
>> >        |                    |             |
>> >        |<---wlan0---wiphy_register()      |
>> >        |----start wlan0---->|             |
>> >        |                    |<---IRQ---(RX packet)
>> >        |              Kernel crash        |
>> >        |              due to unallocated  |
>> >        |              workqueue.          |
>
> [snip]
>
>> I have understood that no frames should be received until mac80211 calls
>> struct ieee80211_ops::start:
>> 
>>  * @start: Called before the first netdevice attached to the hardware
>>  *         is enabled. This should turn on the hardware and must turn on
>>  *         frame reception (for possibly enabled monitor interfaces.)
>
> True, but I think he's saying that you can actually add and configure an
> interface as soon as the wiphy is registered?

With '<---IRQ---(RX packet)' I assumed wcn36xx is delivering a frame to
mac80211 using ieee80211_rx(), but of course I'm just guessing here.

-- 
https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches