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From:   Kalle Valo <kvalo@codeaurora.org>
To:     Johannes Berg <johannes@sipsolutions.net>
Cc:     Sumit Garg <sumit.garg@linaro.org>, linux-wireless@vger.kernel.org,
        davem@davemloft.net, kuba@kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, matthias.schoepfer@ithinx.io,
        Philipp.Berg@liebherr.com, Michael.Weitner@liebherr.com,
        daniel.thompson@linaro.org, loic.poulain@linaro.org,
        stable@vger.kernel.org
Subject: Re: [PATCH] mac80211: fix race in ieee80211_register_hw()
References: <1586175677-3061-1-git-send-email-sumit.garg@linaro.org>
        <87ftdgokao.fsf@tynnyri.adurom.net>
        <1e352e2130e19aec5aa5fc42db397ad50bb4ad05.camel@sipsolutions.net>
        <87r1x0zsgk.fsf@kamboji.qca.qualcomm.com>
        <a7e3e8cceff1301f5de5fb2c9aac62b372922b3e.camel@sipsolutions.net>
Date:   Mon, 06 Apr 2020 16:04:57 +0300
In-Reply-To: <a7e3e8cceff1301f5de5fb2c9aac62b372922b3e.camel@sipsolutions.net>
        (Johannes Berg's message of "Mon, 06 Apr 2020 14:53:49 +0200")
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Johannes Berg <johannes@sipsolutions.net> writes:

> On Mon, 2020-04-06 at 15:52 +0300, Kalle Valo wrote:
>> Johannes Berg <johannes@sipsolutions.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.
>
> Yeah, but that could be legitimate?

Ah, I misunderstood then. The way I have understood is that no rx frames
should be delivered (= calling ieee80211_rx()_ before start() is called,
but if that's not the case please ignore me :)

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