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From:   Krishna Chaitanya <chaitanya.mgit@gmail.com>
Date:   Mon, 6 Apr 2020 23:38:54 +0530
Message-ID: <CABPxzYJHjaLH+ozyFZx1hwXrNxdHgJaardk-kn7d72y7RC-=hw@mail.gmail.com>
Subject: Re: [PATCH] mac80211: fix race in ieee80211_register_hw()
To:     Johannes Berg <johannes@sipsolutions.net>
Cc:     Kalle Valo <kvalo@codeaurora.org>,
        Sumit Garg <sumit.garg@linaro.org>,
        linux-wireless <linux-wireless@vger.kernel.org>,
        "David S. Miller" <davem@davemloft.net>, kuba@kernel.org,
        netdev <netdev@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        =?UTF-8?Q?Matthias=2DPeter_Sch=C3=B6pfer?= 
        <matthias.schoepfer@ithinx.io>,
        "Berg Philipp (HAU-EDS)" <Philipp.Berg@liebherr.com>,
        "Weitner Michael (HAU-EDS)" <Michael.Weitner@liebherr.com>,
        Daniel Thompson <daniel.thompson@linaro.org>,
        Loic Poulain <loic.poulain@linaro.org>, stable@vger.kernel.org
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On Mon, Apr 6, 2020 at 8:36 PM Johannes Berg <johannes@sipsolutions.net> wrote:
>
> On Mon, 2020-04-06 at 19:55 +0530, Krishna Chaitanya wrote:
>
> > > iw phy0 interface add wlan0 type station
> > > ip link set wlan0 up
> > Ah okay, got it, thanks. Very narrow window though :-) as the
> > alloc_ordered_workqueue
> > doesn't need RTNL and there is a long way to go to do if_add() from
> > user and setup
> > the driver for interrupts.
>
> True, I do wonder how this is hit. Maybe something with no preempt and a
> uevent triggering things?
Probably, it might be specific to the dragonboard410c configuration

> > Again depends on the driver though, it
> > should properly handle
> > pending ieee80211_register_hw() with start().

> It could, but it'd be really tricky. Much better to fix mac80211.
Sure, anyways it is a good change.