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SubjectRe: [PATCH] mac80211: fix race in ieee80211_register_hw()
On Mon, 6 Apr 2020 at 18:38, Johannes Berg <johannes@sipsolutions.net> wrote:
>
> On Mon, 2020-04-06 at 16:04 +0300, Kalle Valo wrote:
> > 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 :)
>
> No no, that _is_ the case. But I think the "start wlan0" could end up
> calling it?
>

Sorry if I wasn't clear enough via the sequence diagram. It's a common
RX packet that arrives via ieee80211_tasklet_handler() which is
enabled via call to "struct ieee80211_ops::start" api.

-Sumit

> johannes
>

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