Re: [PATCH wireless-next v2 09/18] wifi: cfg80211: document wiphy mutex for radar/CAC events

[Johannes Berg <johannes@sipsolutions.net>]

Hi Brian,

Woah, thanks for looking through this! :-)

On Mon, 2026-10-05 at 10:46 -0700, Brian Norris wrote:
> > The DFS state of channels and the CAC state of the wdev is
> > protected by the wiphy mutex, so the radar and CAC events
> > must be reported by drivers with the wiphy mutex held. In
> > mac80211 we do this, but some drivers don't yet:
> >  - mwifiex/nxpwifi have an event handling worker,
> 
> FWIW, one of the two contexts that call cfg80211_cac_event() in mwifiex
> does *not* (by inspection) seem to hold this. 

Yeah I know - that's why I wrote "some drivers __don't__ yet".

It's always been broken though, and I kinda just wanted to move on. It's
racy, but I think mostly wrt. the valid_links warning (which isn't
relevant here) and the data accesses, nothing worse will happen.

> Is this something you'd
> prefer individual driver users/maintainers resolve?

I think so. Or we can discuss it should be async in cfg80211, or an
async version? I guess first we should discuss how to solve it either
way, and look at all the drivers that still have the issue.

> >  void cfg80211_cac_event(struct net_device *netdev,
> >  			const struct cfg80211_chan_def *chandef,
> 
> Should we add an assert to this API?
> 
> 	lockdep_assert_wiphy(wiphy);

Well I figured if I do that now then tools (and perhaps people) will
start complaining and that'd just put more pressure on everyone to fix
it ... that's why I didn't yet, but I guess I should've outlined that
better in the commit message (even after a --- marker).

johannes