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Date:   Wed, 15 Nov 2023 08:34:59 +0100
From:   Johan Hovold <johan@kernel.org>
To:     Johannes Berg <johannes@sipsolutions.net>
Cc:     Emmanuel Grumbach <emmanuel.grumbach@intel.com>,
        linux-wireless@vger.kernel.org
Subject: Re: wifi: mac80211: lockdep splat with 6.7-rc1
Message-ID: <ZVR0o7Jvp6-zCS7R@hovoldconsulting.com>
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On Tue, Nov 14, 2023 at 06:02:33PM +0100, Johannes Berg wrote:
> On Tue, 2023-11-14 at 16:50 +0100, Johan Hovold wrote:

> > Naively adding locking around the call in ieee80211_get_tx_power()
> > (e.g. similar to 6b348f6e34ce ("wifi: mac80211: ethtool: always hold
> > wiphy mutex")) does not work as there are other paths that call this
> > function with the lock held, specifically via ieee80211_register_hw().
> 
> The latter we can just take the lock I guess?

ieee80211_register_hw() is specifically already taking the lock. 
 
> > [    7.127780]  ieee80211_get_tx_power+0x19c/0x1c0 [mac80211]
> > [    7.127859]  nl80211_send_iface+0x208/0x6a4 [cfg80211]
> > [    7.127946]  nl80211_dump_interface+0x120/0x254 [cfg80211]
> 
> And here maybe we should just take the mutex at the nl80211 level.

Yeah, it looks like you can possibly add it to nl80211_dump_interface().

nl80211_send_iface() is already called in paths like:

    ieee80211_get_tx_power+0x28/0x1c0 [mac80211]
    nl80211_send_iface+0x208/0x6a4 [cfg80211]
    nl80211_notify_iface+0x58/0xcc [cfg80211]
    cfg80211_register_wdev+0xa0/0x12c [cfg80211]
    cfg80211_register_netdevice+0x7c/0x108 [cfg80211]
    ieee80211_if_add+0x4b0/0x5cc [mac80211]
    ieee80211_register_hw+0xbec/0xc2c [mac80211]

> That's the nice thing now, it's shared between the layers :)
> 
> I can't do it right now, but I'll take a look tomorrow.

Sounds good, thanks.

Johan