linux-kernel - Re: [syzbot] [wireless?] WARNING in ieee80211_link_release

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Date:   Mon, 04 Sep 2023 08:57:11 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     syzbot <syzbot+9817a610349542589c42@...kaller.appspotmail.com>,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, pabeni@...hat.com,
        syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [wireless?] WARNING in ieee80211_link_release_channel

On Sat, 2023-09-02 at 18:48 -0700, syzbot wrote:
> 
> WARNING: CPU: 0 PID: 7597 at net/mac80211/chan.c:2021 ieee80211_link_release_channel+0x19f/0x200 net/mac80211/chan.c:2021
> 

That's a lockdep warning, so it's kind of a known issue. I don't know if
I've yet encountered this specific way to get the locking checks
screaming, but generally we knew for a while that the locking was a bit
messy and possibly to some extent broken (*).

Anyway, point is - this is basically the reason I did this series:
https://lore.kernel.org/linux-wireless/20230828115927.116700-41-johannes@sipsolutions.net/

so this should go away - though sadly only in -next. Per the footnote, I
believe that the issue in the current kernel is mostly not an issue, and
it should only happen with multi-link in the first place. There may be
an issue in what syzbot found, processing a multi-link response or
something though.

johannes

(*) in many cases it's not _actually_ broken because we hold some common
outer lock anyway, so no data races are possible