netdev - Re: [BUG] deadlock in nl80211_vendor

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Date:   Fri, 25 Mar 2022 21:21:11 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     William McVicker <willmcvicker@...gle.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, linux-wireless@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Amitkumar Karwar <amitkarwar@...il.com>,
        Ganapathi Bhat <ganapathi.bhat@....com>,
        Xinming Hu <huxinming820@...il.com>, kernel-team@...roid.com,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [BUG] deadlock in nl80211_vendor_cmd

On Fri, 2022-03-25 at 18:08 +0000, William McVicker wrote:
> 
> I'm able to reproduce this issue pretty easily with a Pixel 6 when I add
> support to allow vendor commands to request for the RTNL. 
> 

Hm, wait, which of the two issues?

> For this case, I just
> delay unlocking the RTNL until nl80211_vendor_cmds() at which point I check the
> flags to see if I should unlock before calling doit(). That allows me to run my
> tests again and hit this issue. I imagine that I could hit this issue without
> any changes if I re-work my vendor ops to not need the RTNL.

What are the vendor ops doing though?

If they're actually unregistering a netdev - which I believe you
mentioned earlier - then that's quite clearly going to cause an issue,
if you unlock RTNL while the wiphy mutex is still held.

If not, then I don't see right now how you'd be able to trigger any
issue here at all.

The original issue - that you rtnl_lock() yourself while the wiphy mutex
is held - can't happen anymore with your rework I guess.


johannes