netdev - Re: [BUG] deadlock in nl80211_vendor

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Date:   Fri, 25 Mar 2022 22:50:02 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     William McVicker <willmcvicker@...gle.com>,
        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>,
        Xinming Hu <huxinming820@...il.com>, kernel-team@...roid.com,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Cong Wang <cwang@...pensource.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [BUG] deadlock in nl80211_vendor_cmd

On Fri, 2022-03-25 at 14:48 -0700, Jakub Kicinski wrote:
> > 
> > > The WARN_ON() you suggested up front make perfect sense to me.
> > > You can also take the definition of net_unlink_todo() out of
> > > netdevice.h while at it because o_0  
> > 
> > Heh indeed, what?
> 
> To be clear - I just meant that it's declaring a static variable in 
> a header, so I doubt that it'll do the right thing unless it's only
> called from one compilation unit.

Right, it's odd. I just made a patch (will send in a minute) moving the
entire block to dev.c, which is the only user of any of it.

> > Ah, no. This isn't about locking in this case, it's literally about
> > ensuring that free_netdev() has been called in netdev_run_todo()?
> 
> Yup, multiple contexts sitting independently in netdev_run_todo() and
> chewing on netdevs is slightly different. destructors of those netdevs
> could be pointing at memory of a module being unloaded.

Right, thanks.

johannes