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Date: Fri, 25 Mar 2022 14:48:39 -0700 From: Jakub Kicinski <kuba@...nel.org> To: Johannes Berg <johannes@...solutions.net> 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, 25 Mar 2022 22:25:05 +0100 Johannes Berg wrote: > > > With some suitable commentary, that might also be a reasonable thing? > > > __rtnl_unlock() is actually rather pretty rare, and not exported. > > > > The main use for it seems to be re-locking before loading a module, > > which TBH I have no idea why, is it just a cargo cult or a historical > > thing :S I don't see how letting netdevs leave before _loading_ > > a module makes any difference whatsoever. > > Indeed. > > > 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. > But (and now I'll CC even more people...) if we can actually have an > invariant that while RTNL is unlocked the todo list is empty, then we > also don't need rtnl_lock_unregistering_all(), and can remove the > netdev_unregistering_wq, etc., no? > > IOW, I'm not sure why we needed commit 50624c934db1 ("net: Delay > default_device_exit_batch until no devices are unregistering v2"), but I > also have little doubt that we did. > > 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. > Which we don't care about in cfg80211 - we just care about the list > being empty so there's no chance we'll reacquire the RTNL.
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