netdev - Re: rtnl_mutex deadlock?

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Date:	Tue, 4 Aug 2015 22:31:30 -0700
From:	Cong Wang <cwang@...pensource.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	David Miller <davem@...emloft.net>,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	Thomas Graf <tgraf@...g.ch>, Jiri Pirko <jiri@...nulli.us>,
	Scott Feldman <sfeldma@...il.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: rtnl_mutex deadlock?

On Tue, Aug 4, 2015 at 8:48 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> Sorry for the spamming of random rtnetlink people, but I just resumed
> my laptop at PDX, and networking was dead.
>
> It looks like a deadlock on rtnl_mutex, possibly due to some error
> path not releasing the lock. No network op was making any progress,
> and as you can see from the attached sysrq-w, it all seems to be hung
> in rtnl_lock().
>
> The call trace from NetworkManager looks different from the others,
> and looks to me like it might actually be a recursive invocation of
> rtnetlink_rcv(), but since I have a fairly light configuration on this
> laptop and don't have frame pointers enabled, I'm not sure how
> reliable that stack trace is. It might be just stale entries. But if
> they aren't stale, then that would certainly explain the deadlock.
>

You are right, looks like kernel received a GETLINK netlink message
from NetworkManager and then replied back but accidentally sent the
reply to itself, seems something wrong with NETLINK_CB(skb).portid.
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