netdev - Re: rtnl_mutex deadlock?

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Message-ID: <20150805074330.GA2084@nanopsycho.orion>
Date:	Wed, 5 Aug 2015 09:43:30 +0200
From:	Jiri Pirko <jiri@...nulli.us>
To:	Cong Wang <cwang@...pensource.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	Thomas Graf <tgraf@...g.ch>, Scott Feldman <sfeldma@...il.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: rtnl_mutex deadlock?

Wed, Aug 05, 2015 at 07:31:30AM CEST, cwang@...pensource.com wrote:
>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.

Indeed. Most probably, NETLINK_CB(skb).portid got zeroed.

Linus, are you able to reproduce this or is it a one-time issue?

Thanks!
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