netdev - Re: net: deadlock on genl

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Message-ID: <CAM_iQpWjt=mt2+ukaO_TxGZFzTEo8CCAXHXdO2ag+vm_=qr0eQ@mail.gmail.com>
Date:   Sun, 5 Feb 2017 22:32:24 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzkaller <syzkaller@...glegroups.com>,
        Eric Dumazet <edumazet@...gle.com>,
        David Miller <davem@...emloft.net>,
        Matti Vaittinen <matti.vaittinen@...ia.com>,
        Tycho Andersen <tycho.andersen@...onical.com>,
        Florian Westphal <fw@...len.de>,
        stephen hemminger <stephen@...workplumber.org>,
        Tom Herbert <tom@...bertland.com>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Richard Guy Briggs <rgb@...hat.com>,
        netdev-owner@...r.kernel.org
Subject: Re: net: deadlock on genl_mutex

On Sun, Jan 29, 2017 at 2:11 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Fri, Dec 9, 2016 at 6:08 AM, Cong Wang <xiyou.wangcong@...il.com> wrote:
>>>> Chain exists of:
>>>>  Possible unsafe locking scenario:
>>>>
>>>>        CPU0                    CPU1
>>>>        ----                    ----
>>>>   lock(genl_mutex);
>>>>                                lock(nlk->cb_mutex);
>>>>                                lock(genl_mutex);
>>>>   lock(rtnl_mutex);
>>>>
>>>>  *** DEADLOCK ***
>>>
>>> This one looks legitimate, because nlk->cb_mutex could be rtnl_mutex.
>>> Let me think about it.
>>
>> Never mind. Actually both reports in this thread are legitimate.
>>
>> I know what happened now, the lock chain is so long, 4 locks are involved
>> to form a chain!!!
>>
>> Let me think about how to break the chain.
>
>
> Cong, any success with breaking the chain?

No luck yet. Each part of the chain seems legit, not sure which
one could be reordered. :-/