linux-kernel - Re: net: deadlock on genl

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Message-ID: <CAM_iQpW2x5xeBpxnZx+k+vnKkjxWPycCBpiKZE41Kcp5gBsN4w@mail.gmail.com>
Date:   Thu, 8 Dec 2016 21:08:47 -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 Thu, Dec 8, 2016 at 4:32 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> On Thu, Dec 8, 2016 at 9:16 AM, Dmitry Vyukov <dvyukov@...gle.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.