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From:   Cong Wang <xiyou.wangcong@gmail.com>
Date:   Thu, 3 Sep 2020 11:11:06 -0700
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Subject: Re: INFO: task hung in tcf_ife_init
To:     Eric Dumazet <eric.dumazet@gmail.com>
Cc:     syzbot <syzbot+80e32b5d1f9923f8ace6@syzkaller.appspotmail.com>,
        David Miller <davem@davemloft.net>,
        Jamal Hadi Salim <jhs@mojatatu.com>,
        Jiri Pirko <jiri@resnulli.us>,
        Jakub Kicinski <kuba@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux Kernel Network Developers <netdev@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>
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On Thu, Sep 3, 2020 at 2:47 AM Eric Dumazet <eric.dumazet@gmail.com> wrote:
> This commit might be related :
>
> commit 4e407ff5cd67ec76eeeea1deec227b7982dc7f66
> Author: Cong Wang <xiyou.wangcong@gmail.com>
> Date:   Sun Aug 19 12:22:12 2018 -0700
>
>     act_ife: move tcfa_lock down to where necessary

It does not look like my commit's fault. From my _quick_ understanding
of this problem, we somehow have a "deadlock" situation:

Thread A allocates an IDR with a specific index and calls populate_metalist()
to re-accquire the RTNL lock.

Thread B gets RTNL lock right after thread A releases it, then it waits for
thread A to finally commit the IDR change.

Thanks.