netdev - Re: INFO: task hung in tcf_ife

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Message-ID: <CAM_iQpUBL+Wadb6f7iiKLXW0v8u3Hh+JERJAa7mEN94yZi0c1w@mail.gmail.com>
Date:   Thu, 3 Sep 2020 11:11:06 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     syzbot <syzbot+80e32b5d1f9923f8ace6@...kaller.appspotmail.com>,
        David Miller <davem@...emloft.net>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Jakub Kicinski <kuba@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: INFO: task hung in tcf_ife_init

On Thu, Sep 3, 2020 at 2:47 AM Eric Dumazet <eric.dumazet@...il.com> wrote:
> This commit might be related :
>
> commit 4e407ff5cd67ec76eeeea1deec227b7982dc7f66
> Author: Cong Wang <xiyou.wangcong@...il.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.