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From:   Lukas Bulwahn <lukas.bulwahn@gmail.com>
Date:   Fri, 29 Nov 2019 06:54:47 +0100
Message-ID: <CAKXUXMwwxvJYjB0BkcmYg=AkzxW37SPiEuhyFPoATzEVY-MC7g@mail.gmail.com>
Subject: Re: unregister_netdevice: waiting for DEV to become free (2)
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     syzbot <syzbot+30209ea299c09d8785c9@syzkaller.appspotmail.com>,
        YueHaibing <yuehaibing@huawei.com>,
        Jouni Hogander <jouni.hogander@unikie.com>,
        Julian Anastasov <ja@ssi.bg>, ddstreet@ieee.org,
        Dmitry Vyukov <dvyukov@google.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Netdev <netdev@vger.kernel.org>, syzkaller-bugs@googlegroups.com,
        Hulk Robot <hulkci@huawei.com>,
        "David S. Miller" <davem@davemloft.net>
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On Thu, Nov 28, 2019 at 10:56 AM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> Hello people involved in commit a3e23f719f5c4a38 ("net-sysfs: call dev_hold if kobject_init_and_add success")
> and commit b8eb718348b8fb30 ("net-sysfs: Fix reference count leak in rx|netdev_queue_add_kobject").
>
> syzbot is reporting that unregister_netdevice() hangs due to underflowing
> device refcount when kobject_init_and_add() failed due to -ENOMEM.
>

Tetsuo, would you happen to have a C reproducer program that creates
the trace you reported?

I could not quickly find one that by the date would fit to when we
included our change on this syzbot page:
https://syzkaller.appspot.com/bug?id=bae9a2236bfede42cf3d219e6bf6740c583568a4

Jouni, can you please follow up on this report.

Thanks.

Lukas