netdev - Re: INFO: task hung in ip6gre_exit_batch

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Date:   Tue, 5 Jun 2018 11:36:30 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     syzbot <syzbot+bf78a74f82c1cf19069e@...kaller.appspotmail.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        David Miller <davem@...emloft.net>,
        David Ahern <dsahern@...il.com>,
        Florian Westphal <fw@...len.de>, Jiri Benc <jbenc@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Xin Long <lucien.xin@...il.com>,
        mschiffer@...verse-factory.net, netdev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Vladislav Yasevich <vyasevich@...il.com>
Subject: Re: INFO: task hung in ip6gre_exit_batch_net

On Tue, Jun 5, 2018 at 11:03 AM, Kirill Tkhai <ktkhai@...tuozzo.com> wrote:
> Hi, Dmirty!
>
> On 04.06.2018 18:22, Dmitry Vyukov wrote:
>> On Mon, Jun 4, 2018 at 5:03 PM, syzbot
>> <syzbot+bf78a74f82c1cf19069e@...kaller.appspotmail.com> wrote:
>>> Hello,
>>>
>>> syzbot found the following crash on:
>>>
>>> HEAD commit:    bc2dbc5420e8 Merge branch 'akpm' (patches from Andrew)
>>> git tree:       upstream
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=164e42b7800000
>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=982e2df1b9e60b02
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=bf78a74f82c1cf19069e
>>> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>>>
>>> Unfortunately, I don't have any reproducer for this crash yet.
>>>
>>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>>> Reported-by: syzbot+bf78a74f82c1cf19069e@...kaller.appspotmail.com
>>
>> Another hang on rtnl lock:
>>
>> #syz dup: INFO: task hung in netdev_run_todo
>>
>> May be related to "unregister_netdevice: waiting for DEV to become free":
>> https://syzkaller.appspot.com/bug?id=1a97a5bd119fd97995f752819fd87840ab9479a9

netdev_wait_allrefs does not hold rtnl lock during waiting, so it must
be something different.


>> Any other explanations for massive hangs on rtnl lock for minutes?
>
> To exclude the situation, when a task exists with rtnl_mutex held:
>
> would the pr_warn() from print_held_locks_bug() be included in the console output
> if they appear?

Yes, everything containing "WARNING:" is detected as bug.