Re: INFO: task hung in ip6gre_exit_batch_net

[Dmitry Vyukov]

On Tue, Jun 5, 2018 at 11:03 AM, Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> wrote:
> Hi, Dmirty!
>
> On 04.06.2018 18:22, Dmitry Vyukov wrote:
>> On Mon, Jun 4, 2018 at 5:03 PM, syzbot
>> <syzbot+bf78a74f82c1cf19069e@xxxxxxxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
>>
>> 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.