On 07/06/2016 08:37 AM, Cong Wang wrote:
> On Tue, Jul 5, 2016 at 10:59 AM, Cong Wang <xiyou.wangcong@xxxxxxxxx> wrote:
>> On Mon, Jul 4, 2016 at 7:50 PM, Matt Bennett
>> <Matt.Bennett@xxxxxxxxxxxxxxxxxxx> wrote:
>>> Using printk I have confirmed that ppp_pernet() is called from
>>> ppp_connect_channel() when the BUG occurs (i.e. pch->chan_net is NULL).
>>>
>>> This behavior appears to have been introduced in commit 1f461dc ("ppp:
>>> take reference on channels netns").
>>
>> We have some race condition here, where a parallel ppp_unregister_channel()
>> could happen while we are in ppp_connect_channel().
>>
>> We need some synchronization for them. I am not sure what is the right lock
>> here since ppp locking looks crazy.
>
> Matt, could you try if the attached patch helps?
>
> Thanks!
>
I have given that patch a good amount of testing and the BUG_ON() no
longer is hit. Whether that is the best fix or not I am unsure?
Either way, the following comment in ppp_unregister_channel() seems
incorrect to me and should probably be deleted unless it is fixed?
/*
* This ensures that we have returned from any calls into the
* the channel's start_xmit or ioctl routine before we proceed.
*/
It appears mutex_lock(&ppp_mutex) what locks ppp_ioctl. ppp_xmit uses
ppp_xmit_lock(ppp) in ppp_xmit_process.
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