Subject: Re: [PATCH] ipv6: Fix soft lockup for ipv6 network notifier.

From: Ding Tianhong <[email-masked]>
Date: Wed, 6 Jul 2016 16:15:10 +0800

On 2016/7/1 16:23, Eric Dumazet wrote:
> On Fri, 2016-07-01 at 16:10 +0800, Ding Tianhong wrote:
>> On 2016/7/1 15:57, Eric Dumazet wrote:
>>> On Fri, 2016-07-01 at 15:38 +0800, Ding Tianhong wrote:
>>> ...
>>>>  net/ipv6/addrconf.c | 6 ++++++
>>>>  1 file changed, 6 insertions(+)
>>>>
>>>> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
>>>> index f555f4f..e294a3d 100644
>>>> --- a/net/ipv6/addrconf.c
>>>> +++ b/net/ipv6/addrconf.c
>>>> @@ -3284,6 +3284,12 @@ restart:
>>>>  		spin_unlock_bh(&addrconf_hash_lock);
>>>>  	}
>>>>  
>>>> +	/*
>>>> +	 * It is safe here to schedule out to avoid softlocking if preempt
>>>> +	 * is disabled.
>>>> +	 */
>>>> +	cond_resched();
>>>> +
>>>>  	write_lock_bh(&idev->lock);
>>>>  
>>>>  	addrconf_del_rs_timer(idev);
>>>
>>> Seeing you apparently cooked your patch against an old kernel (which
>>> one ?) ...
>>>
>>> I tried vanilla net-next kernel, and apparently I could not trigger the
>>> softlockup you mentioned.
>>>
>>> Are you sure current kernel has a bug to begin with ?
>>>
>> have you disable the preempt? The problem will disappear if you enable the preempt voluntary or preempt.
>> CONFIG_PREEMPT_NONE=y
>> # CONFIG_PREEMPT_VOLUNTARY is not set
>> # CONFIG_PREEMPT is not set
>>
>> I test the 4.1 lts kernel and found this problem, and I didn't found any patch to fix this from linux 4.1, but I will try to test in 4.7 kernel version.
> 
> I usually do not have PREEMPT enabled in my kernels.
> 
> $ grep PREEMPT .config
> CONFIG_PREEMPT_NOTIFIERS=y
> CONFIG_PREEMPT_NONE=y
> # CONFIG_PREEMPT_VOLUNTARY is not set
> # CONFIG_PREEMPT is not set
> 
> Also the whole script is quite fast on latest kernels. I am guessing you
> are chasing an already fixed problem.
> 
> 
Hi Eric：

I had found out that the patch aaf92f(netfilter: conntrack: resched in nf_ct_iterate_cleanup) solve the problem, 
this patch add cond_sched() in the nf_ct_iterate_cleanup() which will be called in the net notifier chain every time,
and I revert this patch at kernel 4.7-rc4 , it will panic for soft lockup, so I am not sure whether our patch is need,
it looks like if I disable the CONFIG for netfilter that would register the nf_ct_iterate_cleanup as notifier, the problem still be exist.

Thanks.
Ding 

> .