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

From: Ding Tianhong <[email-masked]>
Date: Fri, 1 Jul 2016 16:10:55 +0800

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.

Thanks
Ding

> Thanks.
> .