netdev - Re: [PATCH net] net: neighbour: add neighbour dead check for neigh_timer

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Message-ID: <52B142AF.8070708@huawei.com>
Date:	Wed, 18 Dec 2013 14:37:35 +0800
From:	Ding Tianhong <dingtianhong@...wei.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	David Miller <davem@...emloft.net>, <yoshfuji@...ux-ipv6.org>,
	<joe@...ches.com>, <vfalico@...hat.com>, <netdev@...r.kernel.org>
Subject: Re: [PATCH net] net: neighbour: add neighbour dead check for neigh_timer_handler()

On 2013/12/5 11:17, Ding Tianhong wrote:
> On 2013/12/5 8:32, Gao feng wrote:
>> On 12/04/2013 11:24 PM, Eric Dumazet wrote:
>>> On Wed, 2013-12-04 at 17:16 +0800, Ding Tianhong wrote:
>>>>>> 						base->running_timer = neigh->timer;
>>>>>> 						neigh_timer_handler() => at this time, refcnt is 2;
>>>>>>
>>>>>> user->	neigh_changeaddr()
>>>>>> 	neigh_flush_dev();
>>>>>> 	neigh_del_imer, refcnt dec to 1;
>>>>>
>>>>> Nope : del_timer() would return 0 here, so we do not decrement refcnt.
>>>>>
>>>>
>>>> The first call for del_timer() will return 1, because the timer->entry.next is not NULL,
>>>> then in the neigh_destroy, the del_timer() again will return 0 because timer->entry.next is NULL. 
>>>
>>> Again no. You are very mistaken.
>>>
>>> del_timer() return code is not a hint. Its a precise meaning.
>>>
>>> It cannot return 1 if the timer function is running or is about to run.
>>>
>>> If you believe there is  bug in del_timer(), fix it ;)
>>>
>>>
>>
>> Yes, you are right, __run_timers did this job.
>> So We still don't know what's the root reason.
>>
> Yes, I miss it, the running timer is detached from the list, thanks for all above.
> 
> Regards
> Ding
> 


Hi Eric:

I was so doubt about the situation, can you give me some advise?

	CPU0					  CPU1					  CPU2
      --------		      			--------                		---------
neigh_timer_handler				
write_lock(n->lock);		
	...
write_unlock(n->lock);
n->ref_cnt = 2 or 3(if mode_time)				
	...					neigh_flush_dev
						write_lock(n->lock);
						n->ref_cnt = 2;
						n->nud_state = NUD_NONE;
						write_unlock(n->lock);
						neigh_release()
						n->ref_cnt = 1;
						...					neigh_periodic_work
											write_lock(n->lock);
											write_unlock(n->lock);
											neigh_release();
											kfree(n)
n->ops->solicit()									...
...

if that possible? or I was totally wrong? pls give me some advise if I miss something, thanks a lot.

Best Regards
Ding

>>
> 


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