netdev - Re: linux-next: zillions of lockdep whinges in include/net/sock.h:1408

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Date:	Sun, 24 Apr 2016 14:38:33 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	hannes@...essinduktion.org
Cc:	eric.dumazet@...il.com, Valdis.Kletnieks@...edu,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: linux-next: zillions of lockdep whinges in
 include/net/sock.h:1408

From: Hannes Frederic Sowa <hannes@...essinduktion.org>
Date: Thu, 21 Apr 2016 15:49:37 +0200

> On 21.04.2016 15:31, Eric Dumazet wrote:
>> On Thu, 2016-04-21 at 05:05 -0400, Valdis.Kletnieks@...edu wrote:
>>> On Thu, 21 Apr 2016 09:42:12 +0200, Hannes Frederic Sowa said:
>>>> Hi,
>>>>
>>>> On Thu, Apr 21, 2016, at 02:30, Valdis Kletnieks wrote:
>>>>> linux-next 20160420 is whining at an incredible rate - in 20 minutes of
>>>>> uptime, I piled up some 41,000 hits from all over the place (cleaned up
>>>>> to skip the CPU and PID so the list isn't quite so long):
>>>>
>>>> Thanks for the report. Can you give me some more details:
>>>>
>>>> Is this an nfs socket? Do you by accident know if this socket went
>>>> through xs_reclassify_socket at any point? We do hold the appropriate
>>>> locks at that point but I fear that the lockdep reinitialization
>>>> confused lockdep.
>>>
>>> It wasn't an NFS socket, as NFS wasn't even active at the time.  I'm reasonably
>>> sure that multiple sockets were in play, given that tcp_v6_rcv and
>>> udpv6_queue_rcv_skb were both implicated.  I strongly suspect that pretty much
>>> any IPv6 traffic could do it - the frequency dropped off quite a bit when I
>>> closed firefox, which is usually a heavy network hitter on my laptop.
>> 
>> 
>> Looks like the following patch is needed, can you try it please ?
>> 
>> Thanks !
>> 
>> diff --git a/include/net/sock.h b/include/net/sock.h
>> index d997ec13a643..db8301c76d50 100644
>> --- a/include/net/sock.h
>> +++ b/include/net/sock.h
>> @@ -1350,7 +1350,8 @@ static inline bool lockdep_sock_is_held(const struct sock *csk)
>>  {
>>  	struct sock *sk = (struct sock *)csk;
>>  
>> -	return lockdep_is_held(&sk->sk_lock) ||
>> +	return !debug_locks ||
>> +	       lockdep_is_held(&sk->sk_lock) ||
>>  	       lockdep_is_held(&sk->sk_lock.slock);
>>  }
>>  #endif
> 
> I would prefer to add debug_locks at the WARN_ON level, like
> WARN_ON(debug_locks && !lockdep_sock_is_held(sk)), but I am not sure if
> this fixes the initial splat.

Can we finish this conversation out and come up with a final patch
for this soon?

Thanks.