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

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Message-ID: <5718DA71.7050902@stressinduktion.org>
Date:	Thu, 21 Apr 2016 15:49:37 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>, Valdis.Kletnieks@...edu
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: linux-next: zillions of lockdep whinges in
 include/net/sock.h:1408

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.

Thanks Eric!