Subject: Re: [GIT]: Networking

From: Eric Dumazet <[email-masked]>
Date: Wed, 05 Aug 2009 09:19:32 +0200

Ingo Molnar a écrit :
> * Ingo Molnar <[email-masked]> wrote:
> 
>> FYI, -tip testing found that these bits trigger a missing lockdep 
>> annotation warning:
> 
> it's apparently using an zero-initialized spinlock. This is a 
> side-effect of:
> 
>         dev_unicast_init(dev);
> 
> in alloc_netdev_mq() making use of dev->addr_list_lock.
> 
> Wouldnt the patch below be the right fix? The device has just been 
> allocated freshly, it's not accessible anywhere yet so no locking is 
> needed at all - in fact it's wrong to lock it here (the lock isnt 
> initialized yet).
> 
> This bug was apparently introduced via:
> 
> | commit a6ac65db2329e7685299666f5f7b6093c7b0f3a0
> | Author: Jiri Pirko <[email-masked]>
> | Date:   Thu Jul 30 01:06:12 2009 +0000
> |
> |     net: restore the original spinlock to protect unicast list
> 
> it needlessly added new locking and apparently nobody ran this patch 
> with lockdep.
> 
> 	Ingo
> 
> Index: linux2/net/core/dev.c
> ===================================================================
> --- linux2.orig/net/core/dev.c
> +++ linux2/net/core/dev.c
> @@ -4007,9 +4007,7 @@ static void dev_unicast_flush(struct net
>  
>  static void dev_unicast_init(struct net_device *dev)
>  {
> -	netif_addr_lock_bh(dev);
>  	__hw_addr_init(&dev->uc);
> -	netif_addr_unlock_bh(dev);
>  }
>  
>  

Indeed, this function is static and thus only called from alloc_netdev_mq()