From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [Patch net-next v3 3/3] igmp: convert RTNL lock to a spinlock
Date: Wed, 05 Jun 2013 19:40:00 -0700
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Cc: netdev@vger.kernel.org,
	Stephen Hemminger <stephen@networkplumber.org>,
	"David S. Miller" <davem@davemloft.net>
To: Cong Wang <amwang@redhat.com>
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On Thu, 2013-06-06 at 10:20 +0800, Cong Wang wrote:
> From: Cong Wang <amwang@redhat.com>
> 
> It is not necessary to hold RTNL lock to protect mc_list,
> at least IPv6 mcast is using a local spinlock, IPv4 can do
> this too. This patch converts RTNL lock+RCU to spinlock+RCU.
> 

Why are you doing this ? 

Really, holding a spinlock in this code instead of a mutex brings all
kind of problems.

For example, you have to use GFP_ATOMIC allocations instead of
GFP_KERNEL

Not counting the race/bug you added in ip_mc_join_group()