From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [Patch net-next v5 3/3] igmp: convert RTNL lock to a spinlock
Date: Sat, 15 Jun 2013 01:26:08 -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 Sat, 2013-06-15 at 16:12 +0800, Cong Wang wrote:

> I _did_ try to replace spinlock with mutex, but apparently mutex_lock()
> can't be called with rcu_read_lock() held, which is the case in
> ip_mc_drop_socket().
> 

If you hold a mutex, there is no need for rcu_read_lock() at all.

Nobody can change the lists while you are the owner.

We already have nice helpers, lockdep enabled.

check rtnl_dereference() uses