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Date: Thu, 06 Jun 2013 08:36:03 +0800
From: Cong Wang <amwang@...hat.com>
To: netdev@...r.kernel.org
Cc: Eric Dumazet <eric.dumazet@...il.com>,
Stephen Hemminger <stephen@...workplumber.org>,
"David S. Miller" <davem@...emloft.net>
Subject: Re: [Patch net-next v2 3/3] igmp: convert RTNL lock to a spinlock
On Wed, 2013-06-05 at 17:38 +0800, Cong Wang wrote:
> - while ((i = rtnl_dereference(in_dev->mc_list)) != NULL) {
> - in_dev->mc_list = i->next_rcu;
> + spin_lock(&ipv4_sk_mc_lock);
> + while ((i = rcu_dereference_protected(in_dev->mc_list,
> + lockdep_is_held(&ipv4_sk_mc_lock))) != NULL) {
> + rcu_assign_pointer(in_dev->mc_list, i->next_rcu);
> in_dev->mc_count--;
>
> /* We've dropped the groups in ip_mc_down already */
> ip_mc_clear_src(i);
> ip_ma_put(i);
> }
> + spin_unlock(&ipv4_sk_mc_lock);
> + synchronize_rcu();
Hmm, it seems this kind synchronize_rcu() is not needed, since we don't
free anything here, not very sure if it is okay that readers still have
the old value of ->mc_list... I think probably yes.
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