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Date: Mon, 22 Mar 2010 09:05:26 +0100 From: Eric Dumazet <eric.dumazet@...il.com> To: 杨硕 <shanqn@...il.com> Cc: netdev@...r.kernel.org Subject: Re: why does there need to lock? Le lundi 22 mars 2010 à 08:41 +0800, 杨硕 a écrit : > Hi, i'm confused about why does "rcu_assign_pointer(dev->ip_ptr, > in_dev);" need to rcu lock? > I am confused by your question rcu_assign_pointer doesnt need rcu lock. It only makes sure all previous memory changes are committed to memory before the "dev->ip_ptr = in_dev;" assignement, so that concurrent readers cannot find the new pointer and read previous values of dev->ip_ptr->fields > TIA :) > > static struct in_device *inetdev_init(struct net_device *dev) > { > struct in_device *in_dev; > > ASSERT_RTNL(); > > in_dev = kzalloc(sizeof(*in_dev), GFP_KERNEL); > if (!in_dev) > goto out; > memcpy(&in_dev->cnf, dev_net(dev)->ipv4.devconf_dflt, > sizeof(in_dev->cnf)); > in_dev->cnf.sysctl = NULL; > in_dev->dev = dev; > if ((in_dev->arp_parms = neigh_parms_alloc(dev, &arp_tbl)) == NULL) > goto out_kfree; > if (IPV4_DEVCONF(in_dev->cnf, FORWARDING)) > dev_disable_lro(dev); > /* Reference in_dev->dev */ > dev_hold(dev); > /* Account for reference dev->ip_ptr (below) */ > in_dev_hold(in_dev); > > devinet_sysctl_register(in_dev); > ip_mc_init_dev(in_dev); > if (dev->flags & IFF_UP) > ip_mc_up(in_dev); > > /* we can receive as soon as ip_ptr is set -- do this last */ > rcu_assign_pointer(dev->ip_ptr, in_dev); > out: > return in_dev; > out_kfree: > kfree(in_dev); > in_dev = NULL; > goto out; > } -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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