netdev - [PATCH 1/2] ipv6: rework the lock in addrconf_permanent

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Date:	Fri,  1 Apr 2016 16:45:44 +0800
From:	roy.qing.li@...il.com
To:	netdev@...r.kernel.org
Subject: [PATCH 1/2] ipv6: rework the lock in addrconf_permanent_addr

From: Li RongQing <roy.qing.li@...il.com>

1. nothing of idev is changed, so read lock is enough
2. ifp is changed, so used ifp->lock or cmpxchg to protect it

Signed-off-by: Li RongQing <roy.qing.li@...il.com>
---
 net/ipv6/addrconf.c | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 27aed1a..f6e7605b 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -3184,14 +3184,21 @@ static void addrconf_gre_config(struct net_device *dev)
 static void l3mdev_check_host_rt(struct inet6_dev *idev,
 				  struct inet6_ifaddr *ifp)
 {
+	struct rt6_info *rt = NULL;
+
+	spin_lock(&ifp->lock);
 	if (ifp->rt) {
 		u32 tb_id = l3mdev_fib_table(idev->dev) ? : RT6_TABLE_LOCAL;
 
 		if (tb_id != ifp->rt->rt6i_table->tb6_id) {
-			ip6_del_rt(ifp->rt);
+			rt = ifp->rt;
 			ifp->rt = NULL;
 		}
 	}
+	spin_unlock(&ifp->lock);
+
+	if (rt)
+		ip6_del_rt(rt);
 }
 #else
 static void l3mdev_check_host_rt(struct inet6_dev *idev,
@@ -3203,6 +3210,8 @@ static void l3mdev_check_host_rt(struct inet6_dev *idev,
 static int fixup_permanent_addr(struct inet6_dev *idev,
 				struct inet6_ifaddr *ifp)
 {
+	struct rt6_info *prev;
+
 	l3mdev_check_host_rt(idev, ifp);
 
 	if (!ifp->rt) {
@@ -3212,7 +3221,12 @@ static int fixup_permanent_addr(struct inet6_dev *idev,
 		if (unlikely(IS_ERR(rt)))
 			return PTR_ERR(rt);
 
-		ifp->rt = rt;
+		prev = cmpxchg(&ifp->rt, NULL, rt);
+
+		/*if cmpxchg failed*/
+		if (prev) {
+			ip6_rt_put(rt);
+		}
 	}
 
 	if (!(ifp->flags & IFA_F_NOPREFIXROUTE)) {
@@ -3234,21 +3248,21 @@ static void addrconf_permanent_addr(struct net_device *dev)
 	if (!idev)
 		return;
 
-	write_lock_bh(&idev->lock);
+	read_lock_bh(&idev->lock);
 
 	list_for_each_entry_safe(ifp, tmp, &idev->addr_list, if_list) {
 		if ((ifp->flags & IFA_F_PERMANENT) &&
 		    fixup_permanent_addr(idev, ifp) < 0) {
-			write_unlock_bh(&idev->lock);
+			read_unlock_bh(&idev->lock);
 			ipv6_del_addr(ifp);
-			write_lock_bh(&idev->lock);
+			read_lock_bh(&idev->lock);
 
 			net_info_ratelimited("%s: Failed to add prefix route for address %pI6c; dropping\n",
 					     idev->dev->name, &ifp->addr);
 		}
 	}
 
-	write_unlock_bh(&idev->lock);
+	read_unlock_bh(&idev->lock);
 }
 
 static int addrconf_notify(struct notifier_block *this, unsigned long event,
-- 
2.1.4