ipv6,mcast: always hold idev->lock before mca_lock

dingtianhong reported the following deadlock detected by lockdep:

======================================================
[ INFO: possible circular locking dependency detected ]
3.4.24.05-0.1-default #1 Not tainted
-------------------------------------------------------
ksoftirqd/0/3 is trying to acquire lock:
(&ndev->lock){+.+...}, at: [<ffffffff8147f804>] ipv6_get_lladdr+0x74/0x120

but task is already holding lock:
(&mc->mca_lock){+.+...}, at: [<ffffffff8149d130>] mld_send_report+0x40/0x150

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&mc->mca_lock){+.+...}:
[<ffffffff810a8027>] validate_chain+0x637/0x730
[<ffffffff810a8417>] __lock_acquire+0x2f7/0x500
[<ffffffff810a8734>] lock_acquire+0x114/0x150
[<ffffffff814f691a>] rt_spin_lock+0x4a/0x60
[<ffffffff8149e4bb>] igmp6_group_added+0x3b/0x120
[<ffffffff8149e5d8>] ipv6_mc_up+0x38/0x60
[<ffffffff81480a4d>] ipv6_find_idev+0x3d/0x80
[<ffffffff81483175>] addrconf_notify+0x3d5/0x4b0
[<ffffffff814fae3f>] notifier_call_chain+0x3f/0x80
[<ffffffff81073471>] raw_notifier_call_chain+0x11/0x20
[<ffffffff813d8722>] call_netdevice_notifiers+0x32/0x60
[<ffffffff813d92d4>] __dev_notify_flags+0x34/0x80
[<ffffffff813d9360>] dev_change_flags+0x40/0x70
[<ffffffff813ea627>] do_setlink+0x237/0x8a0
[<ffffffff813ebb6c>] rtnl_newlink+0x3ec/0x600
[<ffffffff813eb4d0>] rtnetlink_rcv_msg+0x160/0x310
[<ffffffff814040b9>] netlink_rcv_skb+0x89/0xb0
[<ffffffff813eb357>] rtnetlink_rcv+0x27/0x40
[<ffffffff81403e20>] netlink_unicast+0x140/0x180
[<ffffffff81404a9e>] netlink_sendmsg+0x33e/0x380
[<ffffffff813c4252>] sock_sendmsg+0x112/0x130
[<ffffffff813c537e>] __sys_sendmsg+0x44e/0x460
[<ffffffff813c5544>] sys_sendmsg+0x44/0x70
[<ffffffff814feab9>] system_call_fastpath+0x16/0x1b

-> #0 (&ndev->lock){+.+...}:
[<ffffffff810a798e>] check_prev_add+0x3de/0x440
[<ffffffff810a8027>] validate_chain+0x637/0x730
[<ffffffff810a8417>] __lock_acquire+0x2f7/0x500
[<ffffffff810a8734>] lock_acquire+0x114/0x150
[<ffffffff814f6c82>] rt_read_lock+0x42/0x60
[<ffffffff8147f804>] ipv6_get_lladdr+0x74/0x120
[<ffffffff8149b036>] mld_newpack+0xb6/0x160
[<ffffffff8149b18b>] add_grhead+0xab/0xc0
[<ffffffff8149d03b>] add_grec+0x3ab/0x460
[<ffffffff8149d14a>] mld_send_report+0x5a/0x150
[<ffffffff8149f99e>] igmp6_timer_handler+0x4e/0xb0
[<ffffffff8105705a>] call_timer_fn+0xca/0x1d0
[<ffffffff81057b9f>] run_timer_softirq+0x1df/0x2e0
[<ffffffff8104e8c7>] handle_pending_softirqs+0xf7/0x1f0
[<ffffffff8104ea3b>] __do_softirq_common+0x7b/0xf0
[<ffffffff8104f07f>] __thread_do_softirq+0x1af/0x210
[<ffffffff8104f1c1>] run_ksoftirqd+0xe1/0x1f0
[<ffffffff8106c7de>] kthread+0xae/0xc0
[<ffffffff814fff74>] kernel_thread_helper+0x4/0x10

actually we can just hold idev->lock before taking pmc->mca_lock,
and avoid taking idev->lock again when iterating idev->addr_list,
since the upper callers of mld_newpack() already take
read_lock_bh(&idev->lock).

Reported-by: dingtianhong <[e-mail]>
Cc: dingtianhong <[e-mail]>
Cc: Hideaki YOSHIFUJI <[e-mail]>
Cc: David S. Miller <[e-mail]>
Cc: Hannes Frederic Sowa <[e-mail]>
Tested-by: Ding Tianhong <[e-mail]>
Tested-by: Chen Weilong <[e-mail]>
Signed-off-by: Cong Wang <[e-mail]>
Acked-by: Hannes Frederic Sowa <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/addrconf.h

···
 					       const struct in6_addr *daddr,
 					       unsigned int srcprefs,
 					       struct in6_addr *saddr);
+extern int			__ipv6_get_lladdr(struct inet6_dev *idev,
+						  struct in6_addr *addr,
+						  unsigned char banned_flags);
 extern int			ipv6_get_lladdr(struct net_device *dev,
 						struct in6_addr *addr,
 						unsigned char banned_flags);

net/ipv6/addrconf.c

···
 }
 EXPORT_SYMBOL(ipv6_dev_get_saddr);
 
-static int __ipv6_get_lladdr(struct inet6_dev *idev, struct in6_addr *addr,
-			     unsigned char banned_flags)
+int __ipv6_get_lladdr(struct inet6_dev *idev, struct in6_addr *addr,
+		      unsigned char banned_flags)
 {
 	struct inet6_ifaddr *ifp;
 	int err = -EADDRNOTAVAIL;

net/ipv6/mcast.c

···
 	hdr->daddr = *daddr;
 }
 
-static struct sk_buff *mld_newpack(struct net_device *dev, int size)
+static struct sk_buff *mld_newpack(struct inet6_dev *idev, int size)
 {
+	struct net_device *dev = idev->dev;
 	struct net *net = dev_net(dev);
 	struct sock *sk = net->ipv6.igmp_sk;
 	struct sk_buff *skb;
···
 
 	skb_reserve(skb, hlen);
 
-	if (ipv6_get_lladdr(dev, &addr_buf, IFA_F_TENTATIVE)) {
+	if (__ipv6_get_lladdr(idev, &addr_buf, IFA_F_TENTATIVE)) {
 		/* <draft-ietf-magma-mld-source-05.txt>:
 		 * use unspecified address as the source address
 		 * when a valid link-local address is not available.
···
 	struct mld2_grec *pgr;
 
 	if (!skb)
-		skb = mld_newpack(dev, dev->mtu);
+		skb = mld_newpack(pmc->idev, dev->mtu);
 	if (!skb)
 		return NULL;
 	pgr = (struct mld2_grec *)skb_put(skb, sizeof(struct mld2_grec));
···
 static struct sk_buff *add_grec(struct sk_buff *skb, struct ifmcaddr6 *pmc,
 	int type, int gdeleted, int sdeleted)
 {
-	struct net_device *dev = pmc->idev->dev;
+	struct inet6_dev *idev = pmc->idev;
+	struct net_device *dev = idev->dev;
 	struct mld2_report *pmr;
 	struct mld2_grec *pgr = NULL;
 	struct ip6_sf_list *psf, *psf_next, *psf_prev, **psf_list;
···
 		    AVAILABLE(skb) < grec_size(pmc, type, gdeleted, sdeleted)) {
 			if (skb)
 				mld_sendpack(skb);
-			skb = mld_newpack(dev, dev->mtu);
+			skb = mld_newpack(idev, dev->mtu);
 		}
 	}
 	first = 1;
···
 				pgr->grec_nsrcs = htons(scount);
 			if (skb)
 				mld_sendpack(skb);
-			skb = mld_newpack(dev, dev->mtu);
+			skb = mld_newpack(idev, dev->mtu);
 			first = 1;
 			scount = 0;
 		}
···
 	struct sk_buff *skb = NULL;
 	int type;
 
+	read_lock_bh(&idev->lock);
 	if (!pmc) {
-		read_lock_bh(&idev->lock);
 		for (pmc=idev->mc_list; pmc; pmc=pmc->next) {
 			if (pmc->mca_flags & MAF_NOREPORT)
 				continue;
···
 			skb = add_grec(skb, pmc, type, 0, 0);
 			spin_unlock_bh(&pmc->mca_lock);
 		}
-		read_unlock_bh(&idev->lock);
 	} else {
 		spin_lock_bh(&pmc->mca_lock);
 		if (pmc->mca_sfcount[MCAST_EXCLUDE])
···
 		skb = add_grec(skb, pmc, type, 0, 0);
 		spin_unlock_bh(&pmc->mca_lock);
 	}
+	read_unlock_bh(&idev->lock);
 	if (skb)
 		mld_sendpack(skb);
 }