ipv6: do not abuse GFP_ATOMIC in inet6_netconf_notify_devconf()

All inet6_netconf_notify_devconf() callers are in process context,
so we can use GFP_KERNEL allocations if we take care of not holding
a rwlock while not needed in ip6mr (we hold RTNL there)

Fixes: d67b8c616b48 ("netconf: advertise mc_forwarding status")
Fixes: f3a1bfb11ccb ("rtnl/ipv6: use netconf msg to advertise forwarding status")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index a1f6b7b..24f1b08 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -547,7 +547,7 @@
 	struct sk_buff *skb;
 	int err = -ENOBUFS;
 
-	skb = nlmsg_new(inet6_netconf_msgsize_devconf(type), GFP_ATOMIC);
+	skb = nlmsg_new(inet6_netconf_msgsize_devconf(type), GFP_KERNEL);
 	if (!skb)
 		goto errout;
 
@@ -559,7 +559,7 @@
 		kfree_skb(skb);
 		goto errout;
 	}
-	rtnl_notify(skb, net, 0, RTNLGRP_IPV6_NETCONF, NULL, GFP_ATOMIC);
+	rtnl_notify(skb, net, 0, RTNLGRP_IPV6_NETCONF, NULL, GFP_KERNEL);
 	return;
 errout:
 	rtnl_set_sk_err(net, RTNLGRP_IPV6_NETCONF, err);
diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index 487ef3b..c7ca0f5 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -1592,14 +1592,15 @@
 	if (likely(mrt->mroute6_sk == NULL)) {
 		mrt->mroute6_sk = sk;
 		net->ipv6.devconf_all->mc_forwarding++;
+	} else {
+		err = -EADDRINUSE;
+	}
+	write_unlock_bh(&mrt_lock);
+
+	if (!err)
 		inet6_netconf_notify_devconf(net, NETCONFA_MC_FORWARDING,
 					     NETCONFA_IFINDEX_ALL,
 					     net->ipv6.devconf_all);
-	}
-	else
-		err = -EADDRINUSE;
-	write_unlock_bh(&mrt_lock);
-
 	rtnl_unlock();
 
 	return err;
@@ -1617,11 +1618,11 @@
 			write_lock_bh(&mrt_lock);
 			mrt->mroute6_sk = NULL;
 			net->ipv6.devconf_all->mc_forwarding--;
+			write_unlock_bh(&mrt_lock);
 			inet6_netconf_notify_devconf(net,
 						     NETCONFA_MC_FORWARDING,
 						     NETCONFA_IFINDEX_ALL,
 						     net->ipv6.devconf_all);
-			write_unlock_bh(&mrt_lock);
 
 			mroute_clean_tables(mrt, false);
 			err = 0;