netdev - [PATCH net-next] ipv4: do not abuse GFP_ATOMIC in inet_netconf_notify

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Date:	Fri, 08 Jul 2016 05:18:24 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Masashi Honma <masashi.honma@...il.com>,
	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, Nicolas Dichtel <nicolas.dichtel@...nd.com>
Subject: [PATCH net-next] ipv4: do not abuse GFP_ATOMIC in
 inet_netconf_notify_devconf()

From: Eric Dumazet <edumazet@...gle.com>

inet_forward_change() runs with RTNL held.
We are allowed to sleep if required.

If we use __in_dev_get_rtnl() instead of __in_dev_get_rcu(),
we no longer have to use GFP_ATOMIC allocations in
inet_netconf_notify_devconf(), meaning we are less likely to miss
notifications under memory pressure, and wont touch precious memory
reserves either and risk dropping incoming packets.

inet_netconf_get_devconf() can also use GFP_KERNEL allocation.

Fixes: edc9e748934c ("rtnl/ipv4: use netconf msg to advertise forwarding status")
Fixes: 9e5511106f99 ("rtnl/ipv4: add support of RTM_GETNETCONF")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Nicolas Dichtel <nicolas.dichtel@...nd.com>
---
 net/ipv4/devinet.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index e333bc86bd39d8baf08ea336f20f99cc51ec945f..415e117967c775f805b43cd634bdf9a55f064e2f 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1834,7 +1834,7 @@ void inet_netconf_notify_devconf(struct net *net, int type, int ifindex,
 	struct sk_buff *skb;
 	int err = -ENOBUFS;
 
-	skb = nlmsg_new(inet_netconf_msgsize_devconf(type), GFP_ATOMIC);
+	skb = nlmsg_new(inet_netconf_msgsize_devconf(type), GFP_KERNEL);
 	if (!skb)
 		goto errout;
 
@@ -1846,7 +1846,7 @@ void inet_netconf_notify_devconf(struct net *net, int type, int ifindex,
 		kfree_skb(skb);
 		goto errout;
 	}
-	rtnl_notify(skb, net, 0, RTNLGRP_IPV4_NETCONF, NULL, GFP_ATOMIC);
+	rtnl_notify(skb, net, 0, RTNLGRP_IPV4_NETCONF, NULL, GFP_KERNEL);
 	return;
 errout:
 	if (err < 0)
@@ -1903,7 +1903,7 @@ static int inet_netconf_get_devconf(struct sk_buff *in_skb,
 	}
 
 	err = -ENOBUFS;
-	skb = nlmsg_new(inet_netconf_msgsize_devconf(NETCONFA_ALL), GFP_ATOMIC);
+	skb = nlmsg_new(inet_netconf_msgsize_devconf(NETCONFA_ALL), GFP_KERNEL);
 	if (!skb)
 		goto errout;
 
@@ -2027,16 +2027,16 @@ static void inet_forward_change(struct net *net)
 
 	for_each_netdev(net, dev) {
 		struct in_device *in_dev;
+
 		if (on)
 			dev_disable_lro(dev);
-		rcu_read_lock();
-		in_dev = __in_dev_get_rcu(dev);
+
+		in_dev = __in_dev_get_rtnl(dev);
 		if (in_dev) {
 			IN_DEV_CONF_SET(in_dev, FORWARDING, on);
 			inet_netconf_notify_devconf(net, NETCONFA_FORWARDING,
 						    dev->ifindex, &in_dev->cnf);
 		}
-		rcu_read_unlock();
 	}
 }