[PATCH net-next] ipv4: do not abuse GFP_ATOMIC in inet_netconf_notify_devconf()

[Eric Dumazet]

From: Eric Dumazet <eduma...@google.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 <eduma...@google.com>
Cc: Nicolas Dichtel <nicolas.dich...@6wind.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();
        }
 }