vrf: vrf_master_ifindex_rcu is not always called with rcu read lock

While running net-next I hit this:
[  634.073119] ===============================
[  634.073150] [ INFO: suspicious RCU usage. ]
[  634.073182] 4.2.0-rc6+ #45 Not tainted
[  634.073213] -------------------------------
[  634.073244] include/net/vrf.h:38 suspicious rcu_dereference_check()
usage!
[  634.073274]
               other info that might help us debug this:

[  634.073307]
               rcu_scheduler_active = 1, debug_locks = 1
[  634.073338] 2 locks held by swapper/0/0:
[  634.073369]  #0:  (((&n->timer))){+.-...}, at: [<ffffffff8112bc35>]
call_timer_fn+0x5/0x480
[  634.073412]  #1:  (slock-AF_INET){+.-...}, at: [<ffffffff8174f0f5>]
icmp_send+0x155/0x5f0
[  634.073450]
               stack backtrace:
[  634.073483] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.2.0-rc6+ #45
[  634.073514] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS
VirtualBox 12/01/2006
[  634.073545]  0000000000000000 0593ba8242d9ace4 ffff88002fc03b48
ffffffff81803f1b
[  634.073612]  0000000000000000 ffffffff81e12500 ffff88002fc03b78
ffffffff811003c5
[  634.073642]  0000000000000000 ffff88002ec4e600 ffffffff81f00f80
ffff88002fc03cf0
[  634.073669] Call Trace:
[  634.073694]  <IRQ>  [<ffffffff81803f1b>] dump_stack+0x4c/0x65
[  634.073728]  [<ffffffff811003c5>] lockdep_rcu_suspicious+0xc5/0x100
[  634.073763]  [<ffffffff8174eb56>] icmp_route_lookup+0x176/0x5c0
[  634.073793]  [<ffffffff8174f2fb>] ? icmp_send+0x35b/0x5f0
[  634.073818]  [<ffffffff8174f274>] ? icmp_send+0x2d4/0x5f0
[  634.073844]  [<ffffffff8174f3ce>] icmp_send+0x42e/0x5f0
[  634.073873]  [<ffffffff8170b662>] ipv4_link_failure+0x22/0xa0
[  634.073899]  [<ffffffff8174bdda>] arp_error_report+0x3a/0x80
[  634.073926]  [<ffffffff816d6100>] ? neigh_lookup+0x2c0/0x2c0
[  634.073952]  [<ffffffff816d396e>] neigh_invalidate+0x8e/0x110
[  634.073984]  [<ffffffff816d62ae>] neigh_timer_handler+0x1ae/0x290
[  634.074013]  [<ffffffff816d6100>] ? neigh_lookup+0x2c0/0x2c0
[  634.074013]  [<ffffffff8112bce3>] call_timer_fn+0xb3/0x480
[  634.074013]  [<ffffffff8112bc35>] ? call_timer_fn+0x5/0x480
[  634.074013]  [<ffffffff816d6100>] ? neigh_lookup+0x2c0/0x2c0
[  634.074013]  [<ffffffff8112c2bc>] run_timer_softirq+0x20c/0x430
[  634.074013]  [<ffffffff810af50e>] __do_softirq+0xde/0x630
[  634.074013]  [<ffffffff810afc97>] irq_exit+0x117/0x120
[  634.074013]  [<ffffffff81810976>] smp_apic_timer_interrupt+0x46/0x60
[  634.074013]  [<ffffffff8180e950>] apic_timer_interrupt+0x70/0x80
[  634.074013]  <EOI>  [<ffffffff8106b9d6>] ? native_safe_halt+0x6/0x10
[  634.074013]  [<ffffffff81101d8d>] ? trace_hardirqs_on+0xd/0x10
[  634.074013]  [<ffffffff81027d43>] default_idle+0x23/0x200
[  634.074013]  [<ffffffff8102852f>] arch_cpu_idle+0xf/0x20
[  634.074013]  [<ffffffff810f89ba>] default_idle_call+0x2a/0x40
[  634.074013]  [<ffffffff810f8dcc>] cpu_startup_entry+0x39c/0x4c0
[  634.074013]  [<ffffffff817f9cad>] rest_init+0x13d/0x150
[  634.074013]  [<ffffffff81f69038>] start_kernel+0x4a8/0x4c9
[  634.074013]  [<ffffffff81f68120>] ?
early_idt_handler_array+0x120/0x120
[  634.074013]  [<ffffffff81f68339>] x86_64_start_reservations+0x2a/0x2c
[  634.074013]  [<ffffffff81f68485>] x86_64_start_kernel+0x14a/0x16d

It would seem vrf_master_ifindex_rcu() can be called without RCU held in
other contexts as well so introduce a new helper which acquires rcu and
returns the ifindex.
Also add curly braces around both the "if" and "else" parts as per the
style guide.
Signed-off-by: NNikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/vrf.h

@@ -43,9 +43,9 @@ static inline int vrf_master_ifindex_rcu(const struct net_device *dev)
 	if (!dev)
 		return 0;
 
-	if (netif_is_vrf(dev))
+	if (netif_is_vrf(dev)) {
 		ifindex = dev->ifindex;
-	else {
+	} else {
 		vrf_ptr = rcu_dereference(dev->vrf_ptr);
 		if (vrf_ptr)
 			ifindex = vrf_ptr->ifindex;
@@ -54,6 +54,17 @@ static inline int vrf_master_ifindex_rcu(const struct net_device *dev)
 	return ifindex;
 }
 
+static inline int vrf_master_ifindex(const struct net_device *dev)
+{
+	int ifindex;
+
+	rcu_read_lock();
+	ifindex = vrf_master_ifindex_rcu(dev);
+	rcu_read_unlock();
+
+	return ifindex;
+}
+
 /* called with rcu_read_lock */
 static inline int vrf_dev_table_rcu(const struct net_device *dev)
 {
@@ -133,6 +144,11 @@ static inline int vrf_master_ifindex_rcu(const struct net_device *dev)
 	return 0;
 }
 
+static inline int vrf_master_ifindex(const struct net_device *dev)
+{
+	return 0;
+}
+
 static inline int vrf_dev_table_rcu(const struct net_device *dev)
 {
 	return 0;

net/ipv4/icmp.c

@@ -426,7 +426,7 @@ static void icmp_reply(struct icmp_bxm *icmp_param, struct sk_buff *skb)
 	fl4.flowi4_mark = mark;
 	fl4.flowi4_tos = RT_TOS(ip_hdr(skb)->tos);
 	fl4.flowi4_proto = IPPROTO_ICMP;
-	fl4.flowi4_oif = vrf_master_ifindex_rcu(skb->dev) ? : skb->dev->ifindex;
+	fl4.flowi4_oif = vrf_master_ifindex(skb->dev) ? : skb->dev->ifindex;
 	security_skb_classify_flow(skb, flowi4_to_flowi(&fl4));
 	rt = ip_route_output_key(net, &fl4);
 	if (IS_ERR(rt))
@@ -460,7 +460,7 @@ static struct rtable *icmp_route_lookup(struct net *net,
 	fl4->flowi4_proto = IPPROTO_ICMP;
 	fl4->fl4_icmp_type = type;
 	fl4->fl4_icmp_code = code;
-	fl4->flowi4_oif = vrf_master_ifindex_rcu(skb_in->dev) ? : skb_in->dev->ifindex;
+	fl4->flowi4_oif = vrf_master_ifindex(skb_in->dev) ? : skb_in->dev->ifindex;
 
 	security_skb_classify_flow(skb_in, flowi4_to_flowi(fl4));
 	rt = __ip_route_output_key(net, fl4);