[PATCH net-next] vrf: vrf_master_ifindex_rcu is not always called with rcu read lock

[Nikolay Aleksandrov <razor@blackwall.org>]

From: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>

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 to be sure acquire rcu before dereferencing the
vrf ptr.
Also add curly braces around both the "if" and "else" parts as per the
style guide.

Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
---
 include/net/vrf.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/net/vrf.h b/include/net/vrf.h
index 40e3793c7a05..22dfe2195092 100644
--- a/include/net/vrf.h
+++ b/include/net/vrf.h
@@ -35,7 +35,6 @@ struct net_vrf {
 
 
 #if IS_ENABLED(CONFIG_NET_VRF)
-/* called with rcu_read_lock() */
 static inline int vrf_master_ifindex_rcu(const struct net_device *dev)
 {
 	struct net_vrf_dev *vrf_ptr;
@@ -44,12 +43,14 @@ 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 {
+		rcu_read_lock();
 		vrf_ptr = rcu_dereference(dev->vrf_ptr);
 		if (vrf_ptr)
 			ifindex = vrf_ptr->ifindex;
+		rcu_read_unlock();
 	}
 
 	return ifindex;
-- 
2.4.3