[PATCH net] openvswitch: fix a possible deadlock and lockdep warning

[Flavio Leitner <fbl-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

There are two problematic situations.

A deadlock can happen when is_percpu is false because it can get
interrupted while holding the spinlock. Then it executes
ovs_flow_stats_update() in softirq context which tries to get
the same lock.

The second sitation is that when is_percpu is true, the code
correctly disables BH only for the local CPU, but that confuses
lockdep enough to trigger the warning below.

This patch disables BH for both cases fixing the real deadlock
and the lockdep warning message.

=================================
[ INFO: inconsistent lock state ]
3.14.0-rc8-00007-g632b06a #1 Tainted: G          I
---------------------------------
inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
swapper/0/0 [HC0[0]:SC1[5]:HE1:SE0] takes:
(&(&cpu_stats->lock)->rlock){+.?...}, at: [<ffffffffa05dd8a1>] ovs_flow_stats_update+0x51/0xd0 [openvswitch]
{SOFTIRQ-ON-W} state was registered at:
[<ffffffff810f973f>] __lock_acquire+0x68f/0x1c40
[<ffffffff810fb4e2>] lock_acquire+0xa2/0x1d0
[<ffffffff817d8d9e>] _raw_spin_lock+0x3e/0x80
[<ffffffffa05dd9e4>] ovs_flow_stats_get+0xc4/0x1e0 [openvswitch]
[<ffffffffa05da855>] ovs_flow_cmd_fill_info+0x185/0x360 [openvswitch]
[<ffffffffa05daf05>] ovs_flow_cmd_build_info.constprop.27+0x55/0x90 [openvswitch]
[<ffffffffa05db41d>] ovs_flow_cmd_new_or_set+0x4dd/0x570 [openvswitch]
[<ffffffff816c245d>] genl_family_rcv_msg+0x1cd/0x3f0
[<ffffffff816c270e>] genl_rcv_msg+0x8e/0xd0
[<ffffffff816c0239>] netlink_rcv_skb+0xa9/0xc0
[<ffffffff816c0798>] genl_rcv+0x28/0x40
[<ffffffff816bf830>] netlink_unicast+0x100/0x1e0
[<ffffffff816bfc57>] netlink_sendmsg+0x347/0x770
[<ffffffff81668e9c>] sock_sendmsg+0x9c/0xe0
[<ffffffff816692d9>] ___sys_sendmsg+0x3a9/0x3c0
[<ffffffff8166a911>] __sys_sendmsg+0x51/0x90
[<ffffffff8166a962>] SyS_sendmsg+0x12/0x20
[<ffffffff817e3ce9>] system_call_fastpath+0x16/0x1b
irq event stamp: 1740726
hardirqs last  enabled at (1740726): [<ffffffff8175d5e0>] ip6_finish_output2+0x4f0/0x840
hardirqs last disabled at (1740725): [<ffffffff8175d59b>] ip6_finish_output2+0x4ab/0x840
softirqs last  enabled at (1740674): [<ffffffff8109be12>] _local_bh_enable+0x22/0x50
softirqs last disabled at (1740675): [<ffffffff8109db05>] irq_exit+0xc5/0xd0

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&(&cpu_stats->lock)->rlock);
  <Interrupt>
    lock(&(&cpu_stats->lock)->rlock);

 *** DEADLOCK ***

5 locks held by swapper/0/0:
 #0:  (((&ifa->dad_timer))){+.-...}, at: [<ffffffff810a7155>] call_timer_fn+0x5/0x320
 #1:  (rcu_read_lock){.+.+..}, at: [<ffffffff81788a55>] mld_sendpack+0x5/0x4a0
 #2:  (rcu_read_lock_bh){.+....}, at: [<ffffffff8175d149>] ip6_finish_output2+0x59/0x840
 #3:  (rcu_read_lock_bh){.+....}, at: [<ffffffff8168ba75>] __dev_queue_xmit+0x5/0x9b0
 #4:  (rcu_read_lock){.+.+..}, at: [<ffffffffa05e41b5>] internal_dev_xmit+0x5/0x110 [openvswitch]

stack backtrace:
CPU: 0 PID: 0 Comm: swapper/0 Tainted: G          I  3.14.0-rc8-00007-g632b06a #1
Hardware name:                  /DX58SO, BIOS SOX5810J.86A.5599.2012.0529.2218 05/29/2012
 0000000000000000 0fcf20709903df0c ffff88042d603808 ffffffff817cfe3c
 ffffffff81c134c0 ffff88042d603858 ffffffff817cb6da 0000000000000005
 ffffffff00000001 ffff880400000000 0000000000000006 ffffffff81c134c0
Call Trace:
 <IRQ>  [<ffffffff817cfe3c>] dump_stack+0x4d/0x66
 [<ffffffff817cb6da>] print_usage_bug+0x1f4/0x205
 [<ffffffff810f7f10>] ? check_usage_backwards+0x180/0x180
 [<ffffffff810f8963>] mark_lock+0x223/0x2b0
 [<ffffffff810f96d3>] __lock_acquire+0x623/0x1c40
 [<ffffffff810f5707>] ? __lock_is_held+0x57/0x80
 [<ffffffffa05e26c6>] ? masked_flow_lookup+0x236/0x250 [openvswitch]
 [<ffffffff810fb4e2>] lock_acquire+0xa2/0x1d0
 [<ffffffffa05dd8a1>] ? ovs_flow_stats_update+0x51/0xd0 [openvswitch]
 [<ffffffff817d8d9e>] _raw_spin_lock+0x3e/0x80
 [<ffffffffa05dd8a1>] ? ovs_flow_stats_update+0x51/0xd0 [openvswitch]
 [<ffffffffa05dd8a1>] ovs_flow_stats_update+0x51/0xd0 [openvswitch]
 [<ffffffffa05dcc64>] ovs_dp_process_received_packet+0x84/0x120 [openvswitch]
 [<ffffffff810f93f7>] ? __lock_acquire+0x347/0x1c40
 [<ffffffffa05e3bea>] ovs_vport_receive+0x2a/0x30 [openvswitch]
 [<ffffffffa05e4218>] internal_dev_xmit+0x68/0x110 [openvswitch]
 [<ffffffffa05e41b5>] ? internal_dev_xmit+0x5/0x110 [openvswitch]
 [<ffffffff8168b4a6>] dev_hard_start_xmit+0x2e6/0x8b0
 [<ffffffff8168be87>] __dev_queue_xmit+0x417/0x9b0
 [<ffffffff8168ba75>] ? __dev_queue_xmit+0x5/0x9b0
 [<ffffffff8175d5e0>] ? ip6_finish_output2+0x4f0/0x840
 [<ffffffff8168c430>] dev_queue_xmit+0x10/0x20
 [<ffffffff8175d641>] ip6_finish_output2+0x551/0x840
 [<ffffffff8176128a>] ? ip6_finish_output+0x9a/0x220
 [<ffffffff8176128a>] ip6_finish_output+0x9a/0x220
 [<ffffffff8176145f>] ip6_output+0x4f/0x1f0
 [<ffffffff81788c29>] mld_sendpack+0x1d9/0x4a0
 [<ffffffff817895b8>] mld_send_initial_cr.part.32+0x88/0xa0
 [<ffffffff817691b0>] ? addrconf_dad_completed+0x220/0x220
 [<ffffffff8178e301>] ipv6_mc_dad_complete+0x31/0x50
 [<ffffffff817690d7>] addrconf_dad_completed+0x147/0x220
 [<ffffffff817691b0>] ? addrconf_dad_completed+0x220/0x220
 [<ffffffff8176934f>] addrconf_dad_timer+0x19f/0x1c0
 [<ffffffff810a71e9>] call_timer_fn+0x99/0x320
 [<ffffffff810a7155>] ? call_timer_fn+0x5/0x320
 [<ffffffff817691b0>] ? addrconf_dad_completed+0x220/0x220
 [<ffffffff810a76c4>] run_timer_softirq+0x254/0x3b0
 [<ffffffff8109d47d>] __do_softirq+0x12d/0x480
 [<ffffffff8109db05>] irq_exit+0xc5/0xd0
 [<ffffffff817e5fd8>] do_IRQ+0x58/0xf0
 [<ffffffff817d9db2>] common_interrupt+0x72/0x72
 <EOI>  [<ffffffff8162b594>] ? cpuidle_enter_state+0x54/0xd0
 [<ffffffff8162b6c9>] cpuidle_idle_call+0xb9/0x380
 [<ffffffff8102633e>] arch_cpu_idle+0xe/0x40
 [<ffffffff8110d605>] cpu_startup_entry+0xf5/0x420
 [<ffffffff817bef3d>] rest_init+0x13d/0x150
 [<ffffffff817bee05>] ? rest_init+0x5/0x150
 [<ffffffff81f6b00c>] start_kernel+0x493/0x4b4
 [<ffffffff81f6a982>] ? repair_env_string+0x5c/0x5c
 [<ffffffff81f6a120>] ? early_idt_handlers+0x120/0x120
 [<ffffffff81f6a5ee>] x86_64_start_reservations+0x2a/0x2c
 [<ffffffff81f6a73d>] x86_64_start_kernel+0x14d/0x170

Signed-off-by: Flavio Leitner <fbl-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
 net/openvswitch/flow.c | 26 ++++++--------------------
 1 file changed, 6 insertions(+), 20 deletions(-)

diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
index dda451f..2998989 100644
--- a/net/openvswitch/flow.c
+++ b/net/openvswitch/flow.c
@@ -103,30 +103,24 @@ static void stats_read(struct flow_stats *stats,
 void ovs_flow_stats_get(struct sw_flow *flow, struct ovs_flow_stats *ovs_stats,
 			unsigned long *used, __be16 *tcp_flags)
 {
-	int cpu, cur_cpu;
+	int cpu;
 
 	*used = 0;
 	*tcp_flags = 0;
 	memset(ovs_stats, 0, sizeof(*ovs_stats));
 
+	local_bh_disable();
 	if (!flow->stats.is_percpu) {
 		stats_read(flow->stats.stat, ovs_stats, used, tcp_flags);
 	} else {
-		cur_cpu = get_cpu();
 		for_each_possible_cpu(cpu) {
 			struct flow_stats *stats;
 
-			if (cpu == cur_cpu)
-				local_bh_disable();
-
 			stats = per_cpu_ptr(flow->stats.cpu_stats, cpu);
 			stats_read(stats, ovs_stats, used, tcp_flags);
-
-			if (cpu == cur_cpu)
-				local_bh_enable();
 		}
-		put_cpu();
 	}
+	local_bh_enable();
 }
 
 static void stats_reset(struct flow_stats *stats)
@@ -141,25 +135,17 @@ static void stats_reset(struct flow_stats *stats)
 
 void ovs_flow_stats_clear(struct sw_flow *flow)
 {
-	int cpu, cur_cpu;
+	int cpu;
 
+	local_bh_disable();
 	if (!flow->stats.is_percpu) {
 		stats_reset(flow->stats.stat);
 	} else {
-		cur_cpu = get_cpu();
-
 		for_each_possible_cpu(cpu) {
-
-			if (cpu == cur_cpu)
-				local_bh_disable();
-
 			stats_reset(per_cpu_ptr(flow->stats.cpu_stats, cpu));
-
-			if (cpu == cur_cpu)
-				local_bh_enable();
 		}
-		put_cpu();
 	}
+	local_bh_enable();
 }
 
 static int check_header(struct sk_buff *skb, int len)
-- 
1.8.5.3