[PATCH v2] tipc: ensure head->lock is initialised

[Chris Packham <chris.packham@alliedtelesis.co.nz>]

tipc_named_node_up() creates a skb list. It passes the list to
tipc_node_xmit() which has some code paths that can call
skb_queue_purge() which relies on the list->lock being initialised.

The spin_lock is only needed if the messages end up on the receive path
but when the list is created in tipc_named_node_up() we don't
necessarily know if it is going to end up there.

Once all the skb list users are updated in tipc it will then be possible
to update them to use the unlocked variants of the skb list functions
and initialise the lock when we know the message will follow the receive
path.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
---

I'm updating our products to use the latest kernel. One change that we have that
doesn't appear to have been upstreamed is related to the following soft lockup.

NMI watchdog: BUG: soft lockup - CPU#3 stuck for 23s! [swapper/3:0]
Modules linked in: tipc jitterentropy_rng echainiv drbg platform_driver(O) ipifwd(PO)
CPU: 3 PID: 0 Comm: swapper/3 Tainted: P           O    4.4.6-at1 #1
task: a3054e00 ti: ac6b4000 task.ti: a307a000
NIP: 806891c4 LR: 804f5060 CTR: 804f50d0
REGS: ac6b59b0 TRAP: 0901   Tainted: P           O     (4.4.6-at1)
MSR: 00029002 <CE,EE,ME>  CR: 84002088  XER: 20000000

GPR00: 804f50fc ac6b5a60 a3054e00 00029002 00000101 01001011 00000000 00000001
GPR08: 00021002 c1502d1c ac6b5ae4 00000000 804f50d0
NIP [806891c4] _raw_spin_lock_irqsave+0x44/0x80
LR [804f5060] skb_dequeue+0x20/0x90
Call Trace:
[ac6b5a80] [804f50fc] skb_queue_purge+0x2c/0x50
[ac6b5a90] [c1511058] tipc_node_xmit+0x138/0x170 [tipc]
[ac6b5ad0] [c1509e58] tipc_named_node_up+0x88/0xa0 [tipc]
[ac6b5b00] [c150fc1c] tipc_netlink_compat_stop+0x9bc/0xf50 [tipc]
[ac6b5b20] [c1511638] tipc_rcv+0x418/0x9b0 [tipc]
[ac6b5bc0] [c150218c] tipc_bcast_stop+0xfc/0x7b0 [tipc]
[ac6b5bd0] [80504e38] __netif_receive_skb_core+0x468/0xa10
[ac6b5c70] [805082fc] netif_receive_skb_internal+0x3c/0xe0
[ac6b5ca0] [80642a48] br_handle_frame_finish+0x1d8/0x4d0
[ac6b5d10] [80642f30] br_handle_frame+0x1f0/0x330
[ac6b5d60] [80504ec8] __netif_receive_skb_core+0x4f8/0xa10
[ac6b5e00] [805082fc] netif_receive_skb_internal+0x3c/0xe0
[ac6b5e30] [8044c868] _dpa_rx+0x148/0x5c0
[ac6b5ea0] [8044b0c8] priv_rx_default_dqrr+0x98/0x170
[ac6b5ed0] [804d1338] qman_p_poll_dqrr+0x1b8/0x240
[ac6b5f00] [8044b1c0] dpaa_eth_poll+0x20/0x60
[ac6b5f20] [805087cc] net_rx_action+0x15c/0x320
[ac6b5f80] [8002594c] __do_softirq+0x13c/0x250
[ac6b5fe0] [80025c34] irq_exit+0xb4/0xf0
[ac6b5ff0] [8000d81c] call_do_irq+0x24/0x3c
[a307be60] [80004acc] do_IRQ+0x8c/0x120
[a307be80] [8000f450] ret_from_except+0x0/0x18
--- interrupt: 501 at arch_cpu_idle+0x24/0x70

Eyeballing the code I think it can still happen since tipc_named_node_up
allocates struct sk_buff_head head on the stack so it could have arbitrary
content.

Changes in v2:
- fixup commit subject
- add more information to commit message from mailing list discussion

 net/tipc/name_distr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/tipc/name_distr.c b/net/tipc/name_distr.c
index 61219f0b9677..44abc8e9c990 100644
--- a/net/tipc/name_distr.c
+++ b/net/tipc/name_distr.c
@@ -190,7 +190,7 @@ void tipc_named_node_up(struct net *net, u32 dnode)
 	struct name_table *nt = tipc_name_table(net);
 	struct sk_buff_head head;
 
-	__skb_queue_head_init(&head);
+	skb_queue_head_init(&head);
 
 	read_lock_bh(&nt->cluster_scope_lock);
 	named_distribute(net, &head, dnode, &nt->cluster_scope);
-- 
2.22.0