On Thu, Feb 23, 2017 at 12:20 AM, Jakub Kicinski <kubak...@wp.pl> wrote:
> On Wed, 22 Feb 2017 20:30:31 -0800, Jakub Kicinski wrote:
>> On Wed, 22 Feb 2017 14:27:45 -0800, Jakub Kicinski wrote:
>> > [ 1571.067134] ===============================
>> > [ 1571.071842] [ ERR: suspicious RCU usage. ]
>> > [ 1571.076546] 4.10.0-debug-03232-g12d656af4e3d #1 Tainted: G W O
>> > [ 1571.084166] -------------------------------
>> > [ 1571.088867] ../drivers/net/vxlan.c:2111 suspicious
>> > rcu_dereference_check() usage!
>> > [ 1571.097286]
>> > [ 1571.097286] other info that might help us debug this:
>> > [ 1571.097286]
>> > [ 1571.106305]
>> > [ 1571.106305] rcu_scheduler_active = 2, debug_locks = 1
>> > [ 1571.113654] 3 locks held by ping/13826:
>> > [ 1571.117968] #0: (sk_lock-AF_INET){+.+.+.}, at: [<ffffffffa1cd4972>]
>> > raw_sendmsg+0x14e2/0x2e40
>> > [ 1571.127758] #1: (rcu_read_lock_bh){......}, at: [<ffffffffa1be9594>]
>> > ip_finish_output2+0x274/0x1390
>> > [ 1571.138135] #2: (rcu_read_lock_bh){......}, at: [<ffffffffa1a9b63c>]
>> > __dev_queue_xmit+0x1ec/0x2750
>> ....
>>
>> diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
>> index 4e27c5b09600..8aa3e837cd6c 100644
>> --- a/drivers/net/vxlan.c
>> +++ b/drivers/net/vxlan.c
>> @@ -2109,7 +2109,7 @@ static void vxlan_xmit_one(struct sk_buff *skb, struct
>> net_device *dev,
>> vxlan->cfg.port_max, true);
>>
>> if (dst->sa.sa_family == AF_INET) {
>> - struct vxlan_sock *sock4 = rcu_dereference(vxlan->vn4_sock);
>> + struct vxlan_sock *sock4 =
>> rcu_dereference_bh(vxlan->vn4_sock);
>> struct rtable *rt;
>> __be16 df = 0;
>>
>> @@ -2148,7 +2148,7 @@ static void vxlan_xmit_one(struct sk_buff *skb, struct
>> net_device *dev,
>> src_port, dst_port, xnet, !udp_sum);
>> #if IS_ENABLED(CONFIG_IPV6)
>> } else {
>> - struct vxlan_sock *sock6 = rcu_dereference(vxlan->vn6_sock);
>> + struct vxlan_sock *sock6 =
>> rcu_dereference_bh(vxlan->vn6_sock);
>>
>> ndst = vxlan6_get_route(vxlan, dev, sock6, skb,
>> rdst ? rdst->remote_ifindex : 0, tos,
>>
>
> Ugh. Looks like this may not work even if it makes the splat go away.
> synchronize_net() doesn't seem to wait for the _bh() flavor of RCU, so
> we need to add syncronize_rcu_bh() call before freeing the socket or do
> a normal rcu_read_lock()/unlock() on the fast path. Any RCU experts
> want to comment? :)
>
I think both solutions would work. I prefer using rcu_read-lock in
fast path. We already execute vxlan rcv path in rcu read lock so it
would make it consistent with xmit path.
> FWIW geneve will need similar fix, I presume.
I agree.
