Re: [PATCH] rcu: fix the OOM problem of huge IP abnormal packet traffic

[Ding Tianhong <dingtianhong@huawei.com>]

Hi, Paul:

I try to debug this problem and found this solution could work well for both problem scene.


diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 85c5a88..dbc14a7 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2172,7 +2172,7 @@ static int rcu_nocb_kthread(void *arg)
                        if (__rcu_reclaim(rdp->rsp->name, list))
                                cl++;
                        c++;
-                   local_bh_enable();
+                 _local_bh_enable();
                        cond_resched_rcu_qs();
                        list = next;
                }


The cond_resched_rcu_qs() would process the softirq if the softirq is pending, so no need to use
local_bh_enable() to process the softirq twice here, and it will avoid OOM when huge packets arrives,
what do you think about it? Please give me some suggestion.

Thanks.
Ding

On 2016/11/21 9:28, Ding Tianhong wrote:
> 
> 
> On 2016/11/21 8:13, Paul E. McKenney wrote:
>> On Sat, Nov 19, 2016 at 12:22:09AM -0800, Paul E. McKenney wrote:
>>> On Sat, Nov 19, 2016 at 03:50:32PM +0800, Ding Tianhong wrote:
>>>>
>>>>
>>>> On 2016/11/18 21:01, Paul E. McKenney wrote:
>>>>> On Fri, Nov 18, 2016 at 08:40:09PM +0800, Ding Tianhong wrote:
>>>>>> The commit bedc196915 ("rcu: Fix soft lockup for rcu_nocb_kthread")
>>>>>> will introduce a new problem that when huge IP abnormal packet arrived,
>>>>>> it may cause OOM and break the kernel, just like this:
>>>>>>
>>>>>> [   79.441538] mlx4_en: eth5: Leaving promiscuous mode steering mode:2
>>>>>> [  100.067032] ksoftirqd/0: page allocation failure: order:0, mode:0x120
>>>>>> [  100.067038] CPU: 0 PID: 3 Comm: ksoftirqd/0 Tainted: G           OE  ----V-------   3.10.0-327.28.3.28.x86_64 #1
>>>>>> [  100.067039] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.9.1-0-gb3ef39f-20161018_184732-HGH1000003483 04/01/2014
>>>>>> [  100.067041]  0000000000000120 00000000b080d798 ffff8802afd5b968 ffffffff81638cb9
>>>>>> [  100.067045]  ffff8802afd5b9f8 ffffffff81171380 0000000000000010 0000000000000000
>>>>>> [  100.067048]  ffff8802befd8000 00000000ffffffff 0000000000000001 00000000b080d798
>>>>>> [  100.067050] Call Trace:
>>>>>> [  100.067057]  [<ffffffff81638cb9>] dump_stack+0x19/0x1b
>>>>>> [  100.067062]  [<ffffffff81171380>] warn_alloc_failed+0x110/0x180
>>>>>> [  100.067066]  [<ffffffff81175b16>] __alloc_pages_nodemask+0x9b6/0xba0
>>>>>> [  100.067070]  [<ffffffff8151e400>] ? skb_add_rx_frag+0x90/0xb0
>>>>>> [  100.067075]  [<ffffffff811b6fba>] alloc_pages_current+0xaa/0x170
>>>>>> [  100.067080]  [<ffffffffa06b9be0>] mlx4_alloc_pages.isra.24+0x40/0x170 [mlx4_en]
>>>>>> [  100.067083]  [<ffffffffa06b9dec>] mlx4_en_alloc_frags+0xdc/0x220 [mlx4_en]
>>>>>> [  100.067086]  [<ffffffff8152eeb8>] ? __netif_receive_skb+0x18/0x60
>>>>>> [  100.067088]  [<ffffffff8152ef40>] ? netif_receive_skb+0x40/0xc0
>>>>>> [  100.067092]  [<ffffffffa06bb521>] mlx4_en_process_rx_cq+0x5f1/0xec0 [mlx4_en]
>>>>>> [  100.067095]  [<ffffffff8131027d>] ? list_del+0xd/0x30
>>>>>> [  100.067098]  [<ffffffff8152c90f>] ? __napi_complete+0x1f/0x30
>>>>>> [  100.067101]  [<ffffffffa06bbeef>] mlx4_en_poll_rx_cq+0x9f/0x170 [mlx4_en]
>>>>>> [  100.067103]  [<ffffffff8152f372>] net_rx_action+0x152/0x240
>>>>>> [  100.067107]  [<ffffffff81084d1f>] __do_softirq+0xef/0x280
>>>>>> [  100.067109]  [<ffffffff81084ee0>] run_ksoftirqd+0x30/0x50
>>>>>> [  100.067114]  [<ffffffff810ae93f>] smpboot_thread_fn+0xff/0x1a0
>>>>>> [  100.067117]  [<ffffffff8163e269>] ? schedule+0x29/0x70
>>>>>> [  100.067120]  [<ffffffff810ae840>] ? lg_double_unlock+0x90/0x90
>>>>>> [  100.067122]  [<ffffffff810a5d4f>] kthread+0xcf/0xe0
>>>>>> [  100.067124]  [<ffffffff810a5c80>] ? kthread_create_on_node+0x140/0x140
>>>>>> [  100.067127]  [<ffffffff81649198>] ret_from_fork+0x58/0x90
>>>>>> [  100.067129]  [<ffffffff810a5c80>] ? kthread_create_on_node+0x140/0x140
>>>>>>
>>>>>> ================================cut here=====================================
>>>>>>
>>>>>> The reason is that the huge abnormal IP packet will be received to net stack
>>>>>> and be dropped finally by dst_release, and the dst_release would use the rcuos
>>>>>> callback-offload kthread to free the packet, but the cond_resched_rcu_qs() will
>>>>>> calling do_softirq() to receive more and more IP abnormal packets which will be
>>>>>> throw into the RCU callbacks again later, the number of received packet is much
>>>>>> greater than the number of packets freed, it will exhaust the memory and then OOM,
>>>>>> so don't try to process any pending softirqs in the rcuos callback-offload kthread
>>>>>> is a more effective solution.
>>>>>
>>>>> OK, but we could still have softirqs processed by the grace-period kthread
>>>>> as a result of any number of other events.  So this change might reduce
>>>>> the probability of this problem, but it doesn't eliminate it.
>>>>>
>>>>> How huge are these huge IP packets?  Is the underlying problem that they
>>>>> are too large to use the memory-allocator fastpaths?
>>>>>
>>>>> 							Thanx, Paul
>>>>>
>>>>
>>>> I use the 40G mellanox NiC to receive packet, and the testgine could send Mac abnormal packet and
>>>> IP abnormal packet to full speed.
>>>>
>>>> The Mac abnormal packet would be dropped at low level and not be received to net stack,
>>>> but the IP abnormal packet will introduce this problem, every packet will looks as new dst first and
>>>> release later by dst_release because it is meaningless.
>>>>
>>>> dst_release->call_rcu(&dst->rcu_head, dst_destroy_rcu);
>>>>
>>>> so all packet will be freed until the rcuos callback-offload kthread processing, it will be a infinite loop
>>>> if huge packet is coming because the do_softirq will load more and more packet to the rcuos processing kthread,
>>>> so I still could not find a better way to fix this, btw, it is really hard to say the driver use too large memory-allocater
>>>> fastpaths, there is no memory leak and the Ixgbe may meet the same problem too.
>>
>> And following up on my fastpath point -- from what I can see, one
>> big effect of the large invalid packets is that they push processing
>> off of a number of fastpaths.  If these packets could be rejected with
>> less per-packet processing, I bet that things would work much better.
>>
>> 						Thanx, Paul
> 
> Yes, and I found the WARN_ON_ONCE(!irqs_disabled()) will be triggered if use _local_bh_enable here,
> so I think we could ask some help from Eric and David how to reject the huge number packets.
> 
> Thanks
> Ding
> 
>>
>>> The overall effect of these two patches is to move from enabling bh
>>> (and processing recent softirqs) to enabling bh without processing
>>> recent softirqs.  Is this really the correct way to solve this problem?
>>> What about this solution is avoiding re-introducing the original
>>> softlockups?  Have you talked to the networking guys about this issue?
>>>
>>> 							Thanx, Paul
>>>
>>>> Thanks.
>>>> Ding
>>>>
>>>>
>>>>>> Fix commit bedc196915 ("rcu: Fix soft lockup for rcu_nocb_kthread")
>>>>>> Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
>>>>>>
>>>>>> Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
>>>>>> ---
>>>>>>  kernel/rcu/tree_plugin.h | 3 +--
>>>>>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
>>>>>> index 85c5a88..760c3b5 100644
>>>>>> --- a/kernel/rcu/tree_plugin.h
>>>>>> +++ b/kernel/rcu/tree_plugin.h
>>>>>> @@ -2172,8 +2172,7 @@ static int rcu_nocb_kthread(void *arg)
>>>>>>  			if (__rcu_reclaim(rdp->rsp->name, list))
>>>>>>  				cl++;
>>>>>>  			c++;
>>>>>> -			local_bh_enable();
>>>>>> -			cond_resched_rcu_qs();
>>>>>> +			_local_bh_enable();
>>>>>>  			list = next;
>>>>>>  		}
>>>>>>  		trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
>>>>>> -- 
>>>>>> 1.9.0
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> .
>>>>>
>>>>
>>
>>
>> .
>>