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 <dingtianh...@huawei.com>
>>>>>>
>>>>>> Signed-off-by: Ding Tianhong <dingtianh...@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
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> .
>>>>>
>>>>
>>
>>
>> .
>>
