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 <[email protected]>
>>>>>
>>>>> Signed-off-by: Ding Tianhong <[email protected]>
>>>>> ---
>>>>> 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
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>> .
>>>>
>>>
>
>
> .
>
