Messages in this thread | | | Date | Tue, 3 Jan 2017 16:57:46 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] rcu: fix the OOM problem of huge IP abnormal packet traffic |
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On Wed, Dec 28, 2016 at 04:13:15PM -0800, Paul E. McKenney wrote: > On Wed, Dec 28, 2016 at 01:58:06PM +0800, Ding Tianhong wrote: > > 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. > > From what I can see, there is absolutely no guarantee that > cond_resched_rcu_qs() will do local_bh_enable(), and thus no guarantee > that it will process any pending softirqs -- and that is not part of > its job in any case. So I cannot recommend the above patch. > > On efficient handling of large invalid packets (that is still the issue, > right?), I must defer to Dave and Eric.
On the perhaps unlikely off-chance that there is a fix for this outside of networking, what symptoms are you seeing without this fix in place? Still RCU CPU stall warnings? Soft lockups? Something else?
Thanx, Paul
> > 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 > > >>>>>> > > >>>>>> > > >>>>>> > > >>>>> > > >>>>> > > >>>>> . > > >>>>> > > >>>> > > >> > > >> > > >> . > > >> > >
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