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

[Paul E. McKenney]

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.

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@xxxxxxxxxx>
> >>
> >> Signed-off-by: Ding Tianhong <dingtianhong@xxxxxxxxxx>
> >> ---
> >>  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
> >>
> >>
> >>
> > 
> > 
> > .
> > 
>