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 <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
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>>
> > >>>>>
> > >>>>> .
> > >>>>>
> > >>>>
> > >>
> > >>
> > >> .
> > >>
> >
