Date:	Mon, 7 Oct 2013 13:00:56 -0700
From:	Yuchung Cheng <ycheng@...gle.com>
To:	dormando <dormando@...ia.net>
Cc:	Michele Baldessari <michele@...syn.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	netdev <netdev@...r.kernel.org>,
	Neal Cardwell <ncardwell@...gle.com>,
	Nandita Dukkipati <nanditad@...gle.com>
Subject: Re: IPv6 kernel warning

On Mon, Oct 7, 2013 at 12:56 PM, dormando <dormando@...ia.net> wrote:
> On Mon, 7 Oct 2013, Yuchung Cheng wrote:
>
>> On Mon, Oct 7, 2013 at 11:13 AM, dormando <dormando@...ia.net> wrote:
>> >
>> > > >
>> > > > there's been multiple reports about this one:
>> > > > https://bugzilla.redhat.com/show_bug.cgi?id=989251
>> > > > http://bugzilla.kernel.org/show_bug.cgi?id=60779
>> > > >
>> > > > Could you try Yuchung's debug patch?
>> > > > http://www.spinics.net/lists/netdev/msg250193.html
>> > > Yes it looks like the same bug. Please try that patch to help identify
>> > > this elusive bug.
>> > >
>> >
>> > Hi!
>> >
>> > We get this one a few times a day in production. Here's a warning with
>> > your debug trace in the line immediately following:
>> > (I censored a few things)
>> >
>> >  [125311.721950] ------------[ cut here ]------------
>> >  [125311.721961] WARNING: at net/ipv4/tcp_input.c:2776 tcp_fastretrans_alert+0xb58/0xc80()
>> >  [125311.721962] Modules linked in: bridge ip_vs macvlan coretemp crc32_pclmul ghash_clmulni_intel gpio_ich ipmi_watchdog microcode ipmi_devintf sb_edac lpc_ich edac_core mfd_core ipmi_si ipmi_msghandler iptable_nat nf_nat_ipv4 nf_nat ixgbe igb mdio i2c_algo_bit ptp pps_core
>> >  [125311.721981] CPU: 11 PID: 0 Comm: swapper/11 Not tainted 3.10.13 #1
>> >  [125311.721982] Hardware name: Supermicro XXXXXXXXXXX, BIOS 1.1 10/03/2012
>> >  [125311.721984]  ffffffff81a82007 ffff88407fc63958 ffffffff816bb9cc ffff88407fc63998
>> >  [125311.721986]  ffffffff8104b940 00ff8840ad904f82 ffff883b8a165b00 0000000000004120
>> >  [125311.721989]  0000000000000001 0000000000000019 0000000000000000 ffff88407fc639a8
>> >  [125311.721991] Call Trace:
>> >  [125311.721992]  <IRQ>  [<ffffffff816bb9cc>] dump_stack+0x19/0x1d
>> >  [125311.722002]  [<ffffffff8104b940>] warn_slowpath_common+0x70/0xa0
>> >  [125311.722005]  [<ffffffff8104b98a>] warn_slowpath_null+0x1a/0x20
>> >  [125311.722007]  [<ffffffff81616db8>] tcp_fastretrans_alert+0xb58/0xc80
>> >  [125311.722011]  [<ffffffff8161891f>] tcp_ack+0x6df/0xe90
>> >  [125311.722016]  [<ffffffff8164e0ca>] ? ipt_do_table+0x22a/0x680
>> >  [125311.722018]  [<ffffffff816194b3>] ? tcp_validate_incoming+0x63/0x320
>> >  [125311.722021]  [<ffffffff8161a55c>] tcp_rcv_established+0x2cc/0x810
>> >  [125311.722023]  [<ffffffff81622c84>] tcp_v4_do_rcv+0x254/0x4f0
>> >  [125311.722025]  [<ffffffff816245ac>] tcp_v4_rcv+0x5fc/0x750
>> >  [125311.722027]  [<ffffffff815ffa00>] ? ip_rcv+0x350/0x350
>> >  [125311.722032]  [<ffffffff815df3ad>] ? nf_hook_slow+0x7d/0x160
>> >  [125311.722034]  [<ffffffff815ffa00>] ? ip_rcv+0x350/0x350
>> >  [125311.722036]  [<ffffffff815fface>] ip_local_deliver_finish+0xce/0x250
>> >  [125311.722037]  [<ffffffff815ffc9c>] ip_local_deliver+0x4c/0x80
>> >  [125311.722039]  [<ffffffff815ff329>] ip_rcv_finish+0x119/0x360
>> >  [125311.722040]  [<ffffffff815ff8e0>] ip_rcv+0x230/0x350
>> >  [125311.722046]  [<ffffffff815b4067>] __netif_receive_skb_core+0x477/0x600
>> >  [125311.722049]  [<ffffffff815b4217>] __netif_receive_skb+0x27/0x70
>> >  [125311.722051]  [<ffffffff815b4354>] process_backlog+0xf4/0x1e0
>> >  [125311.722053]  [<ffffffff815b4b45>] net_rx_action+0xf5/0x250
>> >  [125311.722056]  [<ffffffff81053a5f>] __do_softirq+0xef/0x270
>> >  [125311.722058]  [<ffffffff81053cb5>] irq_exit+0x95/0xa0
>> >  [125311.722062]  [<ffffffff816c8f26>] do_IRQ+0x66/0xe0
>> >  [125311.722065]  [<ffffffff816bf62a>] common_interrupt+0x6a/0x6a
>> >  [125311.722065]  <EOI>  [<ffffffff8100abf1>] ? default_idle+0x21/0xc0
>> >  [125311.722082]  [<ffffffff8100a54f>] arch_cpu_idle+0xf/0x20
>> >  [125311.722086]  [<ffffffff8108f353>] cpu_startup_entry+0xb3/0x230
>> >  [125311.722091]  [<ffffffff816b439e>] start_secondary+0x1dc/0x1e3
>> >  [125311.722093] ---[ end trace e77cd5ba583fcbe9 ]---
>> >  [125311.722096] 355.355.1.355:22496 F0x4120 S1 s7 IF25+17-1-24f0 ur57 rr3 rt0 um0 hs23120 nxt23120
>> >
>> > It's been happening with all 3.10 kernels, and the one above is .13 as
>> > stated in the trace.
>>
>> Thanks! could you post the output of `sysctl -a |grep tcp`?
>>
>> I suspect tcp_process_tlp_ack() should not revert state to Open
>> directly, but calling tcp_try_keep_open() instead, similar to all the
>> undo processing in the tcp_fastretrans_alert(): after
>> tcp_end_cwnd_reduction(), the process (E) falls back to check other
>> stats before moving to CA_Open.
>>
>>
>> index 9c62257..9012b42 100644
>> --- a/net/ipv4/tcp_input.c
>> +++ b/net/ipv4/tcp_input.c
>> @@ -3314,7 +3314,7 @@ static void tcp_process_tlp_ack(struct sock *sk, u32 ack,
>>                         tcp_init_cwnd_reduction(sk, true);
>>                         tcp_set_ca_state(sk, TCP_CA_CWR);
>>                         tcp_end_cwnd_reduction(sk);
>> -                       tcp_set_ca_state(sk, TCP_CA_Open);
>> +                       tcp_try_keep_open(sk);
>>                         NET_INC_STATS_BH(sock_net(sk),
>>                                          LINUX_MIB_TCPLOSSPROBERECOVERY);
>>                 }
>>
>
> Should I apply this and see if the warning stops?
I'd like to hear what the authors of TLP think. In the mean time could
you help us collect more evidence by disabling TLP with
sysctl net.ipv4.tcp_early_retrans=2
and see if the problem still occurs? (it should not).

thanks

>
> net.ipv4.tcp_abort_on_overflow = 0
> net.ipv4.tcp_adv_win_scale = 1
> net.ipv4.tcp_allowed_congestion_control = cubic reno
> net.ipv4.tcp_app_win = 31
> net.ipv4.tcp_available_congestion_control = cubic reno westwood
> net.ipv4.tcp_base_mss = 512
> net.ipv4.tcp_challenge_ack_limit = 100
> net.ipv4.tcp_congestion_control = cubic
> net.ipv4.tcp_dma_copybreak = 262144
> net.ipv4.tcp_dsack = 1
> net.ipv4.tcp_early_retrans = 3


> net.ipv4.tcp_ecn = 2
> net.ipv4.tcp_fack = 1
> net.ipv4.tcp_fastopen = 0
> net.ipv4.tcp_fastopen_key = 009dc92c-82e3e514-d440ed23-c49b1a89
> net.ipv4.tcp_fin_timeout = 5
> net.ipv4.tcp_frto = 0
> net.ipv4.tcp_keepalive_intvl = 75
> net.ipv4.tcp_keepalive_probes = 9
> net.ipv4.tcp_keepalive_time = 1800
> net.ipv4.tcp_limit_output_bytes = 131072
> net.ipv4.tcp_low_latency = 0
> net.ipv4.tcp_max_orphans = 2000000
> net.ipv4.tcp_max_ssthresh = 0
> net.ipv4.tcp_max_syn_backlog = 65536
> net.ipv4.tcp_max_tw_buckets = 2000000
> net.ipv4.tcp_mem = 6188001      8250670 12376002
> net.ipv4.tcp_moderate_rcvbuf = 1
> net.ipv4.tcp_mtu_probing = 0
> net.ipv4.tcp_no_metrics_save = 1
> net.ipv4.tcp_orphan_retries = 0
> net.ipv4.tcp_reordering = 3
> net.ipv4.tcp_retrans_collapse = 1
> net.ipv4.tcp_retries1 = 3
> net.ipv4.tcp_retries2 = 15
> net.ipv4.tcp_rfc1337 = 0
> net.ipv4.tcp_rmem = 4096        87380   16777216
> net.ipv4.tcp_sack = 1
> net.ipv4.tcp_slow_start_after_idle = 0
> net.ipv4.tcp_stdurg = 0
> net.ipv4.tcp_syn_retries = 6
> net.ipv4.tcp_synack_retries = 5
> net.ipv4.tcp_syncookies = 1
> net.ipv4.tcp_thin_dupack = 0
> net.ipv4.tcp_thin_linear_timeouts = 0
> net.ipv4.tcp_timestamps = 1
> net.ipv4.tcp_tso_win_divisor = 3
> net.ipv4.tcp_tw_recycle = 0
> net.ipv4.tcp_tw_reuse = 0
> net.ipv4.tcp_user_cwnd_max = 20
> net.ipv4.tcp_window_scaling = 1
> net.ipv4.tcp_wmem = 4096        65536   16777216
> net.ipv4.tcp_workaround_signed_windows = 0
> net.ipv4.vs.secure_tcp = 0
>
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