From mboxrd@z Thu Jan  1 00:00:00 1970
From: Yuchung Cheng <ycheng@google.com>
Subject: Re: IPv6 kernel warning
Date: Mon, 7 Oct 2013 12:51:27 -0700
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References: <20130920131153.GF12758@n2100.arm.linux.org.uk>
 <20130920160830.GA4241@marquez.int.rhx> <CAK6E8=eNFG0fic+NYeQBjEoUQMeZKSAT3LU0JSQyE-4i_cDaZQ@mail.gmail.com>
 <alpine.DEB.2.02.1310071111240.17658@dtop>
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Cc: Michele Baldessari <michele@acksyn.org>,
	Russell King - ARM Linux <linux@arm.linux.org.uk>,
	netdev <netdev@vger.kernel.org>,
	Neal Cardwell <ncardwell@google.com>,
	Nandita Dukkipati <nanditad@google.com>
To: dormando <dormando@rydia.net>
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On Mon, Oct 7, 2013 at 11:13 AM, dormando <dormando@rydia.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);
                }