netdev - Re: [PATCH] tcp_cubic: fix divide error when SYN flood

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Date:	Mon, 21 Apr 2014 20:37:39 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Liu Yu <allanliuyu@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	Stephen Hemminger <shemminger@...tta.com>,
	netdev@...r.kernel.org
Subject: Re: [PATCH] tcp_cubic: fix divide error when SYN flood

On Tue, 2014-04-22 at 11:27 +0800, Liu Yu wrote:
> 

> 
> Hi Eric
> 
> below is the stack
> 
> <6>[27292.140097] possible SYN flooding on port 8080. Sending cookies.
> <6>[27352.212394] possible SYN flooding on port 8080. Sending cookies.
> <6>[27412.211454] possible SYN flooding on port 8080. Sending cookies.
> <6>[27472.212504] possible SYN flooding on port 8080. Sending cookies.
> <6>[27536.083145] possible SYN flooding on port 8080. Sending cookies.
> <6>[27596.092124] possible SYN flooding on port 8080. Sending cookies.
> <6>[27656.109832] possible SYN flooding on port 80. Sending cookies.
> <0>[27676.940730] divide error: 0000 [#1] SMP
> <0>[27676.987890] last sysfs file: /sys/class/scsi_host/host0/proc_name
> <4>[27677.060792] CPU 0
> 0
> <6>[27677.198382] RIP: 0010:[<ffffffff8176940d>]  [<ffffffff8176940d>] bictcp_cong_avoid+0x14d/0x2a0
> <6>[27677.301544] RSP: 0018:ffff8800282039e0  EFLAGS: 00010246
> <6>[27677.365088] RAX: 0000000000000e80 RBX: ffff88010eefd340 RCX: 0000000000000000
> <6>[27677.450468] RDX: 0000000000000000 RSI: ffff88010eefd6b8 RDI: 0000000000000367
> <6>[27677.535850] RBP: ffff8800282039f0 R08: 00000000000001d1 R09: 0000000000000004
> <6>[27677.621232] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000042e1612d
> <6>[27677.706612] R13: 0000000000000506 R14: 0000000042e1612d R15: 0000000000000004
> <6>[27677.791993] FS:  0000000000000000(0000) GS:ffff880028200000(0000) knlGS:0000000000000000
> <6>[27677.888815] CS:  0010 DS: 0018 ES: 0018 CR0: 000000008005003b
> <6>[27677.957556] CR2: 00007f9d7a94b000 CR3: 0000000001001000 CR4: 00000000000406f0
> <6>[27678.042938] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> <6>[27678.128317] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> <4>[27678.213700] Process swapper (pid: 0, threadinfo ffffffff81c3e000, task ffffffff81c413e0)
> <0>[27678.310520] Stack:
> <4>[27678.334544]  ffff88010eefd340 ffff88010eefd340 ffff880028203a10 ffffffff8173b286
> <4>[27678.421276] <0> 0000000042e1612d 0000000000000006 ffff880028203ad0 ffffffff81740970
> <4>[27678.513416] <0> ffff88010eefd3f0 0000000000000000 0000015128203b10 42e1612d42e160c5
> <0>[27678.607743] Call Trace:
> <0>[27678.636965]  <IRQ>
> <4>[27678.662136]  [<ffffffff8173b286>] tcp_cong_avoid+0x16/0x30
> <4>[27678.727754]  [<ffffffff81740970>] tcp_ack+0xd50/0x1270
> <4>[27678.789219]  [<ffffffff81741400>] ? tcp_validate_incoming+0x220/0x350
> <4>[27678.866280]  [<ffffffff81742863>] tcp_rcv_established+0x203/0x660
> <4>[27678.939181]  [<ffffffff81748daf>] tcp_v4_do_rcv+0x11f/0x290
> <4>[27679.005844]  [<ffffffff8170d51f>] ? nf_iterate+0x5f/0x90
> <4>[27679.069384]  [<ffffffff8174ae73>] tcp_v4_rcv+0x583/0x6e0
> <4>[27679.132925]  [<ffffffff8170d5be>] ? nf_hook_slow+0x6e/0xe0
> <4>[27679.198553]  [<ffffffff8172c080>] ? ip_local_deliver_finish+0x0/0x120
> <4>[27679.275610]  [<ffffffff8172c0df>] ip_local_deliver_finish+0x5f/0x120
> <4>[27679.351632]  [<ffffffff8172c66b>] ip_local_deliver+0x3b/0x90
> <4>[27679.419333]  [<ffffffff8172be52>] ip_rcv_finish+0x152/0x380
> <4>[27679.485995]  [<ffffffff8172c531>] ip_rcv+0x251/0x350
> <4>[27679.545376]  [<ffffffff816f17c7>] __netif_receive_skb+0x267/0x31

Sorry, could you provide kernel version as well ?

There is a bug somewhere else, as tcp_cong_avoid() should not have a
'negative' acked param.

Thanks


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