Patchwork tcp_cubic: limit delayed_ack ratio to prevent divide error

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Submitter stephen hemminger
Date May 4, 2011, 8:04 p.m.
Message ID <20110504130456.425dee68@nehalam>
Download mbox | patch
Permalink /patch/94126/
State Accepted
Delegated to: David Miller
Headers show

Comments

stephen hemminger - May 4, 2011, 8:04 p.m.
TCP Cubic keeps a metric that estimates the amount of delayed
acknowledgements to use in adjusting the window. If an abnormally
large number of packets are acknowledged at once, then the update
could wrap and reach zero. This kind of ACK could only
happen when there was a large window and huge number of
ACK's were lost.

This patch limits the value of delayed ack ratio. The choice of 32
is just a conservative value since normally it should be range of 
1 to 4 packets.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>

---
Patch against 2.6.39-rc5+


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Jesse Brandeburg - May 4, 2011, 8:53 p.m.
On Wed, 4 May 2011, Stephen Hemminger wrote:

> TCP Cubic keeps a metric that estimates the amount of delayed
> acknowledgements to use in adjusting the window. If an abnormally
> large number of packets are acknowledged at once, then the update
> could wrap and reach zero. This kind of ACK could only
> happen when there was a large window and huge number of
> ACK's were lost.
> 
> This patch limits the value of delayed ack ratio. The choice of 32
> is just a conservative value since normally it should be range of 
> 1 to 4 packets.
> 
> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>

patch seems fine, but please credit the reporter (lkml@techboom.com) with 
reporting the issue with logs, maybe even with Reported-by: and some kind 
of reference to the panic message or the email thread in the text or 
header?

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TB - May 6, 2011, 4:15 p.m.
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 11-05-04 04:53 PM, Brandeburg, Jesse wrote:
> 
> 
> On Wed, 4 May 2011, Stephen Hemminger wrote:
> 
>> TCP Cubic keeps a metric that estimates the amount of delayed
>> acknowledgements to use in adjusting the window. If an abnormally
>> large number of packets are acknowledged at once, then the update
>> could wrap and reach zero. This kind of ACK could only
>> happen when there was a large window and huge number of
>> ACK's were lost.
>>
>> This patch limits the value of delayed ack ratio. The choice of 32
>> is just a conservative value since normally it should be range of 
>> 1 to 4 packets.
>>
>> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
> 
> patch seems fine, but please credit the reporter (lkml@techboom.com) with 
> reporting the issue with logs, maybe even with Reported-by: and some kind 
> of reference to the panic message or the email thread in the text or 
> header?

We're currently testing the patch on 6 production servers

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stephen hemminger - May 6, 2011, 4:53 p.m.
On Fri, 06 May 2011 12:15:46 -0400
TB <lkml@techboom.com> wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> On 11-05-04 04:53 PM, Brandeburg, Jesse wrote:
> > 
> > 
> > On Wed, 4 May 2011, Stephen Hemminger wrote:
> > 
> >> TCP Cubic keeps a metric that estimates the amount of delayed
> >> acknowledgements to use in adjusting the window. If an abnormally
> >> large number of packets are acknowledged at once, then the update
> >> could wrap and reach zero. This kind of ACK could only
> >> happen when there was a large window and huge number of
> >> ACK's were lost.
> >>
> >> This patch limits the value of delayed ack ratio. The choice of 32
> >> is just a conservative value since normally it should be range of 
> >> 1 to 4 packets.
> >>
> >> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
> > 
> > patch seems fine, but please credit the reporter (lkml@techboom.com) with 
> > reporting the issue with logs, maybe even with Reported-by: and some kind 
> > of reference to the panic message or the email thread in the text or 
> > header?
> 
> We're currently testing the patch on 6 production servers

Thank you, is there some regularity to the failures previously?
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TB - May 6, 2011, 5:39 p.m.
On 11-05-06 12:53 PM, Stephen Hemminger wrote:
> On Fri, 06 May 2011 12:15:46 -0400
> TB <lkml@techboom.com> wrote:
> 
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>> On 11-05-04 04:53 PM, Brandeburg, Jesse wrote:
>>>
>>>
>>> On Wed, 4 May 2011, Stephen Hemminger wrote:
>>>
>>>> TCP Cubic keeps a metric that estimates the amount of delayed
>>>> acknowledgements to use in adjusting the window. If an abnormally
>>>> large number of packets are acknowledged at once, then the update
>>>> could wrap and reach zero. This kind of ACK could only
>>>> happen when there was a large window and huge number of
>>>> ACK's were lost.
>>>>
>>>> This patch limits the value of delayed ack ratio. The choice of 32
>>>> is just a conservative value since normally it should be range of 
>>>> 1 to 4 packets.
>>>>
>>>> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
>>>
>>> patch seems fine, but please credit the reporter (lkml@techboom.com) with 
>>> reporting the issue with logs, maybe even with Reported-by: and some kind 
>>> of reference to the panic message or the email thread in the text or 
>>> header?
>>
>> We're currently testing the patch on 6 production servers
> 
> Thank you, is there some regularity to the failures previously?

Not really, there was more chance of it happening after a reboot and
during the night (when there is less traffic) for some weird reason.

As a workaround we switched most of the servers to reno
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David Miller - May 8, 2011, 10:52 p.m.
From: Stephen Hemminger <shemminger@vyatta.com>
Date: Wed, 4 May 2011 13:04:56 -0700

> TCP Cubic keeps a metric that estimates the amount of delayed
> acknowledgements to use in adjusting the window. If an abnormally
> large number of packets are acknowledged at once, then the update
> could wrap and reach zero. This kind of ACK could only
> happen when there was a large window and huge number of
> ACK's were lost.
> 
> This patch limits the value of delayed ack ratio. The choice of 32
> is just a conservative value since normally it should be range of 
> 1 to 4 packets.
> 
> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>

Applied, thanks Stephen.
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TB - May 11, 2011, 2:49 p.m.
On 11-05-06 12:53 PM, Stephen Hemminger wrote:
> On Fri, 06 May 2011 12:15:46 -0400
> TB <lkml@techboom.com> wrote:
> 
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>> On 11-05-04 04:53 PM, Brandeburg, Jesse wrote:
>>>
>>>
>>> On Wed, 4 May 2011, Stephen Hemminger wrote:
>>>
>>>> TCP Cubic keeps a metric that estimates the amount of delayed
>>>> acknowledgements to use in adjusting the window. If an abnormally
>>>> large number of packets are acknowledged at once, then the update
>>>> could wrap and reach zero. This kind of ACK could only
>>>> happen when there was a large window and huge number of
>>>> ACK's were lost.
>>>>
>>>> This patch limits the value of delayed ack ratio. The choice of 32
>>>> is just a conservative value since normally it should be range of 
>>>> 1 to 4 packets.
>>>>
>>>> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
>>>
>>> patch seems fine, but please credit the reporter (lkml@techboom.com) with 
>>> reporting the issue with logs, maybe even with Reported-by: and some kind 
>>> of reference to the panic message or the email thread in the text or 
>>> header?
>>
>> We're currently testing the patch on 6 production servers
> 
> Thank you, is there some regularity to the failures previously?

This is now being tested on about 50 servers and we just had another
panic, on a server with 2.6.38.5 and this patch.

[405542.454073] ------------[ cut here ]------------
[405542.454109] kernel BUG at net/ipv4/tcp_output.c:1006!
[405542.454136] invalid opcode: 0000 [#1]

[405542.454166] last sysfs file:
/sys/devices/pci0000:00/0000:00:1f.2/host6/scsi_host/host6/proc_name
[405542.454213] CPU 0

[405542.454220] Modules linked in:
 i2c_i801
 evdev
 i2c_core
 button
 [last unloaded: scsi_wait_scan]

[405542.454300]
[405542.454320] Pid: 0, comm: swapper Not tainted 2.6.38.5 #8

/

[405542.454379] RIP: 0010:[<ffffffff814e7ed2>]
 [<ffffffff814e7ed2>] tcp_fragment+0x22/0x29a
[405542.454433] RSP: 0018:ffff8800bf403a30  EFLAGS: 00010202
[405542.454460] RAX: ffff88000cd35000 RBX: ffff88006b84f480 RCX:
0000000000000218
[405542.454504] RDX: 0000000000001708 RSI: ffff88006b84f480 RDI:
ffff880008d6b200
[405542.454548] RBP: 0000000000001540 R08: 0000000000000002 R09:
000000001027984a
[405542.454592] R10: ffff8800b915f428 R11: ffff880008d6b200 R12:
ffff88006b84f4a8
[405542.454636] R13: 0000000000001708 R14: 0000000000000000 R15:
ffff880008d6b200
[405542.454680] FS:  0000000000000000(0000) GS:ffff8800bf400000(0000)
knlGS:0000000000000000
[405542.454726] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[405542.454754] CR2: 00007f94055c7000 CR3: 000000083e0bd000 CR4:
00000000000006f0
[405542.454798] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
0000000000000000
[405542.454842] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
0000000000000400
[405542.454886] Process swapper (pid: 0, threadinfo ffffffff8176c000,
task ffffffff81777020)
[405542.454931] Stack:
[405542.454951]  0000000000000000
 0000021808d6b798
 00000002000005b4
 ffff88006b84f480

[405542.455006]  ffff880008d6b200
 ffff88006b84f4a8
 0000000000000015
 0000000000000000

[405542.455061]  ffff880008d6b300
 ffffffff814df7a4
 ffff8802a3965140
 00000000000001a0

[405542.455115] Call Trace:
[405542.455137]  <IRQ>

[405542.455162]  [<ffffffff814df7a4>] ? tcp_mark_head_lost+0x13c/0x202
[405542.455192]  [<ffffffff814e33a8>] ? tcp_ack+0xe98/0x1a89
[405542.455220]  [<ffffffff814e42ca>] ? tcp_validate_incoming+0x69/0x290
[405542.455250]  [<ffffffff814e4c9b>] ? tcp_rcv_established+0x7aa/0xa13
[405542.455281]  [<ffffffff814ec60b>] ? tcp_v4_do_rcv+0x1b2/0x382
[405542.455310]  [<ffffffff814c95d4>] ? nf_iterate+0x40/0x78
[405542.455338]  [<ffffffff814ecc5f>] ? tcp_v4_rcv+0x484/0x797
[405542.455368]  [<ffffffff814d11c7>] ? ip_local_deliver_finish+0xab/0x139
[405542.455398]  [<ffffffff814ae2b3>] ? __netif_receive_skb+0x31c/0x349
[405542.455428]  [<ffffffff814aec82>] ? netif_receive_skb+0x67/0x6d
[405542.455457]  [<ffffffff814af1fb>] ? napi_gro_receive+0x9d/0xab
[405542.455485]  [<ffffffff814aed57>] ? napi_skb_finish+0x1c/0x31
[405542.455516]  [<ffffffff813e4248>] ? igb_poll+0x7d5/0xb2e
[405542.455544]  [<ffffffff813e432f>] ? igb_poll+0x8bc/0xb2e
[405542.455572]  [<ffffffff813e211a>] ? igb_msix_ring+0x6e/0x75
[405542.455602]  [<ffffffff8106749c>] ? handle_IRQ_event+0x51/0x119
[405542.455631]  [<ffffffff814af337>] ? net_rx_action+0xa7/0x212
[405542.455661]  [<ffffffff8103b6c2>] ? __do_softirq+0xbe/0x184
[405542.455690]  [<ffffffff8100364c>] ? call_softirq+0x1c/0x28
[405542.455719]  [<ffffffff81005085>] ? do_softirq+0x31/0x63
[405542.455746]  [<ffffffff8103b56c>] ? irq_exit+0x36/0x78
[405542.455773]  [<ffffffff81004784>] ? do_IRQ+0x98/0xae
[405542.455802]  [<ffffffff81562ed3>] ? ret_from_intr+0x0/0xe
[405542.455829]  <EOI>

[405542.455860]  [<ffffffff81009a41>] ? mwait_idle+0xb9/0xf3
[405542.455888]  [<ffffffff81001c6e>] ? cpu_idle+0x57/0x8d
[405542.455921]  [<ffffffff81801c49>] ? start_kernel+0x34e/0x35a
[405542.455950]  [<ffffffff81801398>] ? x86_64_start_kernel+0xf3/0xf9
[405542.455977] Code:
f>

[405542.456239] RIP
 [<ffffffff814e7ed2>] tcp_fragment+0x22/0x29a
[405542.456270]  RSP <ffff8800bf403a30>
[405542.456543] ---[ end trace 231aaa222f893065 ]---
[405542.456600] Kernel panic - not syncing: Fatal exception in interrupt
[405542.456659] Pid: 0, comm: swapper Tainted: G      D     2.6.38.5 #8
[405542.456719] Call Trace:
[405542.456770]  <IRQ>
 [<ffffffff81560960>] ? panic+0x9d/0x1a0
[405542.456863]  [<ffffffff81562ed3>] ? ret_from_intr+0x0/0xe
[405542.456923]  [<ffffffff810365bb>] ? kmsg_dump+0x46/0xec
[405542.456981]  [<ffffffff81006176>] ? oops_end+0x9f/0xac
[405542.457039]  [<ffffffff81003f83>] ? do_invalid_op+0x85/0x8f
[405542.457097]  [<ffffffff814e7ed2>] ? tcp_fragment+0x22/0x29a
[405542.457156]  [<ffffffff814e80a9>] ? tcp_fragment+0x1f9/0x29a
[405542.457216]  [<ffffffff810033d5>] ? invalid_op+0x15/0x20
[405542.457276]  [<ffffffff814e7ed2>] ? tcp_fragment+0x22/0x29a
[405542.457337]  [<ffffffff814df7a4>] ? tcp_mark_head_lost+0x13c/0x202
[405542.457400]  [<ffffffff814e33a8>] ? tcp_ack+0xe98/0x1a89
[405542.457461]  [<ffffffff814e42ca>] ? tcp_validate_incoming+0x69/0x290
[405542.457524]  [<ffffffff814e4c9b>] ? tcp_rcv_established+0x7aa/0xa13
[405542.457586]  [<ffffffff814ec60b>] ? tcp_v4_do_rcv+0x1b2/0x382
[405542.457645]  [<ffffffff814c95d4>] ? nf_iterate+0x40/0x78
[405542.457703]  [<ffffffff814ecc5f>] ? tcp_v4_rcv+0x484/0x797
[405542.457761]  [<ffffffff814d11c7>] ? ip_local_deliver_finish+0xab/0x139
[405542.457827]  [<ffffffff814ae2b3>] ? __netif_receive_skb+0x31c/0x349
[405542.457894]  [<ffffffff814aec82>] ? netif_receive_skb+0x67/0x6d
[405542.457953]  [<ffffffff814af1fb>] ? napi_gro_receive+0x9d/0xab
[405542.458021]  [<ffffffff814aed57>] ? napi_skb_finish+0x1c/0x31
[405542.458080]  [<ffffffff813e4248>] ? igb_poll+0x7d5/0xb2e
[405542.458138]  [<ffffffff813e432f>] ? igb_poll+0x8bc/0xb2e
[405542.458196]  [<ffffffff813e211a>] ? igb_msix_ring+0x6e/0x75
[405542.458254]  [<ffffffff8106749c>] ? handle_IRQ_event+0x51/0x119
[405542.458313]  [<ffffffff814af337>] ? net_rx_action+0xa7/0x212
[405542.458371]  [<ffffffff8103b6c2>] ? __do_softirq+0xbe/0x184
[405542.458430]  [<ffffffff8100364c>] ? call_softirq+0x1c/0x28
[405542.458488]  [<ffffffff81005085>] ? do_softirq+0x31/0x63
[405542.458545]  [<ffffffff8103b56c>] ? irq_exit+0x36/0x78
[405542.458602]  [<ffffffff81004784>] ? do_IRQ+0x98/0xae
[405542.458660]  [<ffffffff81562ed3>] ? ret_from_intr+0x0/0xe
[405542.458717]  <EOI>
 [<ffffffff81009a41>] ? mwait_idle+0xb9/0xf3
[405542.458810]  [<ffffffff81001c6e>] ? cpu_idle+0x57/0x8d
[405542.458867]  [<ffffffff81801c49>] ? start_kernel+0x34e/0x35a
[405542.458926]  [<ffffffff81801398>] ? x86_64_start_kernel+0xf3/0xf9


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stephen hemminger - May 11, 2011, 3:22 p.m.
On Wed, 11 May 2011 10:49:01 -0400
TB <lkml@techboom.com> wrote:

> On 11-05-06 12:53 PM, Stephen Hemminger wrote:
> > On Fri, 06 May 2011 12:15:46 -0400
> > TB <lkml@techboom.com> wrote:
> > 
> >> -----BEGIN PGP SIGNED MESSAGE-----
> >> Hash: SHA1
> >>
> >> On 11-05-04 04:53 PM, Brandeburg, Jesse wrote:
> >>>
> >>>
> >>> On Wed, 4 May 2011, Stephen Hemminger wrote:
> >>>
> >>>> TCP Cubic keeps a metric that estimates the amount of delayed
> >>>> acknowledgements to use in adjusting the window. If an abnormally
> >>>> large number of packets are acknowledged at once, then the update
> >>>> could wrap and reach zero. This kind of ACK could only
> >>>> happen when there was a large window and huge number of
> >>>> ACK's were lost.
> >>>>
> >>>> This patch limits the value of delayed ack ratio. The choice of 32
> >>>> is just a conservative value since normally it should be range of 
> >>>> 1 to 4 packets.
> >>>>
> >>>> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>

> >>>
> >>> patch seems fine, but please credit the reporter (lkml@techboom.com) with 
> >>> reporting the issue with logs, maybe even with Reported-by: and some kind 
> >>> of reference to the panic message or the email thread in the text or 
> >>> header?
> >>
> >> We're currently testing the patch on 6 production servers
> > 
> > Thank you, is there some regularity to the failures previously?
> 
> This is now being tested on about 50 servers and we just had another
> panic, on a server with 2.6.38.5 and this patch.
> 
> [405542.454073] ------------[ cut here ]------------
> [405542.454109] kernel BUG at net/ipv4/tcp_output.c:1006!
> [405542.454136] invalid opcode: 0000 [#1]
> 
> [405542.454166] last sysfs file:
> /sys/devices/pci0000:00/0000:00:1f.2/host6/scsi_host/host6/proc_name
> [405542.454213] CPU 0
> 
> [405542.454220] Modules linked in:
>  i2c_i801
>  evdev
>  i2c_core
>  button
>  [last unloaded: scsi_wait_scan]
> 
> [405542.454300]
> [405542.454320] Pid: 0, comm: swapper Not tainted 2.6.38.5 #8
> 
> /
> 
> [405542.454379] RIP: 0010:[<ffffffff814e7ed2>]
>  [<ffffffff814e7ed2>] tcp_fragment+0x22/0x29a
> [405542.454433] RSP: 0018:ffff8800bf403a30  EFLAGS: 00010202
> [405542.454460] RAX: ffff88000cd35000 RBX: ffff88006b84f480 RCX:
> 0000000000000218
> [405542.454504] RDX: 0000000000001708 RSI: ffff88006b84f480 RDI:
> ffff880008d6b200
> [405542.454548] RBP: 0000000000001540 R08: 0000000000000002 R09:
> 000000001027984a
> [405542.454592] R10: ffff8800b915f428 R11: ffff880008d6b200 R12:
> ffff88006b84f4a8
> [405542.454636] R13: 0000000000001708 R14: 0000000000000000 R15:
> ffff880008d6b200
> [405542.454680] FS:  0000000000000000(0000) GS:ffff8800bf400000(0000)
> knlGS:0000000000000000
> [405542.454726] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> [405542.454754] CR2: 00007f94055c7000 CR3: 000000083e0bd000 CR4:
> 00000000000006f0
> [405542.454798] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
> 0000000000000000
> [405542.454842] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
> 0000000000000400
> [405542.454886] Process swapper (pid: 0, threadinfo ffffffff8176c000,
> task ffffffff81777020)
> [405542.454931] Stack:
> [405542.454951]  0000000000000000
>  0000021808d6b798
>  00000002000005b4
>  ffff88006b84f480
> 
> [405542.455006]  ffff880008d6b200
>  ffff88006b84f4a8
>  0000000000000015
>  0000000000000000
> 
> [405542.455061]  ffff880008d6b300
>  ffffffff814df7a4
>  ffff8802a3965140
>  00000000000001a0
> 
> [405542.455115] Call Trace:
> [405542.455137]  <IRQ>
> 
> [405542.455162]  [<ffffffff814df7a4>] ? tcp_mark_head_lost+0x13c/0x202
> [405542.455192]  [<ffffffff814e33a8>] ? tcp_ack+0xe98/0x1a89
> [405542.455220]  [<ffffffff814e42ca>] ? tcp_validate_incoming+0x69/0x290
> [405542.455250]  [<ffffffff814e4c9b>] ? tcp_rcv_established+0x7aa/0xa13
> [405542.455281]  [<ffffffff814ec60b>] ? tcp_v4_do_rcv+0x1b2/0x382
> [405542.455310]  [<ffffffff814c95d4>] ? nf_iterate+0x40/0x78
> [405542.455338]  [<ffffffff814ecc5f>] ? tcp_v4_rcv+0x484/0x797
> [405542.455368]  [<ffffffff814d11c7>] ? ip_local_deliver_finish+0xab/0x139
> [405542.455398]  [<ffffffff814ae2b3>] ? __netif_receive_skb+0x31c/0x349
> [405542.455428]  [<ffffffff814aec82>] ? netif_receive_skb+0x67/0x6d
> [405542.455457]  [<ffffffff814af1fb>] ? napi_gro_receive+0x9d/0xab
> [405542.455485]  [<ffffffff814aed57>] ? napi_skb_finish+0x1c/0x31
> [405542.455516]  [<ffffffff813e4248>] ? igb_poll+0x7d5/0xb2e
> [405542.455544]  [<ffffffff813e432f>] ? igb_poll+0x8bc/0xb2e
> [405542.455572]  [<ffffffff813e211a>] ? igb_msix_ring+0x6e/0x75
> [405542.455602]  [<ffffffff8106749c>] ? handle_IRQ_event+0x51/0x119
> [405542.455631]  [<ffffffff814af337>] ? net_rx_action+0xa7/0x212
> [405542.455661]  [<ffffffff8103b6c2>] ? __do_softirq+0xbe/0x184
> [405542.455690]  [<ffffffff8100364c>] ? call_softirq+0x1c/0x28
> [405542.455719]  [<ffffffff81005085>] ? do_softirq+0x31/0x63
> [405542.455746]  [<ffffffff8103b56c>] ? irq_exit+0x36/0x78
> [405542.455773]  [<ffffffff81004784>] ? do_IRQ+0x98/0xae
> [405542.455802]  [<ffffffff81562ed3>] ? ret_from_intr+0x0/0xe
> [405542.455829]  <EOI>
> 
> [405542.455860]  [<ffffffff81009a41>] ? mwait_idle+0xb9/0xf3
> [405542.455888]  [<ffffffff81001c6e>] ? cpu_idle+0x57/0x8d
> [405542.455921]  [<ffffffff81801c49>] ? start_kernel+0x34e/0x35a
> [405542.455950]  [<ffffffff81801398>] ? x86_64_start_kernel+0xf3/0xf9

This panic is different than the last one.
It is coming from TCP fragment code being
called with an invalid skb. If I read the registers correctly,
skb->len (R14) = 0 and len (EDX) = 1708; the check here is failing.

int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
		 unsigned int mss_now)
{

	BUG_ON(len > skb->len);


Are you running with large (or small) MTU? What netfilter rules, perhaps
the firewall rule altered the packet.
TB - May 11, 2011, 3:35 p.m.
On 11-05-11 11:22 AM, Stephen Hemminger wrote:
> On Wed, 11 May 2011 10:49:01 -0400
> TB <lkml@techboom.com> wrote:
> 
>> On 11-05-06 12:53 PM, Stephen Hemminger wrote:
>>> On Fri, 06 May 2011 12:15:46 -0400
>>> TB <lkml@techboom.com> wrote:
>>>
>>>> -----BEGIN PGP SIGNED MESSAGE-----
>>>> Hash: SHA1
>>>>
>>>> On 11-05-04 04:53 PM, Brandeburg, Jesse wrote:
>>>>>
>>>>>
>>>>> On Wed, 4 May 2011, Stephen Hemminger wrote:
>>>>>
>>>>>> TCP Cubic keeps a metric that estimates the amount of delayed
>>>>>> acknowledgements to use in adjusting the window. If an abnormally
>>>>>> large number of packets are acknowledged at once, then the update
>>>>>> could wrap and reach zero. This kind of ACK could only
>>>>>> happen when there was a large window and huge number of
>>>>>> ACK's were lost.
>>>>>>
>>>>>> This patch limits the value of delayed ack ratio. The choice of 32
>>>>>> is just a conservative value since normally it should be range of 
>>>>>> 1 to 4 packets.
>>>>>>
>>>>>> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
> 
>>>>>
>>>>> patch seems fine, but please credit the reporter (lkml@techboom.com) with 
>>>>> reporting the issue with logs, maybe even with Reported-by: and some kind 
>>>>> of reference to the panic message or the email thread in the text or 
>>>>> header?
>>>>
>>>> We're currently testing the patch on 6 production servers
>>>
>>> Thank you, is there some regularity to the failures previously?
>>
>> This is now being tested on about 50 servers and we just had another
>> panic, on a server with 2.6.38.5 and this patch.
>>
>> [405542.454073] ------------[ cut here ]------------
>> [405542.454109] kernel BUG at net/ipv4/tcp_output.c:1006!
>> [405542.454136] invalid opcode: 0000 [#1]
>>
>> [405542.454166] last sysfs file:
>> /sys/devices/pci0000:00/0000:00:1f.2/host6/scsi_host/host6/proc_name
>> [405542.454213] CPU 0
>>
>> [405542.454220] Modules linked in:
>>  i2c_i801
>>  evdev
>>  i2c_core
>>  button
>>  [last unloaded: scsi_wait_scan]
>>
>> [405542.454300]
>> [405542.454320] Pid: 0, comm: swapper Not tainted 2.6.38.5 #8
>>
>> /
>>
>> [405542.454379] RIP: 0010:[<ffffffff814e7ed2>]
>>  [<ffffffff814e7ed2>] tcp_fragment+0x22/0x29a
>> [405542.454433] RSP: 0018:ffff8800bf403a30  EFLAGS: 00010202
>> [405542.454460] RAX: ffff88000cd35000 RBX: ffff88006b84f480 RCX:
>> 0000000000000218
>> [405542.454504] RDX: 0000000000001708 RSI: ffff88006b84f480 RDI:
>> ffff880008d6b200
>> [405542.454548] RBP: 0000000000001540 R08: 0000000000000002 R09:
>> 000000001027984a
>> [405542.454592] R10: ffff8800b915f428 R11: ffff880008d6b200 R12:
>> ffff88006b84f4a8
>> [405542.454636] R13: 0000000000001708 R14: 0000000000000000 R15:
>> ffff880008d6b200
>> [405542.454680] FS:  0000000000000000(0000) GS:ffff8800bf400000(0000)
>> knlGS:0000000000000000
>> [405542.454726] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>> [405542.454754] CR2: 00007f94055c7000 CR3: 000000083e0bd000 CR4:
>> 00000000000006f0
>> [405542.454798] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
>> 0000000000000000
>> [405542.454842] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
>> 0000000000000400
>> [405542.454886] Process swapper (pid: 0, threadinfo ffffffff8176c000,
>> task ffffffff81777020)
>> [405542.454931] Stack:
>> [405542.454951]  0000000000000000
>>  0000021808d6b798
>>  00000002000005b4
>>  ffff88006b84f480
>>
>> [405542.455006]  ffff880008d6b200
>>  ffff88006b84f4a8
>>  0000000000000015
>>  0000000000000000
>>
>> [405542.455061]  ffff880008d6b300
>>  ffffffff814df7a4
>>  ffff8802a3965140
>>  00000000000001a0
>>
>> [405542.455115] Call Trace:
>> [405542.455137]  <IRQ>
>>
>> [405542.455162]  [<ffffffff814df7a4>] ? tcp_mark_head_lost+0x13c/0x202
>> [405542.455192]  [<ffffffff814e33a8>] ? tcp_ack+0xe98/0x1a89
>> [405542.455220]  [<ffffffff814e42ca>] ? tcp_validate_incoming+0x69/0x290
>> [405542.455250]  [<ffffffff814e4c9b>] ? tcp_rcv_established+0x7aa/0xa13
>> [405542.455281]  [<ffffffff814ec60b>] ? tcp_v4_do_rcv+0x1b2/0x382
>> [405542.455310]  [<ffffffff814c95d4>] ? nf_iterate+0x40/0x78
>> [405542.455338]  [<ffffffff814ecc5f>] ? tcp_v4_rcv+0x484/0x797
>> [405542.455368]  [<ffffffff814d11c7>] ? ip_local_deliver_finish+0xab/0x139
>> [405542.455398]  [<ffffffff814ae2b3>] ? __netif_receive_skb+0x31c/0x349
>> [405542.455428]  [<ffffffff814aec82>] ? netif_receive_skb+0x67/0x6d
>> [405542.455457]  [<ffffffff814af1fb>] ? napi_gro_receive+0x9d/0xab
>> [405542.455485]  [<ffffffff814aed57>] ? napi_skb_finish+0x1c/0x31
>> [405542.455516]  [<ffffffff813e4248>] ? igb_poll+0x7d5/0xb2e
>> [405542.455544]  [<ffffffff813e432f>] ? igb_poll+0x8bc/0xb2e
>> [405542.455572]  [<ffffffff813e211a>] ? igb_msix_ring+0x6e/0x75
>> [405542.455602]  [<ffffffff8106749c>] ? handle_IRQ_event+0x51/0x119
>> [405542.455631]  [<ffffffff814af337>] ? net_rx_action+0xa7/0x212
>> [405542.455661]  [<ffffffff8103b6c2>] ? __do_softirq+0xbe/0x184
>> [405542.455690]  [<ffffffff8100364c>] ? call_softirq+0x1c/0x28
>> [405542.455719]  [<ffffffff81005085>] ? do_softirq+0x31/0x63
>> [405542.455746]  [<ffffffff8103b56c>] ? irq_exit+0x36/0x78
>> [405542.455773]  [<ffffffff81004784>] ? do_IRQ+0x98/0xae
>> [405542.455802]  [<ffffffff81562ed3>] ? ret_from_intr+0x0/0xe
>> [405542.455829]  <EOI>
>>
>> [405542.455860]  [<ffffffff81009a41>] ? mwait_idle+0xb9/0xf3
>> [405542.455888]  [<ffffffff81001c6e>] ? cpu_idle+0x57/0x8d
>> [405542.455921]  [<ffffffff81801c49>] ? start_kernel+0x34e/0x35a
>> [405542.455950]  [<ffffffff81801398>] ? x86_64_start_kernel+0xf3/0xf9
> 
> This panic is different than the last one.
> It is coming from TCP fragment code being
> called with an invalid skb. If I read the registers correctly,
> skb->len (R14) = 0 and len (EDX) = 1708; the check here is failing.
> 
> int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
> 		 unsigned int mss_now)
> {
> 
> 	BUG_ON(len > skb->len);
> 
> 
> Are you running with large (or small) MTU? What netfilter rules, perhaps
> the firewall rule altered the packet.


MTU 1500, No firewall rules (empty rules for filter, no mangle, no nat
modules)
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Patch

--- a/net/ipv4/tcp_cubic.c	2011-05-04 11:58:49.666027155 -0700
+++ b/net/ipv4/tcp_cubic.c	2011-05-04 12:52:34.716767304 -0700
@@ -93,6 +93,7 @@  struct bictcp {
 	u32	ack_cnt;	/* number of acks */
 	u32	tcp_cwnd;	/* estimated tcp cwnd */
 #define ACK_RATIO_SHIFT	4
+#define ACK_RATIO_LIMIT (32u << ACK_RATIO_SHIFT)
 	u16	delayed_ack;	/* estimate the ratio of Packets/ACKs << 4 */
 	u8	sample_cnt;	/* number of samples to decide curr_rtt */
 	u8	found;		/* the exit point is found? */
@@ -398,8 +399,12 @@  static void bictcp_acked(struct sock *sk
 	u32 delay;
 
 	if (icsk->icsk_ca_state == TCP_CA_Open) {
-		cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
-		ca->delayed_ack += cnt;
+		u32 ratio = ca->delayed_ack;
+
+		ratio -= ca->delayed_ack >> ACK_RATIO_SHIFT;
+		ratio += cnt;
+
+		ca->delayed_ack = min(ratio, ACK_RATIO_LIMIT);
 	}
 
 	/* Some calls are for duplicates without timetamps */